# Kodowanie przy użyciu MEncodera

## Rippowanie DVD do wysokiej jakości pliku MPEG-4 ("DivX")

Jednym z często zadawanych pytań jest "Jak zrobić rip najlepszej jakości przy danej objętości?". Innym pytaniem jest "Jak zrobić najlepszy możliwy rip? Nie ważne jaka będzie objętość, chcę najlepszej jakości."

To drugie pytanie jest przynajmniej źle postawione. W końcu, jeśli nie przejmujesz się wielkością pliku, mógłbyć po prostu skopiować strumień MPEG-2 z DVD. Pewnie, dostaniesz AVI wielkości około 5GB, ale jeśli chcesz najlepszej jakości i nie przejmujesz się wielkością to jest to najlepsze wyjście.

Tak na prawdę, powodem dla którego chcesz przekodować DVD na MPEG-4 jest to, że przejmujesz się wielkością pliku.

Ciężko jest pokazać książkowy przepis na tworzenie ripu DVD bardzo wysokiej jakości. Trzeba wziąć pod uwagę kilka czynników, i powinieneś rozumieć szczegóły procesu, albo jest duża szansa że nie będziesz zadowolony z wyników. Poniżej zbadamy niektóre problemy i pokażemy przykład. Zakładamy że używasz libavcodec do kodowania obrazu, chociaż ta sama teoria działą też przy innych kodekach.

Jeśli to wydaje Ci się za dużo, to pewnie powinieneś użyć jednej z wielu nakładek dostępnych w sekcji MEncodera naszej strony z powiązanymi projektami. W ten sposób, powinno się udać otrzymać ripy wysokiej jakości bez zbyt myślenia za dużo, ponieważ te narzędzia są projektowane by podejmować za Ciebie mądre decyzje.

### Przygotowanie do kodowania: Identyfikowanie materiału źródłowego i framerate

Zanim w ogóle zaczniesz myśleć o kodowaniu filmu, musisz przejść kilka wstępnych kroków.

Pierwszym i najważniejszym krokiem przed kodowaniem powinno być ustalenie jakim typem filmu się zajmujesz. Jeśli Twój film jest z DVD albo telewizji (zwykłej, kablowej czy satelitarnej), będzie w jednym z dwóch formatów: NTSC w Ameryce Północnej i Japonii, PAL w Europie itp. Trzeba sobie jednak zdawać sprawę z tego, że jest to tylko format do prezentacji w telewizji, i często nie jest oryginalnym formatem filmu. Doświadczenie pokazuje że filmy NTSC są trudniejsze do kodowania, ponieważ jest więcej elementów do zidentyfikowania w źródle. Żeby zrobić odpowienie kodowanie musisz znać oryginalny format filmu. Nieuwzględnienie tego skutkuje wieloma wadami wynikowego pliku, na przykład brzydkie artefakty przeplotu i powtórzone albo zagubione klatki. Poza tym że są brzydkie, artefakty są też szkodliwe dla kodowania: Dostaniesz gorszą jakość na jednostkę bitrate.

#### Ustalanie źródłowego framerate

Poniżej jest lista popularnych typów materiału źródłowego, gdzie można je najczęściej znaleźć i ich własności:

- Typowy film: Tworzony do wyświetlania przy 24fps.

- Film PAL: Nagrywany kamerą video PAL z prędkością 50 pól na sekundę. Pole składa się tylko z parzystych albo nieparzystych linii klatki. Telewizja była projektowana by odświerzać je naprzemiennie, w charakterze taniej formy analogowej kompresji. Ludzkie oko podobno kompensuje ten efekt, ale jeśli zrozumiesz przeplot nauczysz się go widzieć też w telewizji i nigdy już nie będziesz z niej ZADOWOLONY. Dwa pola nie dają pełnej klatki, ponieważ są uchwycone co 1/50 sekundy, więc nie pasują do siebie, chyba że nie ma ruchu.

- Film NTSC: Nagrany kamerą NTSC z prędkością 60000/1001 pól na sekundę, albo 60 pól na sekundę w erze przedkolorowej. Poza tym podobny do PAL.

- Animacja: Zazwyczaj rysowana przy 24fps, ale zdarzają się też z mieszanym framerate.

- Grafika komputerowa (CG): Może być dowolny framerate, ale niektóre są częstsze niż inne; wartości 24 i 30 klatek na sekundę są typowe dla NTSC, a 25fps jest typowe dla PAL.

- Stary film: Rozmaite niższe framerate.

#### Identyfikowanie materiału źródłowego

Filmy składające się z klatek nazywa się progresywnymi, podczas gdy te składające się z niezależnych pól nazywa się z przeplotem, albo filmem - chociaż ten drugi termin jest niejasny.

Żeby nie było za łatwo, niektóre filmy są kombinacją kilku powyższych typów.

Najważniejszą różnicą między tymi formatami, jest to że niektóre są oparte na klatkach a inne na polach. Zawsze gdy film jest przygotowywany do wyświetlania w telewizji jest przekształcany na format oparty na polach. Rozliczne metody którymi się tego dokonuje są wspólnie nazywane "telecine", a niesławne "3:2 pulldown" z NTSC jest jednym z jego rodzajów. Jeżeli oryginał nie był też oparty na polach (z tą samą prędkością), dostajesz film w innym formacie niż oryginał.

##### Jest kilka popularnych typów pulldown:

- pulldown PAL 2:2: Najprzyjemniejszy z nich wszystkich. Każda klatka jest pokazywana przez czas dwóch pól, poprzez wydobycie parzystych i nieparzystych linii i pokazywanie ich na przemian. Jeśli oryginalny materiał miał 24fps, ten proces przyspiesza film o 4%.

- pulldown PAL 2:2:2:2:2:2:2:2:2:2:2:3: Każda 12ta klatka jest pokazywana przez czas trzech pól zamiast tylko dwóch. Dzięki temu nie ma przyspieszenia o 4%, ale proces jest o wiele trudniejszy do odtworzenia. Zazwyczaj występuje w produkcjach muzycznych, gdzie zmiana prędkości o 4% poważnie by uszkodziła muzykę.

- NTSC 3:2 telecine: Klatki są pokazywane na przemian przez czas 3ch albo 2ch pól. To daje częstotliwość pól 2.5 raza większą niż oryginalna częstotliwość klatek. Rezultat jest też lekko zwolniony z 60 pól na sekundę do 60000/1001 pól na sekundę by utrzymać częstotliwość pól w NTSC.

- NTSC 2:2 pulldown: Używane do pokazywania materiałów 30fps na NTSC. Przyjemne, tak jak pulldown 2:2 PAL.

Są też metody konwersji między filmami PAL i NTSC, ale ten temat wykracza poza zakres tego podręcznika. Jeśli natkniesz się na taki film i chcesz go zakodować, to największe szanse masz robiąc kopię w oryginalnym formacie. Konwersja między tymi dwoma formatami jest wysoce destrukcyjna i nie może zostać ładnie odwrócona, więc kodowanie będzie o wiele gorszej jakości jeśli jest robione z przekonwertowanego źródła.

Gdy film jest zapisywany na DVD, kolejne pary pól są zapisywane jako klatka, pomimo tego że nie są przezaczone do wyświetlania razem. Standard MPEG-2 używany na DVD i w cyfrowej TV pozwala na zakodowanie oryginalnej progresywnej klatki i na przechowanie w nagłówku klatki ilości pól przez które ta klatka powinna być pokazana. Filmy zrobione przy użyciu tej metody są często określane mianem "miękkiego telecine" (soft-telecine), ponieważ proces ten tylko informuje odtwarzacz że ma on zastosować pulldown, a nie stosuje go samemu. Tak jest o wiele lepiej, ponieważ może to zostać łatwo odwrócone (a tak na prawdę zignorowane) przez koder i ponieważ zachowuje możliwie najwyższą jakość. Niestety, wielu producentów DVD i stacji nadawczych nie stosuje prawidłowych technik kodowania ale w zamian produkuje filmy przy użyciu "twardego telecine" (hard-telecine), gdzie pola są faktycznie powtórzone w zakodowanym MPEG-2.

Procedury radzenia sobie z takimi przypadkami będą omówione w dalszej części przewodnika. Teraz podamy tylko kilka wskazówek jak identyfikować z jakim typem materiału mamy do czynienia.

##### Regiony NTSC:

- Jeśli MPlayer wyświetla w trakcie oglądania filmu że framerate zostało zmienione na 24000/1001 i nigdy nie powraca, to jest to prawie na pewno progresywny materiał na którym zastosowano "miękkie telecine".

- Jeśli MPlayer pokazuje że framerate zmienia się między 24000/1001 i 30000/1001 i czasami widzisz "grzebienie" to jest kilka możliwości. Kawałki 24000/1001fps są prawie na pewno progresywne, poddane "miękkiemu telecine", ale fragmenty 30000/1001 fps mogą albo być 24000/1001 poddanym "twardemu telecine" albo filmem NTCS o 60000/1001 polach na sekundę. Używaj tych samych metod co w następnych dwóch przypadkach żeby je odróżnić.

- Jeśli MPlayer nigdy nie pokazuje informacji o zmianie framerate i każda klatka z ruchem wygląda jak grzebień, to masz film NTSC z 60000/1001 polami na sekundę.

- Jeśli MPlayer nigdy nie pokazuje informacji o zmianie framerate i dwie klatki z każdych pięciu mają grzebienie, to film jest 24000/1001 fps poddanym "twardemu telecine".

##### Regiony PAL:

- Jeśli nie widzisz grzebieni, to jest to 2:2 pulldown.

- Jeśli na przemian przez pół sekundy widzisz grzebienie a potem nie, to masz 2:2:2:2:2:2:2:2:2:2:2:3 pulldown.

- Jeśli zawsze widzisz grzebienie w trakcie ruchu, to film jest filmem PAL wyświetlanym z 50 polami na sekundę.

##### Podpowiedź:

MPlayer może zwolnić odtwarzanie filmu opcją -speed albo odtwarzać klatka po klatce. Spróbuj użyć opcji `-speed` 0.2 żeby oglądać film bardzo wolno, albo naciskaj wielokrotnie klawisz "." żeby wyświetlać klatka po klatce. Może to pomóc zidentyfikować wzorzec jeśli nie możesz go dostrzec przy pełnej prędkości.

### Stały kwantyzator a tryb wieloprzebiegowy

Jest możliwe zakodowanie filmu z szeroką gamą jakości. Z nowoczesnymi koderami i odrobiną kompresji przed kodekiem (zmniejszenie rozdzielczości i usuwanie szumu), możliwe jest osiągnięcie bardzo dobrej jakości przy 700 MB, dla 90-110 minutowego filmu kinowego. Dodatkowo tylko najdłuższe filmy nie dają się zakodować na 1400 MB z prawie doskonałą jakością.

Są trzy podejścia do kodowania video: stały bitrate (CBR), stały kwantyzator i tryb wieloprzebiegowy (ABR, uśrednione bitrate).

Złożoność klatek filmu, a zatem i ilość bitów potrzebna na ich zakodowanie, może się bardzo mocno zmieniać w zależności od sceny. Nowoczesne kodery potrafią się dostosowywać do tych zmian i zmieniać bitrate. Jednak w prostych trybach, takich jak CBR, kodery nie znają zapotrzebowania na bitrate w przyszłych scenach, więc nie mogą na długo przekraczać wymaganego bitrate. Bardziej zaawansowane tryby, takie jak kodowanie wieloprzebiegowe, potrafią wziąć pod uwagę statystyki z poprzednich przebiegów, co naprawia ten problem.

#### Uwaga:

Większość kodeków obsługujących kodowanie ABR obsługuje tylko kodowanie dwuprzebiegowe, podczas gdy niektóre inne, na przykład x264 albo Xvid potrafią wykonywać wiele przebiegów, z lekką poprawą jakości po każdym przebiegu. Jednak ta poprawa nie jest zauważalna ani mierzalna po około 4tym przebiegu. Dlatego też, w tej części, tryb dwuprzebiegowy i wieloprzebiegowy będą używane zamiennie.

W każdym z tych trybów, kodek video (na przykład libavcodec) dzieli klatkę obrazu na makrobloki 16x16 pikseli i stosuje do każdego z nich kwantyzator. Im niższy kwantyzator, tym lepsza jakość i tym wyższe bitrate. Metody jakiej koder używa do ustalenia kwantyzatora są różne i można nimi sterować. (Jest to straszliwe uproszczenie, ale wystarcza do zrozumienia podstaw.)

Kiedy podajesz stałe bitrate, kodek koduje usuwając tyle szczegółów ile musi i tak mało jak to tylko możliwe żeby pozostać poniżej podanego bitrate. Jeśli na prawdę nie obchodzi cię wielkość pliku, możesz użyć CBR i podać nieskończone bitrate (W praktyce oznacza to bitrate na tyle wysokie że nie stanowi bariery, na przykład 10000Kbit.) Bez żadnego ograniczenia na bitrate kodek użyje najniższego możliwego kwantyzatora do każdej klatki (ustalonego dla libavcodec opcją `vqmin`, domyślnie 2). Gdy tylko podasz bitrate na tyle niskie że kodek musi używać wyższego kwantyzatora, to prawie na pewno niszczysz film. Żeby tego uniknąć, powinieneś pewnie zmniejszyć rozdzielczość filmu, metodą opisaną dalej. Ogólnie, jeśli zależy Ci na jakości, powinieneś unikać CBR.

Przy stałym kwantyzatorze, kodek używa na każdym makrobloku tego samego kwantyzatora, podanego opcją `vqscale` (w przypadku libavcodec). Jeśli chcesz możliwie najlepszy efekt, znów ignorując bitrate, możesz użyć `vqscale=2`. Da to ten sam bitrate i PSNR (peak signal-to-noise ratio, szczytowa proporcja sygnału do szumu) co CBR z `vbitrate`=nieskończoność i domyślnym `vqmin`.

Problemem przy stałym kwantyzatorze jest to, że używa podanego kwantyzatora niezależnie od tego czy makroblok tego wymaga czy nie. To znaczy że można by było zastosować do makrobloku wyższy kwantyzator bez utraty postrzegalnej jakości. Dlaczego marnować bity na niepotrzebnie niski kwantyzator? Mikroprocesor ma tyle cykli ile jest czasu, ale jest tylko ograniczona ilość bitów na twardym dysku.

Przy kodowaniu dwuprzebiegowym, pierwszy przebieg potraktuje film jak przu ustawieniu CBR, ale zachowa informacje o własnościach każdej klatki. Te dane są później używane przy drugim przebiegu do podejmowania słusznych decyzji o używanym kwantyzatorze. Przy szybkich scenach albo niewielu szczegółach pewnie użyje większego kwantyzatora, podczas gdy dla powolnych, szczegółowych scen będzie niższy kwantyzator.

Jeśli używasz `vqscale=2` to marnujesz bity. Jeśli używasz `vqscale=3` to nie dostajesz najlepszej możliwej jakości. Załóżmy że zakodowałeś swoje DVD przy `vqscale=3` i dostałeś bitrate 1800Kbit. Jeśli zrobisz dwa przebiegi z `vbitrate=1800` ostateczny wynik będzie miał wyższą jakość przy tym samym bitrate.

Ponieważ jesteś już przekonany że prawidłowym wyborem są dwa przebiegi, prawdziwym pytaniem jest jakiego bitrate użyć. Nie ma jednej odpowiedzi. Idealnie chcesz wybrać bitrate będący najlepszym kompromisem między jakością a wielkością pliku. To się zmienia w zależności od filmu.

Jeśli wielkość nie ma znaczenia, dobrym punktem wyjściowym do bardzo wysokiej jakości jest około 2000Kbit plus minus 200Kbit. Jeśli jest dużo akcji albo szczegółów, albo po prostu masz bardzo wrażliwe oko, możesz się zdecydować na 2400 albo 2600. Przy niektórych DVD możesz nie zauważyć różnicy przy 1400Kbit. Dobrym pomysłem jest poeksperymentowanie z kilkoma scenami i różnymi wartościami bitrate żeby nabrać wyczucia.

Jeśli chcesz konkretnej wielkości, musisz jakoś obliczyć bitrare. Ale zanim to zrobisz, musisz wiedzieć ile miejsca potrzebujesz na dźwięk, więc powinieneś ściągnąć go najpierw. Możesz wyliczyć bitrate z następującego równania: bitrate = (wielkość_docelowa_w_MBajtach - wielkość_dźwięku_w_MBajtach) * 1024 * 1024 / długość_w_sekundach * 8 / 1000 Na przykład by wcisnąć dwugodzinny film na płytkę 702MB, z 60MB ścieżki dźwiękowej, bitrate video musi być: (702 - 60) * 1024 * 1024 / (120*60) * 8 / 1000 = 740kbps

### Ograniczenia efektywnego kodowania

Ze względu na naturę kodowania typu MPEG istnieją różne ograniczenia których warto się trzymać żeby osiągnąć najlepszą jakość. MPEG dzieli obraz na kwadraty 16x16 pikseli nazywane makroblokami, każdy z nich składa się z 4 bloków 8x8 informacji o jasności (luminancja, luma) i dwóch 8x8 z połową rozdzielczości (jeden na składową czerwono-morską, drugi na niebiesko-żółtą). Nawet jeśli wysokość i szerokość filmu nie są wielokrotnościami 16, koder użyje tyle makrobloków żeby przykryć cały obszar obrazu, dodatkowa przestrzeń zostanie zmarnowana. Zatem w interesie zwiększenai jakości przy utrzymaniu wielkości pliku kiepskim pomysłem jest używanie wymiarów które nie są wielokrotnością 16.

Większość DVD ma też jakieś czarne ramki na brzegach. Zostawienie ich tam mocno zaszkodzi jakości na kilka sposobów.

1. Kompresje typu MPEG są zależne od transformat przestrzeni częstotliwości, a dokładniej Dyskretnej Transformaty Cosinusowej (DCT), która jest podobna do transformaty Fouriera. Ten sposób kodowania jest efektywny przy wzorach i gładkich przejściach, ale kiepsko sobie radzi z ostrymi krawędziami. Żeby je zakoować, musi używać o wiele większej liczby bitów, albo wystąpią artefakty znane jako pierścienie.

   Transformacja częstotliwości (DCT) jest stosowana osobno do każdego makrobloku (tak na prawdę do każdego bloku), więc ten problem istnieje tylko gdy ostra krawędź jest wewnątrz bloku. Jeśli czarna ramka zaczyna się dokładnie na krawędzi 16-pikselowego bloku, nie stwarza problemów. Jednakże, rzadko kiedy takie ramki są ładnie wyrównane, więc zazwyczaj będzie trzeba przyciąć obraz żeby tego uniknąć.

Poza transformatami przestrzeni częstotliwości, kompresje typu MPEG używają wektorów ruchu, by reprezentować zmiany między sąsiednimi klatkami. Oczywiście wektory ruchu są mniej efektywne w stosunku do nowej treści przychodzącej z brzegów obrazka, ponieważ nie było jej na poprzedniej klatce. Jeśli obraz rozciąga się do krawędzi zakodowanego regionu, wektory ruchu radzą sobie z treścią wychodzącą poza krawędzie. Jednak jeśli są ramki, mogą być kłopoty:

1. Dla każdego makrobloku, kompresja typu MPEG przechowuje wektor opisujący która część poprzedniej klatki powinna być skopiowana do tego makrobloku jako podstawa do przewidzenia następnej klatki. Zakodowane wtedy muszą być tylko różnice. Jeśli makroblok zawiera fragment ramki, to wektory ruchu z pozostałych cześci obrazu zamażą obramowanie. Oznacza to że dużo bitów będzie zużytych albo na jej powtórne zaczernienie albo (co bardziej prawdopodobne), wektor ruchu w ogóle nie będzie użyty i wszystkie zmiany w tym makrobloku będzie trzeba zakodować bezpośrednio. W obu przypadkach, bardzo cierpi na tym efektywność kodowania.

   Powtórnie, ten problem występuje tylko jeśli ramki nie są na krawędziach 16-pikselowych bloków.

2. W końcu, przypuśćmy że mamy makroblok wewnątrz obrazu i obiekt dostaje się do niego z okolic krawędzi. Kodowanie typu MPEG nie potrafi powiedzieć "skopiuj część która jeest wewnątrz obraka, ale nie czarne obramowanie." Dlatego obramowanie też zostanie skopiowane i trzeba będzie zużyć sporo bitów żeby zakodować fragment obrazu który powinien tam być.

   Jeśli obraz sięga do krawędzi zakodowanego obszaru, MPEG ma specjalne optymalizacje do wielokrotnego kopiowania ostatniego rzędu pikseli jeśli wektor ruchu przychodzi z poza zakodoanego obszaru. Staje się to bezużyteczne gry obraz ma czarne obramowanie. W odróżnieniu od problemów 1 i 2 tutaj nic nie pomoże ustawienie obramowania w odpowiednim miejscu.

3. Mimo tego, że obramowanie jest całkowicie czarne i nigdy się nie zmienia, zawsze jest pewien narzut związany z większą ilością makrobloków.

Ze wszystkich tych powodów zalecane jest całkowite wycięcie czarnych obramowań. Dodatkowo, jeśli przy krawędziach jest obszar zakłóceń/zniekształceń, obcięcie go również poprawi efektywność kodowania. Puryści, którzy chcą możliwie dokładnie zachować oryginał mogą się sprzeciwiać, ale jeśli nie planujesz używać stałego kwantyzatora to jakość uzyskana dzięki skadrowaniu znacząco przewyższy utratę informacji przy brzegach.

### Kadrowanie i skalowanie

Przypomnijmy z poprzedniej części że ostateczna wielkość (wysokość i szerokość) obrazu do kodowania powinna być wielokrotnością 16. Można to osiągnąć kadrowaniem, skalowaniem albo kombinacją obydwu.

Przy kadrowaniu, jest kilka reguł których musimy przestrzegać by uniknąć uszkodzenia filmu. Zwykły format YUV, 4:2:0, przechowuje wartości koloru podpróbkowane, czyli kolor jest próbkowany o połowę rzadziej w każdym kierunku niż jasność. Spójrzmy na diagram, na którym L oznacza punkty próbkowania jasności (luma) a C koloru (chroma).

L | L | L | L | L | L | L | L
C | C | C | C
L | L | L | L | L | L | L | L
L | L | L | L | L | L | L | L
C | C | C | C
L | L | L | L | L | L | L | L

Jak widać, wiersze i kolumny obrazu w sposób naturalny łączą się w pary. Dlatego przesunięcia i wymiary kadrowania muszą być liczbami parzystymi. Jeśli nie są, barwa nie będzie już dobrze dopasowana do jasności. Teoretycznie możliwe jest kadrowanie z nieparzystym przesunięciem, ale wymaga to przepróbkowania kolorów, co jest potencjalnie stratną operacją nie obsługiwaną przez filtr kadrowania.

Dalej, film z przeplotem jest kodowany jak poniżej:

Górne pole | Dolne pole
L | L | L | L | L | L | L | L |  |  |  |  |  |  |  |
C | C | C | C |  |  |  |  |  |  |  |
|  |  |  |  |  |  |  | L | L | L | L | L | L | L | L
L | L | L | L | L | L | L | L |  |  |  |  |  |  |  |
|  |  |  |  |  |  |  | C | C | C | C
|  |  |  |  |  |  |  | L | L | L | L | L | L | L | L
L | L | L | L | L | L | L | L |  |  |  |  |  |  |  |
C | C | C | C |  |  |  |  |  |  |  |
|  |  |  |  |  |  |  | L | L | L | L | L | L | L | L
L | L | L | L | L | L | L | L |  |  |  |  |  |  |  |
|  |  |  |  |  |  |  | C | C | C | C
|  |  |  |  |  |  |  | L | L | L | L | L | L | L | L

Jak widać, wzór powtarza się dopiero po 4 liniach. Dlatego przy filmie z przeplotem, pionowa współrzędna i wysokość kadrowania muszą być wielokrotnościami 4.

Podstawową rozdzielczością DVD jest 720x480 dla NTSC i 720x576 dla PAL, ale jest też flaga proporcji, która określa czy obraz jest ekranowy (4:3) czy panoramiczny (16:9). Wiele (jeśli nie większość) panoramicznych DVD nie jest dokładnie 16:9 tylko raczej 1,85:1 lub 2,35:1 (cinescope). Oznacza to że będzie czarne obramowanie na filmie, które trzeba usunąć.

MPlayer dostarcza filtr wykrywania kadrowania (`-vf cropdetect`), który określi prostokąt kadrowania. Uruchom MPlayera z opcją `-vf cropdetect` a wydrukuje on ustawienia kadrowania potrzebne do usunięcia obramowania. Powinieneś puścić film wystarczająco długo żeby został użyty cały obszar obrazu, inaczej wartości będą niedokładne.

Potem przetestuj otrzymane wartości z użyciem MPlayera, przekazując opcje podane przez `cropdetect` i dostosowując prostokąt według potrzeb. Filtr `rectangle` może w tym pomóc, pozwalając na interaktywne ustawienie prostokąta kadrowania na filmie. Pamiętaj, by trzymać się powyższych reguł podzielności, żeby nie przestawić płaszczyzny koloru.

W pewnych przypadkach skalowanie może być niepożądane. Skalowanie w kierunku pionowym jest trudne przy filmie z przeplotem, a jeśli chcesz zachować przeplot, zazwyczaj powinieneś się wstrzymać od skalowania. Jeśl nie chcesz skalować, ale nadal chcesz używać wymiarów będących wielokrotnościami 16 to musisz przekadrować. NIe należy niedokadrowywać, bo obramowania są bardzo szkodliwe przy kodowaniu!

Ponieważ MPEG-4 używa makrobloków 16x16, powinieneś się upewnić, że każdy wymiar kodowanego filmu jest wielokrotnością 16, inaczej degradujemy jakość, zwłaszcza przy niższych bitrate. Można tego dokonać zaokrąglając wysokość i szerokość prostokąta kadrowania do najbliższej wielokrotności 16. Jak powiedziano wcześniej, trzeba zwiększyć przesunięcie pionowe o połowę różnicy między starą a nową wysokością, żeby wynikowy film był brany ze środka klatki. A ze względu na sposób w jaki próbkowane jest DVD, upewnij się że przesunięcie jest parzyste (w zasadzie, stosuj się do reguły, żeby nigdy nie używać nieparzystych wartości przy przycinaniu i skalowaniu obrazu). Jeśli nie czujesz się dobrze odrzucając dodatkowe piksele, może wolisz przeskalować video. Przyjżymy się temu w przykładzie poniżej. Możesz też pozwolić filtrowi `cropdetect` zrobić to wszystko za Ciebie, jako że ma on opcjonalny parametr `round` (zaokrąglenie), domyślnie równy 16.

Uważaj też na "poł-czarne" piksele na przegach. Też je wykadruj, albo będziesz na nie marnował bity któ?e przydadzą się gdzie indziej.

Po tym wszystkim prawdopodobnie dostaniesz film który nie ma dokładnie proporcji 1,85:1 ani 2,35:1 tylko coś podobnego. Mógłbyś samemu policzyć nowe proporcje, ale MEncoder ma pocję do libavcodec nazywaną `autoaspect` która zrobi to za Ciebie. Nie powinieneś przeskalowywać video żeby wyrównać piksele, chyba że chcesz marnować miejsce na dysku. Skalowanie powinno być robione przy odtwarzaniu, a odtwarzacz używa informacji o proporcjach zapisanych w AVI żeby określić prawidłową rozdzielczość. Niestety, nie wszystkie odtwarzacze uznają te informacje, dlatego mimo wszystko możesz chcieć przeskalować.

### Dobieranie rozdzielczości i bitrate

Jeśli nie kodujesz w trybie stałego kwantyzatora, musisz wybrać bitrate. Jest to dość prosta rzecz – to (średnia) ilość bitów jaka będzie używana do zakodowania jednej sekundy filmu. Zazwyczaj bitrate mierzy się w kilobitach (1000 bitów) na sekundę. Wielkość filmu na dysku to bitrate razy długość filmu, plus drobne "dodatki" (patrz na przykład sekcja o kontenerze AVI ). Pozostałe parametry, takie jak skalowanie, kadrowanie itp. nie zmienią wielkości pliku jeśli nie zmienisz też bitrate!

Bitrate nie skaluje się proporcjonalnie do rozdzielczości. To znaczy, film 320x240 w 200 kbit/s nie będzie tej samej jakości co ten sam film w 640x480 i 800 kbit/s! Są ku temu dwie przyczyny:

1. Wizualna: Łatwiej zauważyć artefakty MPEG jeśli są bardziej powiększone! Artefakty powstają na poziomie bloków (8x8). Ludzkie oko trudniej dostrzega błędy w 4800 małych blokach niż w 1200 dużych (zakładając że skalujesz na pełny ekran).

2. Teoretyczna: Kiedy zmniejszasz obraz ale nadal używasz tych samych bloków 8x8 do transformacji przestrzeni częstotliwości. masz więcej danych w pasmach wyższych częstotliwości. W pewien sposób każdy piksel ma więcej szczegółów niż poprzednio. Dlatego, mimo że przeskalowany obraz zawiera 1/4 informacji jeśli chodzi o wielkość, to nadal może zawierać większość informacji w przestrzeni częstotliwości (zakładając że wysokie częstotliwości były mało używane w oryginalnym filmie 640x480).

Poprzednie podręczniki zalecały dobranie bitrate i rozdzielczości w sposób bazujący na podejściu "bity na piksel", ale z powyższych powodów zazwyczaj nie jest to prawidłowe. Lepszym przybliżeniem zdaje się skalowanie bitrate proporcjonalnie do pierwiastka kwadratowego z rozdzielczości, czyli film 320x240 i 400 kbit/s powinien być podobny do 640x480 i 800 kbit/s. Nie zostało to jednak zweryfikowane ani teoretycznie ani empirycznie. Dodatkowo, ponieważ filmy są bardzo zróżnicowane jeśli chodzi o szum, szczegóły, ilość ruchu itp. bezsensowne jest podawanie ogólnych zaleceń na bity na przekątą (analogia bitów na piksel używająca pierwiastka).

Omówiliśmy więc problemy z wyborem bitrate i rozdzielczości.

#### Obliczanie rozdzielczości

Następne kroki przeprowadzą Cię przez obliczenie rozdzielczości dla Twojego filmu bez zniekształcania go za bardzo, biorąc pod uwagę kilka typów informacji o źródłowym filmie. Najpierw powinieneś policzyć zakodowane proporcje: ARc = (Wc x (ARa / PRdvd )) / Hc

##### gdzie:

- Hc i Wc to wysokość i szerokość skadrowanego filmu.

- ARa do wyświetlane proporcje, zazwyczaj 4/3 lub 16/9.

- PRdvd to proporcje na DVD równe 1,25=(720*576) dla DVD PAL i 1,5=(720/480) dla VD NTSC.

Potem możesz policzyć rozdzielczość X i Y, zgodnie z dobranym wskażnikiem Jakości Kompresji (Compression Quality, CQ): RozY = INT(Pierw( 1000*Bitrate/25/ARc/CQ )/16) * 16 i RozX = INT( ResY * ARc / 16) * 16, gdzie INT oznacza zaokrąglenie do liczby całkowitej.

Dobrze, ale co to jest CQ? CQ reprezentuje ilość bitów na piksel i klatkę kodowania. Z grubsza biorąc, im większe CQ tym mniejsza szansa na zobaczenie artefaktów kodowania. Jednakże, jeśli masz docelową wielkość filmu (na przykład 1 lub 2 płyty CD), masz ograniczoną ilość bitów do zużycia; dlatego musisz znaleźć równowagę między poziomem kompresji i jakością.

CQ zależy od bitrate, efektywności kodeka video i rozdzielczości filmu. Żeby podnieść CQ zazwyczej zmniejszysz film, ponieważ bitrate jest funkcją docelowej wielkości i długości filmu, które są stałe. Przy użyciu kodeków MPEG-4 ASP, takich jak Xvid i libavcodec, CQ niższe niż 0,18 zazwyczaj daje kiepski obraz, ponieważ nie ma dość bitów by zakodować informacje z każdego makrobloku. (MPEG4, jak wiele innych kodeków, grupuje piksele w bloki żeby skompresować obraz. Jeśli nie ma dość bitów widać krawędzie tych bloków.) Dlatego też mądrze jest wybrać CQ w zakresie 0,20 do 0,22 na film jednopłytkowy i 0,26-0,28 na dwupłytkowy przy standardowych opcjach kodowania. Bardziej zaawansowane opcje kodowania, takie jak te podane tutaj dla libavcodec i Xvid powinny umożliwić otrzymanie takiej samej jakości z CQ w zakresie 0,18 do 0,20 na 1 CD i 0,24 do 0,26 na 2 CD. Z kodekami MPEG-4 AVC, takimi jak x264, możesz używać CQ w zakresie 0,14 do 0,16 przy standardowych opcjach a powinno się też udać zejść do 0,10 do 0,12 z zaawansowanymi opcjami kodowania x264.

Pamiętajmy, że CQ jest tylko przydatnym odnośnikiem, zależnym od kodowanego filmu. CQ równe ,018 może wyglądać dobrze przy Bergmanie, w przeciwieństwie do filmu takiego jak Martix, który zaawiera wiele bardzo ruchliwych scen. Z drugiej strony, bezsensowne jest podnoszenie CQ powyżej 0,30 jako że marnuje się bity bez zauważalnej poprawy jakości. Pamiętajmy też że, jak było wspomniane wcześniej, filmy w niższej rozdzielczości potrzebują większego CQ (w porównaniu do na przykład rozdzielczości DVD) żeby dobrze wyglądać.

### Filtrowanie

Bardzo ważne do robienia dobrych kodowań jest nauczenie się posługiwania systemem filtrów MEncodera. Całe przetwarzanie video jest wykonywane przez filtry – kadrowanie, skalowanie, dopasowywanie kolorów, usuwanie szumu, telecine, odwrócone telecine, usuwanie bloków żeby wymienić choć część. Poza dużą ilością obsługiwanych formatów wejściowych to właśnie zakres dostępnych filtrów jest jedną z głównych przewag MEncodera nad podobnymi programami.

Filtry są ładowane do łańcucha przy pomocy opcji -vf:

    -vf filtr1=opcje,filtr2=opcje,...

Większość filtrów przyjmuje kilka parametrów numerycznych oddzielanych dwukropkami, ale dokładna składnia zależy od filtru więc szczegóły odnośnie filtrów, które chcesz zastosować, znajdziesz na stronie man.

Filtry działają na filmie w kolejnoścy w jakiej zostały załadowane. Na przykład następujący łańcuch:

    -vf crop=688:464:12:4,scale=640:464

najpierw skadruje fragment 688x464 filmu z lewym górnym rogiem na pozycji (12,4) a potem zmniejszy rozdzielczość wyniku do 640x464.

Niektóre filtry trzeba ładować na początku lub blisko początku łańcucha, ponieważ korzystają one z informacji którą następne filtry mogą zgubić lub unieważnić. Sztandarowym przykłądem jest `pp` (postprocessing, tylko gdy wykonuje operacje usuwania bloków lub pierścieni), `spp` (inny postprocessor do usuwania artefaktów MPEG), `pullup` (odwrócone telecine) i `softpulldown` (konwertuje miękkie telecine na twarde).

W ogólności chcesz przeprowadzać jak najmniej filtrowania żeby film pozostał możliwie bliski oryginałowi. Kadrowanie często jest niezbęne (jak opisano powyżej) ale staraj się uniknąć skalowania. Chociaż czasami zmniejszenie rozdzielczości jest lepszym wyjściem niż użycie wyższego kwantyzatora, chcemy uniknąć obu: pamiętajmy, że od początku zdecydowaliśmy się wybrać jakość kosztem wielkości.

Nie należy też dostosowywać gammy, kontrastu, jasności itp. Co wygląda dobrze na Twoim ekranie może nie być tak dobre na innych. Takie dostrojenia powinny być wykonywane tylko przy odtwarzaniu.

Jedną rzeczą którą możesz chcieć zrobić, jest przepuszczenie filmu przez bardzo lekkie usuwanie szumów, takie jak `-vf hqdn3d=2:1:2`. Znów, to kwestia lepszego zastosowania bitów: po co marnować je na zakodowanie szumu skoro można dodać ten szum przy odtwarzaniu? Zwiększenie parametrów dla `hqdn3d` jeszcze bardziej poprawi kompresowalność, ale jeśli przesadzisz to zauważalnie zniekształcisz obraz. Wartości sugerowane powyżej (`2:1:2`) są dość konserwatywne; nie bój się eksperymentować z wyższymi wartościami i samemu oceniać wyniki.

### Przeplot i telecine

Prawie wszystkie filmy są kręcone przy 24 fps. Ponieważ NTSC ma 30000/1001 fps potrzebna jest pewna przeróbka żeby film 24 fps mógł być wyświetlany z prawidłową szybkością NTSC. Ten proces nazywa się 3:2 pulldown, często zwany też telecine (ponieważ jest używany przy konwersji z kina do telewizji) i, w uproszczeniu, jest to spowolnienie filmu do 24000/1001 fps i powtórzenie co czwartej klatki.

Filmy DVD PAL, odtwarzanie przy 25 fps, nie wymagają żadnego specjalnego traktowania. (Technicznie rzecz ujmując, PAL może być poddany telecine, nazywanemu 2:2 pulldown, ale w praktyce nie jest to problemem.) Po prostu film 24 fps jest odtwarzany przy 25 fps. W wyniku tego film jest odtwarzany odrobinkę szybciej, ale jeśli nie masz nieziemskich zmysłów to tego nie zauważysz. Większość DVD PAL ma skorygowaną wysokość dźwięku, więc kiedy są odtwarzane przy 25 fps dźwięk będzie brzmiał poprawnie, mimo tego że ścieżka dźwiekowa (jak i cały film) jest o 4% krótsza niż DVD NTSC.

Ponieważ film na DVD PAL nie został zmieniony, nie ma powodu za bardzo przejmować się framerate. Oryginał ma 25 fps i Twój rip też będzie miał 25 fps. Jednak jeśli ripujesz film z DVD NTSC możesz być zmuszony do zastosowania odwrotnego telecine.

Dla filmów nagrywanych przy 24 fps obraz na DVD NTSC jest albo poddany telecine na 30000/1001 albo jest progresywny przy 24000/1001 i przeznaczony do poddania telecine w locie przez odtwarzacz DVD. Z drugiej strony seriale telewizyjne zazwyczaj mają tylko przeplot, nie są poddane telecine. Nie jest to reguła: Niektóre seriale (na przykład Buffy Łowca Wampirów) mają przeplot, a inne są mieszanką progresywnego i przeplotu (Angel, 24).

Jest wysoce zalecane żebyś przeczytał sekcję How to deal with telecine and interlacing in NTSC DVDs żeby dowiedzieć się jak sobie radzić z różnymi możliwościami.

Jednak jeśli zazwyczaj tylko ripujesz filmy, prawdopodobnie masz doczynienia z filmem 24 fps progresywnym lub poddanym telecine, a w takim przypadku możesz użyć filtra `pullup` podając parametr `-vf pullup,softskip`.

### Encoding interlaced video

If the movie you want to encode is interlaced (NTSC video or PAL video), you will need to choose whether you want to deinterlace or not. While deinterlacing will make your movie usable on progressive scan displays such a computer monitors and projectors, it comes at a cost: The fieldrate of 50 or 60000/1001 fields per second is halved to 25 or 30000/1001 frames per second, and roughly half of the information in your movie will be lost during scenes with significant motion.

Therefore, if you are encoding for high quality archival purposes, it is recommended not to deinterlace. You can always deinterlace the movie at playback time when displaying it on progressive scan devices. The power of currently available computers forces players to use a deinterlacing filter, which results in a slight degradation in image quality. But future players will be able to mimic the interlaced display of a TV, deinterlacing to full fieldrate and interpolating 50 or 60000/1001 entire frames per second from the interlaced video.

Special care must be taken when working with interlaced video:

1. Crop height and y-offset must be multiples of 4.

2. Any vertical scaling must be performed in interlaced mode.

3. Postprocessing and denoising filters may not work as expected unless you take special care to operate them a field at a time, and they may damage the video if used incorrectly.

With these things in mind, here is our first example:

    mencoder capture.avi -mc 0 -oac lavc -ovc lavc -lavcopts \
        vcodec=mpeg2video:vbitrate=6000:ilme:ildct:acodec=mp2:abitrate=224

Note the `ilme` and `ildct` options.

### Notes on Audio/Video synchronization

MEncoder's audio/video synchronization algorithms were designed with the intention of recovering files with broken sync. However, in some cases they can cause unnecessary skipping and duplication of frames, and possibly slight A/V desync, when used with proper input (of course, A/V sync issues apply only if you process or copy the audio track while transcoding the video, which is strongly encouraged). Therefore, you may have to switch to basic A/V sync with the `-mc 0` option, or put this in your ~/.mplayer/mencoder config file, as long as you are only working with good sources (DVD, TV capture, high quality MPEG-4 rips, etc) and not broken ASF/RM/MOV files.

If you want to further guard against strange frame skips and duplication, you can use both `-mc 0` and `-noskip`. This will prevent all A/V sync, and copy frames one-to-one, so you cannot use it if you will be using any filters that unpredictably add or drop frames, or if your input file has variable framerate! Therefore, using `-noskip` is not in general recommended.

The so-called "three-pass" audio encoding which MEncoder supports has been reported to cause A/V desync. This will definitely happen if it is used in conjunction with certain filters, therefore, it is now recommended not to use three-pass audio mode. This feature is only left for compatibility purposes and for expert users who understand when it is safe to use and when it is not. If you have never heard of three-pass mode before, forget that we even mentioned it!

There have also been reports of A/V desync when encoding from stdin with MEncoder. Do not do this! Always use a file or CD/DVD/etc device as input.

### Choosing the video codec

Which video codec is best to choose depends on several factors, like size, quality, streamability, usability and popularity, some of which widely depend on personal taste and technical constraints.

- Compression efficiency: It is quite easy to understand that most newer-generation codecs are made to increase quality and compression. Therefore, the authors of this guide and many other people suggest that you cannot go wrong Be careful, however: Decoding DVD-resolution MPEG-4 AVC videos requires a fast machine (i.e. a Pentium 4 over 1.5GHz or a Pentium M over 1GHz). when choosing MPEG-4 AVC codecs like x264 instead of MPEG-4 ASP codecs such as libavcodec MPEG-4 or Xvid. (Advanced codec developers may be interested in reading Michael Niedermayer's opinion on "why MPEG4-ASP sucks".) Likewise, you should get better quality using MPEG-4 ASP than you would with MPEG-2 codecs.

  However, newer codecs which are in heavy development can suffer from bugs which have not yet been noticed and which can ruin an encode. This is simply the tradeoff for using bleeding-edge technology.

  What is more, beginning to use a new codec requires that you spend some time becoming familiar with its options, so that you know what to adjust to achieve a desired picture quality.

- Hardware compatibility: It usually takes a long time for standalone video players to begin to include support for the latest video codecs. As a result, most only support MPEG-1 (like VCD, XVCD and KVCD), MPEG-2 (like DVD, SVCD and KVCD) and MPEG-4 ASP (like DivX, libavcodec's LMP4 and Xvid) (Beware: Usually, not all MPEG-4 ASP features are supported). Please refer to the technical specs of your player (if they are available), or google around for more information.

- Best quality per encoding time: Codecs that have been around for some time (such as libavcodec MPEG-4 and Xvid) are usually heavily optimized with all kinds of smart algorithms and SIMD assembly code. That is why they tend to yield the best quality per encoding time ratio. However, they may have some very advanced options that, if enabled, will make the encode really slow for marginal gains.

  If you are after blazing speed you should stick around the default settings of the video codec (although you should still try the other options which are mentioned in other sections of this guide).

  You may also consider choosing a codec which can do multi-threaded processing, though this is only useful for users of machines with several CPUs. libavcodec MPEG-4 does allow that, but speed gains are limited, and there is a slight negative effect on picture quality. Xvid's multi-threaded encoding, activated by the `threads` option, can be used to boost encoding speed — by about 40-60% in typical cases — with little if any picture degradation. x264 also allows multi-threaded encoding, which currently speeds up encoding by 94% per CPU core while lowering PSNR between 0.005dB and 0.01dB on a typical setup.

- Personal taste: This is where it gets almost irrational: For the same reason that some hung on to DivX 3 for years when newer codecs were already doing wonders, some folks will prefer Xvid or libavcodec MPEG-4 over x264.

  You should make your own judgement; do not take advice from people who swear by one codec. Take a few sample clips from raw sources and compare different encoding options and codecs to find one that suits you best. The best codec is the one you master, and the one that looks best to your eyes on your display The same encode may not look the same on someone else's monitor or when played back by a different decoder, so future-proof your encodes by playing them back on different setups. !

Please refer to the section selecting codecs and container formats to get a list of supported codecs.

### Audio

Audio is a much simpler problem to solve: if you care about quality, just leave it as is. Even AC-3 5.1 streams are at most 448Kbit/s, and they are worth every bit. You might be tempted to transcode the audio to high quality Vorbis, but just because you do not have an A/V receiver for AC-3 pass-through today does not mean you will not have one tomorrow. Future-proof your DVD rips by preserving the AC-3 stream. You can keep the AC-3 stream either by copying it directly into the video stream during the encoding. You can also extract the AC-3 stream in order to mux it into containers such as NUT or Matroska.

    mplayer source_file.vob -aid 129 -dumpaudio -dumpfile sound.ac3

will dump into the file sound.ac3 the audio track number 129 from the file source_file.vob (NB: DVD VOB files usually use a different audio numbering, which means that the VOB audio track 129 is the 2nd audio track of the file).

But sometimes you truly have no choice but to further compress the sound so that more bits can be spent on the video. Most people choose to compress audio with either MP3 or Vorbis audio codecs. While the latter is a very space-efficient codec, MP3 is better supported by hardware players, although this trend is changing.

Do not use `-nosound` when encoding a file with audio, even if you will be encoding and muxing audio separately later. Though it may work in ideal cases, using `-nosound` is likely to hide some problems in your encoding command line setting. In other words, having a soundtrack during your encode assures you that, provided you do not see messages such as Too many audio packets in the buffer, you will be able to get proper sync.

You need to have MEncoder process the sound. You can for example copy the original soundtrack during the encode with `-oac copy` or convert it to a "light" 4 kHz mono WAV PCM with `-oac pcm -channels 1 -srate 4000`. Otherwise, in some cases, it will generate a video file that will not sync with the audio. Such cases are when the number of video frames in the source file does not match up to the total length of audio frames or whenever there are discontinuities/splices where there are missing or extra audio frames. The correct way to handle this kind of problem is to insert silence or cut audio at these points. However MPlayer cannot do that, so if you demux the AC-3 audio and encode it with a separate app (or dump it to PCM with MPlayer), the splices will be left incorrect and the only way to correct them is to drop/duplicate video frames at the splice. As long as MEncoder sees the audio when it is encoding the video, it can do this dropping/duping (which is usually OK since it takes place at full black/scene change), but if MEncoder cannot see the audio, it will just process all frames as-is and they will not fit the final audio stream when you for example merge your audio and video track into a Matroska file.

First of all, you will have to convert the DVD sound into a WAV file that the audio codec can use as input. For example:

    mplayer source_file.vob -ao pcm:file=destination_sound.wav \
        -vc dummy -aid 1 -vo null

will dump the second audio track from the file source_file.vob into the file destination_sound.wav. You may want to normalize the sound before encoding, as DVD audio tracks are commonly recorded at low volumes. You can use the tool normalize for instance, which is available in most distributions. If you are using Windows, a tool such as BeSweet can do the same job. You will compress in either Vorbis or MP3. For example:

    oggenc -q1 destination_sound.wav

will encode destination_sound.wav with the encoding quality 1, which is roughly equivalent to 80Kb/s, and is the minimum quality at which you should encode if you care about quality. Please note that MEncoder currently cannot mux Vorbis audio tracks into the output file because it only supports AVI and MPEG containers as an output, each of which may lead to audio/video playback synchronization problems with some players when the AVI file contain VBR audio streams such as Vorbis. Do not worry, this document will show you how you can do that with third party programs.

### Muxing

Now that you have encoded your video, you will most likely want to mux it with one or more audio tracks into a movie container, such as AVI, MPEG, Matroska or NUT. MEncoder is currently only able to natively output audio and video into MPEG and AVI container formats. for example:

    mencoder -oac copy -ovc copy  -o output_movie.avi \
        -audiofile input_audio.mp2 input_video.avi

This would merge the video file input_video.avi and the audio file input_audio.mp2 into the AVI file output_movie.avi. This command works with MPEG-1 layer I, II and III (more commonly known as MP3) audio, WAV and a few other audio formats too.

MEncoder features experimental support for libavformat, which is a library from the FFmpeg project that supports muxing and demuxing a variety of containers. For example:

    mencoder -oac copy -ovc copy -o output_movie.asf -audiofile input_audio.mp2 \
        input_video.avi -of lavf -lavfopts format=asf

This will do the same thing as the previous example, except that the output container will be ASF. Please note that this support is highly experimental (but getting better every day), and will only work if you compiled MPlayer with the support for libavformat enabled (which means that a pre-packaged binary version will not work in most cases).

#### Improving muxing and A/V sync reliability

You may experience some serious A/V sync problems while trying to mux your video and some audio tracks, where no matter how you adjust the audio delay, you will never get proper sync. That may happen when you use some video filters that will drop or duplicate some frames, like the inverse telecine filters. It is strongly encouraged to append the `harddup` video filter at the end of the filter chain to avoid this kind of problem.

Without `harddup`, if MEncoder wants to duplicate a frame, it relies on the muxer to put a mark on the container so that the last frame will be displayed again to maintain sync while writing no actual frame. With `harddup`, MEncoder will instead just push the last frame displayed again into the filter chain. This means that the encoder receives the exact same frame twice, and compresses it. This will result in a slightly bigger file, but will not cause problems when demuxing or remuxing into other container formats.

You may also have no choice but to use `harddup` with container formats that are not too tightly linked with MEncoder such as the ones supported through libavformat, which may not support frame duplication at the container level.

#### Limitations of the AVI container

Although it is the most widely-supported container format after MPEG-1, AVI also has some major drawbacks. Perhaps the most obvious is the overhead. For each chunk of the AVI file, 24 bytes are wasted on headers and index. This translates into a little over 5 MB per hour, or 1-2.5% overhead for a 700 MB movie. This may not seem like much, but it could mean the difference between being able to use 700 kbit/sec video or 714 kbit/sec, and every bit of quality counts.

In addition this gross inefficiency, AVI also has the following major limitations:

1. Only fixed-fps content can be stored. This is particularly limiting if the original material you want to encode is mixed content, for example a mix of NTSC video and film material. Actually there are hacks that can be used to store mixed-framerate content in AVI, but they increase the (already huge) overhead fivefold or more and so are not practical.

2. Audio in AVI files must be either constant-bitrate (CBR) or constant-framesize (i.e. all frames decode to the same number of samples). Unfortunately, the most efficient codec, Vorbis, does not meet either of these requirements. Therefore, if you plan to store your movie in AVI, you will have to use a less efficient codec such as MP3 or AC-3.

Having said all that, MEncoder does not currently support variable-fps output or Vorbis encoding. Therefore, you may not see these as limitations if MEncoder is the only tool you will be using to produce your encodes. However, it is possible to use MEncoder only for video encoding, and then use external tools to encode audio and mux it into another container format.

#### Muxing into the Matroska container

Matroska is a free, open standard container format, aiming to offer a lot of advanced features, which older containers like AVI cannot handle. For example, Matroska supports variable bitrate audio content (VBR), variable framerates (VFR), chapters, file attachments, error detection code (EDC) and modern A/V Codecs like "Advanced Audio Coding" (AAC), "Vorbis" or "MPEG-4 AVC" (H.264), next to nothing handled by AVI.

The tools required to create Matroska files are collectively called mkvtoolnix, and are available for most Unix platforms as well as Windows. Because Matroska is an open standard you may find other tools that suit you better, but since mkvtoolnix is the most common, and is supported by the Matroska team itself, we will only cover its usage.

Probably the easiest way to get started with Matroska is to use MMG, the graphical frontend shipped with mkvtoolnix, and follow the guide to mkvmerge GUI (mmg)

You may also mux audio and video files using the command line:

    mkvmerge -o output.mkv input_video.avi input_audio1.mp3 input_audio2.ac3

This would merge the video file input_video.avi and the two audio files input_audio1.mp3 and input_audio2.ac3 into the Matroska file output.mkv. Matroska, as mentioned earlier, is able to do much more than that, like multiple audio tracks (including fine-tuning of audio/video synchronization), chapters, subtitles, splitting, etc... Please refer to the documentation of those applications for more details.

## How to deal with telecine and interlacing within NTSC DVDs

### Introduction

#### What is telecine?

If you do not understand much of what is written in this document, read the Wikipedia entry on telecine. It is an understandable and reasonably comprehensive description of what telecine is.

#### A note about the numbers.

Many documents, including the article linked above, refer to the fields per second value of NTSC video as 59.94 and the corresponding frames per second values as 29.97 (for telecined and interlaced) and 23.976 (for progressive). For simplicity, some documents even round these numbers to 60, 30, and 24.

Strictly speaking, all those numbers are approximations. Black and white NTSC video was exactly 60 fields per second, but 60000/1001 was later chosen to accommodate color data while remaining compatible with contemporary black and white televisions. Digital NTSC video (such as on a DVD) is also 60000/1001 fields per second. From this, interlaced and telecined video are derived to be 30000/1001 frames per second; progressive video is 24000/1001 frames per second.

Older versions of the MEncoder documentation and many archived mailing list posts refer to 59.94, 29.97, and 23.976. All MEncoder documentation has been updated to use the fractional values, and you should use them too.

`-ofps 23.976` is incorrect. `-ofps 24000/1001` should be used instead.

#### How telecine is used.

All video intended to be displayed on an NTSC television set must be 60000/1001 fields per second. Made-for-TV movies and shows are often filmed directly at 60000/1001 fields per second, but the majority of cinema is filmed at 24 or 24000/1001 frames per second. When cinematic movie DVDs are mastered, the video is then converted for television using a process called telecine.

On a DVD, the video is never actually stored as 60000/1001 fields per second. For video that was originally 60000/1001, each pair of fields is combined to form a frame, resulting in 30000/1001 frames per second. Hardware DVD players then read a flag embedded in the video stream to determine whether the odd- or even-numbered lines should form the first field.

Usually, 24000/1001 frames per second content stays as it is when encoded for a DVD, and the DVD player must perform telecining on-the-fly. Sometimes, however, the video is telecined before being stored on the DVD; even though it was originally 24000/1001 frames per second, it becomes 60000/1001 fields per second. When it is stored on the DVD, pairs of fields are combined to form 30000/1001 frames per second.

When looking at individual frames formed from 60000/1001 fields per second video, telecined or otherwise, interlacing is clearly visible wherever there is any motion, because one field (say, the even-numbered lines) represents a moment in time 1/(60000/1001) seconds later than the other. Playing interlaced video on a computer looks ugly both because the monitor is higher resolution and because the video is shown frame-after-frame instead of field-after-field.

#### Notes:

- This section only applies to NTSC DVDs, and not PAL.

- The example MEncoder lines throughout the document are not intended for actual use. They are simply the bare minimum required to encode the pertaining video category. How to make good DVD rips or fine-tune libavcodec for maximal quality is not within the scope of this section; refer to other sections within the MEncoder encoding guide.

- There are a couple footnotes specific to this guide, linked like this: [1]

### How to tell what type of video you have

#### Progressive

Progressive video was originally filmed at 24000/1001 fps, and stored on the DVD without alteration.

When you play a progressive DVD in MPlayer, MPlayer will print the following line as soon as the movie begins to play:

    demux_mpg: 24000/1001 fps progressive NTSC content detected, switching framerate.

From this point forward, demux_mpg should never say it finds "30000/1001 fps NTSC content."

When you watch progressive video, you should never see any interlacing. Beware, however, because sometimes there is a tiny bit of telecine mixed in where you would not expect. I have encountered TV show DVDs that have one second of telecine at every scene change, or at seemingly random places. I once watched a DVD that had a progressive first half, and the second half was telecined. If you want to be really thorough, you can scan the entire movie:

    mplayer dvd://1 -nosound -vo null -benchmark

Using `-benchmark` makes MPlayer play the movie as quickly as it possibly can; still, depending on your hardware, it can take a while. Every time demux_mpg reports a framerate change, the line immediately above will show you the time at which the change occurred.

Sometimes progressive video on DVDs is referred to as "soft-telecine" because it is intended to be telecined by the DVD player.

#### Telecined

Telecined video was originally filmed at 24000/1001, but was telecined before it was written to the DVD.

MPlayer does not (ever) report any framerate changes when it plays telecined video.

Watching a telecined video, you will see interlacing artifacts that seem to "blink": they repeatedly appear and disappear. You can look closely at this by

1.     mplayer dvd://1

2. Seek to a part with motion.

3. Use the . key to step forward one frame at a time.

4. Look at the pattern of interlaced-looking and progressive-looking frames. If the pattern you see is PPPII,PPPII,PPPII,... then the video is telecined. If you see some other pattern, then the video may have been telecined using some non-standard method; MEncoder cannot losslessly convert non-standard telecine to progressive. If you do not see any pattern at all, then it is most likely interlaced.

Sometimes telecined video on DVDs is referred to as "hard-telecine". Since hard-telecine is already 60000/1001 fields per second, the DVD player plays the video without any manipulation.

Another way to tell if your source is telecined or not is to play the source with the `-vf pullup` and `-v` command line options to see how `pullup` matches frames. If the source is telecined, you should see on the console a 3:2 pattern with 0+.1.+2 and 0++1 alternating. This technique has the advantage that you do not need to watch the source to identify it, which could be useful if you wish to automate the encoding procedure, or to carry out said procedure remotely via a slow connection.

#### Interlaced

Interlaced video was originally filmed at 60000/1001 fields per second, and stored on the DVD as 30000/1001 frames per second. The interlacing effect (often called "combing") is a result of combining pairs of fields into frames. Each field is supposed to be 1/(60000/1001) seconds apart, and when they are displayed simultaneously the difference is apparent.

As with telecined video, MPlayer should not ever report any framerate changes when playing interlaced content.

When you view an interlaced video closely by frame-stepping with the . key, you will see that every single frame is interlaced.

#### Mixed progressive and telecine

All of a "mixed progressive and telecine" video was originally 24000/1001 frames per second, but some parts of it ended up being telecined.

When MPlayer plays this category, it will (often repeatedly) switch back and forth between "30000/1001 fps NTSC" and "24000/1001 fps progressive NTSC". Watch the bottom of MPlayer's output to see these messages.

You should check the "30000/1001 fps NTSC" sections to make sure they are actually telecine, and not just interlaced.

#### Mixed progressive and interlaced

In "mixed progressive and interlaced" content, progressive and interlaced video have been spliced together.

This category looks just like "mixed progressive and telecine", until you examine the 30000/1001 fps sections and see that they do not have the telecine pattern.

### How to encode each category

As I mentioned in the beginning, example MEncoder lines below are not meant to actually be used; they only demonstrate the minimum parameters to properly encode each category.

#### Progressive

Progressive video requires no special filtering to encode. The only parameter you need to be sure to use is `-ofps 24000/1001`. Otherwise, MEncoder will try to encode at 30000/1001 fps and will duplicate frames.

    mencoder dvd://1 -oac copy -ovc lavc -ofps 24000/1001

It is often the case, however, that a video that looks progressive actually has very short parts of telecine mixed in. Unless you are sure, it is safest to treat the video as mixed progressive and telecine. The performance loss is small [3].

#### Telecined

Telecine can be reversed to retrieve the original 24000/1001 content, using a process called inverse-telecine. MPlayer contains several filters to accomplish this; the best filter, `pullup`, is described in the mixed progressive and telecine section.

#### Interlaced

For most practical cases it is not possible to retrieve a complete progressive video from interlaced content. The only way to do so without losing half of the vertical resolution is to double the framerate and try to "guess" what ought to make up the corresponding lines for each field (this has drawbacks - see method 3).

1. Encode the video in interlaced form. Normally, interlacing wreaks havoc with the encoder's ability to compress well, but libavcodec has two parameters specifically for dealing with storing interlaced video a bit better: `ildct` and `ilme`. Also, using `mbd=2` is strongly recommended [2] because it will encode macroblocks as non-interlaced in places where there is no motion. Note that `-ofps` is NOT needed here.

       mencoder dvd://1 -oac copy -ovc lavc -lavcopts ildct:ilme:mbd=2

2. Use a deinterlacing filter before encoding. There are several of these filters available to choose from, each with its own advantages and disadvantages. Consult `mplayer -pphelp` and `mplayer -vf help` to see what is available (grep for "deint"), read Michael Niedermayer's Deinterlacing filters comparison, and search the MPlayer mailing lists to find many discussions about the various filters. Again, the framerate is not changing, so no `-ofps`. Also, deinterlacing should be done after cropping [1] and before scaling.

       mencoder dvd://1 -oac copy -vf yadif -ovc lavc

3. Unfortunately, this option is buggy with MEncoder; it ought to work well with MEncoder G2, but that is not here yet. You might experience crashes. Anyway, the purpose of `-vf tfields` is to create a full frame out of each field, which makes the framerate 60000/1001. The advantage of this approach is that no data is ever lost; however, since each frame comes from only one field, the missing lines have to be interpolated somehow. There are no very good methods of generating the missing data, and so the result will look a bit similar to when using some deinterlacing filters. Generating the missing lines creates other issues, as well, simply because the amount of data doubles. So, higher encoding bitrates are required to maintain quality, and more CPU power is used for both encoding and decoding. tfields has several different options for how to create the missing lines of each frame. If you use this method, then Reference the manual, and chose whichever option looks best for your material. Note that when using `tfields` you have to specify both `-fps` and `-ofps` to be twice the framerate of your original source.

       mencoder dvd://1 -oac copy -vf tfields=2 -ovc lavc \
           -fps 60000/1001 -ofps 60000/1001

4. If you plan on downscaling dramatically, you can extract and encode only one of the two fields. Of course, you will lose half the vertical resolution, but if you plan on downscaling to at most 1/2 of the original, the loss will not matter much. The result will be a progressive 30000/1001 frames per second file. The procedure is to use `-vf field`, then crop [1] and scale appropriately. Remember that you will have to adjust the scale to compensate for the vertical resolution being halved.

       mencoder dvd://1 -oac copy -vf field=0 -ovc lavc

#### Mixed progressive and telecine

In order to turn mixed progressive and telecine video into entirely progressive video, the telecined parts have to be inverse-telecined. There are three ways to accomplish this, described below. Note that you should always inverse-telecine before any rescaling; unless you really know what you are doing, inverse-telecine before cropping, too [1]. `-ofps 24000/1001` is needed here because the output video will be 24000/1001 frames per second.

- `-vf pullup` is designed to inverse-telecine telecined material while leaving progressive data alone. In order to work properly, `pullup` must be followed by the `softskip` filter or else MEncoder will crash. `pullup` is, however, the cleanest and most accurate method available for encoding both telecine and "mixed progressive and telecine".

      mencoder dvd://1 -oac copy -vf pullup,softskip
          -ovc lavc -ofps 24000/1001

- `-vf filmdint` is similar to `-vf pullup`: both filters attempt to match a pair of fields to form a complete frame. `filmdint` will deinterlace individual fields that it cannot match, however, whereas `pullup` will simply drop them. Also, the two filters have separate detection code, and `filmdint` may tend to match fields a bit less often. Which filter works better may depend on the input video and personal taste; feel free to experiment with fine-tuning the filters' options if you encounter problems with either one (see the man page for details). For most well-mastered input video, however, both filters work quite well, so either one is a safe choice to start with.

      mencoder dvd://1 -oac copy -vf filmdint -ovc lavc -ofps 24000/1001

- An older method is to, rather than inverse-telecine the telecined parts, telecine the non-telecined parts and then inverse-telecine the whole video. Sound confusing? softpulldown is a filter that goes through a video and makes the entire file telecined. If we follow softpulldown with either `detc` or `ivtc`, the final result will be entirely progressive. `-ofps 24000/1001` is needed.

      mencoder dvd://1 -oac copy -vf softpulldown,ivtc=1 -ovc lavc -ofps 24000/1001

#### Mixed progressive and interlaced

There are two options for dealing with this category, each of which is a compromise. You should decide based on the duration/location of each type.

- Treat it as progressive. The interlaced parts will look interlaced, and some of the interlaced fields will have to be dropped, resulting in a bit of uneven jumpiness. You can use a postprocessing filter if you want to, but it may slightly degrade the progressive parts.

  This option should definitely not be used if you want to eventually display the video on an interlaced device (with a TV card, for example). If you have interlaced frames in a 24000/1001 frames per second video, they will be telecined along with the progressive frames. Half of the interlaced "frames" will be displayed for three fields' duration (3/(60000/1001) seconds), resulting in a flicking "jump back in time" effect that looks quite bad. If you even attempt this, you must use a deinterlacing filter like `lb` or `l5`.

  It may also be a bad idea for progressive display, too. It will drop pairs of consecutive interlaced fields, resulting in a discontinuity that can be more visible than with the second method, which shows some progressive frames twice. 30000/1001 frames per second interlaced video is already a bit choppy because it really should be shown at 60000/1001 fields per second, so the duplicate frames do not stand out as much.

  Either way, it is best to consider your content and how you intend to display it. If your video is 90% progressive and you never intend to show it on a TV, you should favor a progressive approach. If it is only half progressive, you probably want to encode it as if it is all interlaced.

- Treat it as interlaced. Some frames of the progressive parts will need to be duplicated, resulting in uneven jumpiness. Again, deinterlacing filters may slightly degrade the progressive parts.

### Footnotes

1. #### About cropping:

   Video data on DVDs are stored in a format called YUV 4:2:0. In YUV video, luma ("brightness") and chroma ("color") are stored separately. Because the human eye is somewhat less sensitive to color than it is to brightness, in a YUV 4:2:0 picture there is only one chroma pixel for every four luma pixels. In a progressive picture, each square of four luma pixels (two on each side) has one common chroma pixel. You must crop progressive YUV 4:2:0 to even resolutions, and use even offsets. For example, `crop=716:380:2:26` is OK but `crop=716:380:3:26` is not.

   When you are dealing with interlaced YUV 4:2:0, the situation is a bit more complicated. Instead of every four luma pixels in the frame sharing a chroma pixel, every four luma pixels in each field share a chroma pixel. When fields are interlaced to form a frame, each scanline is one pixel high. Now, instead of all four luma pixels being in a square, there are two pixels side-by-side, and the other two pixels are side-by-side two scanlines down. The two luma pixels in the intermediate scanline are from the other field, and so share a different chroma pixel with two luma pixels two scanlines away. All this confusion makes it necessary to have vertical crop dimensions and offsets be multiples of four. Horizontal can stay even.

   For telecined video, I recommend that cropping take place after inverse telecining. Once the video is progressive you only need to crop by even numbers. If you really want to gain the slight speedup that cropping first may offer, you must crop vertically by multiples of four or else the inverse-telecine filter will not have proper data.

   For interlaced (not telecined) video, you must always crop vertically by multiples of four unless you use `-vf field` before cropping.

2. #### About encoding parameters and quality:

   Just because I recommend `mbd=2` here does not mean it should not be used elsewhere. Along with `trell`, `mbd=2` is one of the two libavcodec options that increases quality the most, and you should always use at least those two unless the drop in encoding speed is prohibitive (e.g. realtime encoding). There are many other options to libavcodec that increase encoding quality (and decrease encoding speed) but that is beyond the scope of this document.

3. #### About the performance of pullup:

   It is safe to use `pullup` (along with `softskip` ) on progressive video, and is usually a good idea unless the source has been definitively verified to be entirely progressive. The performance loss is small for most cases. On a bare-minimum encode, `pullup` causes MEncoder to be 50% slower. Adding sound processing and advanced `lavcopts` overshadows that difference, bringing the performance decrease of using `pullup` down to 2%.

## Encoding with the libavcodec codec family

libavcodec provides simple encoding to a lot of interesting video and audio formats. You can encode to the following codecs (more or less up to date):

### libavcodec's video codecs

Video codec name | Description
--- | ---
mjpeg | Motion JPEG
ljpeg | lossless JPEG
jpegls | JPEG LS
targa | Targa image
gif | GIF image
bmp | BMP image
png | PNG image
h261 | H.261
h263 | H.263
h263p | H.263+
mpeg4 | ISO standard MPEG-4 (DivX, Xvid compatible)
msmpeg4 | pre-standard MPEG-4 variant by MS, v3 (AKA DivX3)
msmpeg4v2 | pre-standard MPEG-4 by MS, v2 (used in old ASF files)
wmv1 | Windows Media Video, version 1 (AKA WMV7)
wmv2 | Windows Media Video, version 2 (AKA WMV8)
rv10 | RealVideo 1.0
rv20 | RealVideo 2.0
mpeg1video | MPEG-1 video
mpeg2video | MPEG-2 video
huffyuv | lossless compression
ffvhuff | FFmpeg modified huffyuv lossless
asv1 | ASUS Video v1
asv2 | ASUS Video v2
ffv1 | FFmpeg's lossless video codec
svq1 | Sorenson video 1
flv | Sorenson H.263 used in Flash Video
flashsv | Flash Screen Video
dvvideo | Sony Digital Video
snow | FFmpeg's experimental wavelet-based codec
zmbv | Zip Motion Blocks Video
dnxhd | AVID DNxHD

The first column contains the codec names that should be passed after the `vcodec` config, like: `-lavcopts vcodec=msmpeg4`

An example with MJPEG compression:

    mencoder dvd://2 -o title2.avi -ovc lavc -lavcopts vcodec=mjpeg -oac copy

### libavcodec's audio codecs

Audio codec name | Description
--- | ---
ac3 | Dolby Digital (AC-3)
adpcm_* | Adaptive PCM formats - see supplementary table
flac | Free Lossless Audio Codec (FLAC)
g726 | G.726 ADPCM
libamr_nb | 3GPP Adaptive Multi-Rate (AMR) narrow-band
libamr_wb | 3GPP Adaptive Multi-Rate (AMR) wide-band
libfaac | Advanced Audio Coding (AAC) - using FAAC
libgsm | ETSI GSM 06.10 full rate
libgsm_ms | Microsoft GSM
libmp3lame | MPEG-1 audio layer 3 (MP3) - using LAME
mp2 | MPEG-1 audio layer 2 (MP2)
pcm_* | PCM formats - see supplementary table
roq_dpcm | Id Software RoQ DPCM
sonic | experimental FFmpeg lossy codec
sonicls | experimental FFmpeg lossless codec
vorbis | Vorbis
wmav1 | Windows Media Audio v1
wmav2 | Windows Media Audio v2

The first column contains the codec names that should be passed after the `acodec` option, like: `-lavcopts acodec=ac3`

An example with AC-3 compression:

    mencoder dvd://2 -o title2.avi -oac lavc -lavcopts acodec=ac3 -ovc copy

Contrary to libavcodec's video codecs, its audio codecs do not make a wise usage of the bits they are given as they lack some minimal psychoacoustic model (if at all) which most other codec implementations feature. However, note that all these audio codecs are very fast and work out-of-the-box everywhere MEncoder has been compiled with libavcodec (which is the case most of time), and do not depend on external libraries.

#### PCM/ADPCM format supplementary table

PCM/ADPCM codec name | Description
--- | ---
pcm_s32le | signed 32-bit little-endian
pcm_s32be | signed 32-bit big-endian
pcm_u32le | unsigned 32-bit little-endian
pcm_u32be | unsigned 32-bit big-endian
pcm_s24le | signed 24-bit little-endian
pcm_s24be | signed 24-bit big-endian
pcm_u24le | unsigned 24-bit little-endian
pcm_u24be | unsigned 24-bit big-endian
pcm_s16le | signed 16-bit little-endian
pcm_s16be | signed 16-bit big-endian
pcm_u16le | unsigned 16-bit little-endian
pcm_u16be | unsigned 16-bit big-endian
pcm_s8 | signed 8-bit
pcm_u8 | unsigned 8-bit
pcm_alaw | G.711 A-LAW
pcm_mulaw | G.711 μ-LAW
pcm_s24daud | signed 24-bit D-Cinema Audio format
pcm_zork | Activision Zork Nemesis
adpcm_ima_qt | Apple QuickTime
adpcm_ima_wav | Microsoft/IBM WAVE
adpcm_ima_dk3 | Duck DK3
adpcm_ima_dk4 | Duck DK4
adpcm_ima_ws | Westwood Studios
adpcm_ima_smjpeg | SDL Motion JPEG
adpcm_ms | Microsoft
adpcm_4xm | 4X Technologies
adpcm_xa | Phillips Yellow Book CD-ROM eXtended Architecture
adpcm_ea | Electronic Arts
adpcm_ct | Creative 16->4-bit
adpcm_swf | Adobe Shockwave Flash
adpcm_yamaha | Yamaha
adpcm_sbpro_4 | Creative VOC SoundBlaster Pro 8->4-bit
adpcm_sbpro_3 | Creative VOC SoundBlaster Pro 8->2.6-bit
adpcm_sbpro_2 | Creative VOC SoundBlaster Pro 8->2-bit
adpcm_thp | Nintendo GameCube FMV THP
adpcm_adx | Sega/CRI ADX

### Encoding options of libavcodec

Ideally, you would probably want to be able to just tell the encoder to switch into "high quality" mode and move on. That would probably be nice, but unfortunately hard to implement as different encoding options yield different quality results depending on the source material. That is because compression depends on the visual properties of the video in question. For example, Anime and live action have very different properties and thus require different options to obtain optimum encoding. The good news is that some options should never be left out, like `mbd=2`, `trell`, and `v4mv`. See below for a detailed description of common encoding options.

#### Options to adjust:

- vmax_b_frames: 1 or 2 is good, depending on the movie. Note that if you need to have your encode be decodable by DivX5, you need to activate closed GOP support, using libavcodec's `cgop` option, but you need to deactivate scene detection, which is not a good idea as it will hurt encode efficiency a bit.

- vb_strategy=1: helps in high-motion scenes. On some videos, vmax_b_frames may hurt quality, but vmax_b_frames=2 along with vb_strategy=1 helps.

- dia: motion search range. Bigger is better and slower. Negative values are a completely different scale. Good values are -1 for a fast encode, or 2-4 for slower.

- predia: motion search pre-pass. Not as important as dia. Good values are 1 (default) to 4. Requires preme=2 to really be useful.

- cmp, subcmp, precmp: Comparison function for motion estimation. Experiment with values of 0 (default), 2 (hadamard), 3 (dct), and 6 (rate distortion). 0 is fastest, and sufficient for precmp. For cmp and subcmp, 2 is good for Anime, and 3 is good for live action. 6 may or may not be slightly better, but is slow.

- last_pred: Number of motion predictors to take from the previous frame. 1-3 or so help at little speed cost. Higher values are slow for no extra gain.

- cbp, mv0: Controls the selection of macroblocks. Small speed cost for small quality gain.

- qprd: adaptive quantization based on the macroblock's complexity. May help or hurt depending on the video and other options. This can cause artifacts unless you set vqmax to some reasonably small value (6 is good, maybe as low as 4); vqmin=1 should also help.

- qns: very slow, especially when combined with qprd. This option will make the encoder minimize noise due to compression artifacts instead of making the encoded video strictly match the source. Do not use this unless you have already tweaked everything else as far as it will go and the results still are not good enough.

- vqcomp: Tweak ratecontrol. What values are good depends on the movie. You can safely leave this alone if you want. Reducing vqcomp puts more bits on low-complexity scenes, increasing it puts them on high-complexity scenes (default: 0.5, range: 0-1. recommended range: 0.5-0.7).

- vlelim, vcelim: Sets the single coefficient elimination threshold for luminance and chroma planes. These are encoded separately in all MPEG-like algorithms. The idea behind these options is to use some good heuristics to determine when the change in a block is less than the threshold you specify, and in such a case, to just encode the block as "no change". This saves bits and perhaps speeds up encoding. vlelim=-4 and vcelim=9 seem to be good for live movies, but seem not to help with Anime; when encoding animation, you should probably leave them unchanged.

- qpel: Quarter pixel motion estimation. MPEG-4 uses half pixel precision for its motion search by default, therefore this option comes with an overhead as more information will be stored in the encoded file. The compression gain/loss depends on the movie, but it is usually not very effective on Anime. qpel always incurs a significant cost in CPU decode time (+25% in practice).

- psnr: does not affect the actual encoding, but writes a log file giving the type/size/quality of each frame, and prints a summary of PSNR (Peak Signal to Noise Ratio) at the end.

#### Options not recommended to play with:

- vme: The default is best.

- lumi_mask, dark_mask: Psychovisual adaptive quantization. You do not want to play with those options if you care about quality. Reasonable values may be effective in your case, but be warned this is very subjective.

- scplx_mask: Tries to prevent blocky artifacts, but postprocessing is better.

### Encoding setting examples

The following settings are examples of different encoding option combinations that affect the speed vs quality tradeoff at the same target bitrate.

All the encoding settings were tested on a 720x448 @30000/1001 fps video sample, the target bitrate was 900kbps, and the machine was an AMD-64 3400+ at 2400 MHz in 64 bits mode. Each encoding setting features the measured encoding speed (in frames per second) and the PSNR loss (in dB) compared to the "very high quality" setting. Please understand that depending on your source, your machine type and development advancements, you may get very different results.

Description | Encoding options | speed (in fps) | Relative PSNR loss (in dB)
--- | --- | --- | ---
Very high quality | `vcodec=mpeg4:mbd=2:mv0:trell:v4mv:cbp:last_pred=3:predia=2:dia=2:vmax_b_frames=2:vb_strategy=1:precmp=2:cmp=2:subcmp=2:preme=2:qns=2` | 6fps | 0dB
High quality | `vcodec=mpeg4:mbd=2:trell:v4mv:last_pred=2:dia=-1:vmax_b_frames=2:vb_strategy=1:cmp=3:subcmp=3:precmp=0:vqcomp=0.6:turbo` | 15fps | -0.5dB
Fast | `vcodec=mpeg4:mbd=2:trell:v4mv:turbo` | 42fps | -0.74dB
Realtime | `vcodec=mpeg4:mbd=2:turbo` | 54fps | -1.21dB

### Custom inter/intra matrices

With this feature of libavcodec you are able to set custom inter (I-frames/keyframes) and intra (P-frames/predicted frames) matrices. It is supported by many of the codecs: mpeg1video and mpeg2video are reported as working.

A typical usage of this feature is to set the matrices preferred by the KVCD specifications.

The KVCD "Notch" Quantization Matrix:

Intra:

     8  9 12 22 26 27 29 34
     9 10 14 26 27 29 34 37
    12 14 18 27 29 34 37 38
    22 26 27 31 36 37 38 40
    26 27 29 36 39 38 40 48
    27 29 34 37 38 40 48 58
    29 34 37 38 40 48 58 69
    34 37 38 40 48 58 69 79

Inter:

    16 18 20 22 24 26 28 30
    18 20 22 24 26 28 30 32
    20 22 24 26 28 30 32 34
    22 24 26 30 32 32 34 36
    24 26 28 32 34 34 36 38
    26 28 30 32 34 36 38 40
    28 30 32 34 36 38 42 42
    30 32 34 36 38 40 42 44

Usage:

    mencoder input.avi -o output.avi -oac copy -ovc lavc \
        -lavcopts inter_matrix=...:intra_matrix=...

    mencoder input.avi -ovc lavc -lavcopts \
    vcodec=mpeg2video:intra_matrix=8,9,12,22,26,27,29,34,9,10,14,26,27,29,34,37,\
    12,14,18,27,29,34,37,38,22,26,27,31,36,37,38,40,26,27,29,36,39,38,40,48,27,\
    29,34,37,38,40,48,58,29,34,37,38,40,48,58,69,34,37,38,40,48,58,69,79\
    :inter_matrix=16,18,20,22,24,26,28,30,18,20,22,24,26,28,30,32,20,22,24,26,\
    28,30,32,34,22,24,26,30,32,32,34,36,24,26,28,32,34,34,36,38,26,28,30,32,34,\
    36,38,40,28,30,32,34,36,38,42,42,30,32,34,36,38,40,42,44 -oac copy -o svcd.mpg

### Example

So, you have just bought your shiny new copy of Harry Potter and the Chamber of Secrets (widescreen edition, of course), and you want to rip this DVD so that you can add it to your Home Theatre PC. This is a region 1 DVD, so it is NTSC. The example below will still apply to PAL, except you will omit `-ofps 24000/1001` (because the output framerate is the same as the input framerate), and of course the crop dimensions will be different.

After running `mplayer dvd://1`, we follow the process detailed in the section How to deal with telecine and interlacing in NTSC DVDs and discover that it is 24000/1001 fps progressive video, which means that we need not use an inverse telecine filter, such as `pullup` or `filmdint`.

Next, we want to determine the appropriate crop rectangle, so we use the cropdetect filter:

    mplayer dvd://1 -vf cropdetect

Make sure you seek to a fully filled frame (such as a bright scene, past the opening credits and logos), and you will see in MPlayer's console output:

    crop area: X: 0..719  Y: 57..419  (-vf crop=720:362:0:58)

We then play the movie back with this filter to test its correctness:

    mplayer dvd://1 -vf crop=720:362:0:58

And we see that it looks perfectly fine. Next, we ensure the width and height are a multiple of 16. The width is fine, however the height is not. Since we did not fail 7th grade math, we know that the nearest multiple of 16 lower than 362 is 352.

We could just use `crop=720:352:0:58`, but it would be nice to take a little off the top and a little off the bottom so that we retain the center. We have shrunk the height by 10 pixels, but we do not want to increase the y-offset by 5-pixels since that is an odd number and will adversely affect quality. Instead, we will increase the y-offset by 4 pixels:

    mplayer dvd://1 -vf crop=720:352:0:62

Another reason to shave pixels from both the top and the bottom is that we ensure we have eliminated any half-black pixels if they exist. Note that if your video is telecined, make sure the `pullup` filter (or whichever inverse telecine filter you decide to use) appears in the filter chain before you crop. If it is interlaced, deinterlace before cropping. (If you choose to preserve the interlaced video, then make sure your vertical crop offset is a multiple of 4.)

If you are really concerned about losing those 10 pixels, you might prefer instead to scale the dimensions down to the nearest multiple of 16. The filter chain would look like:

    -vf crop=720:362:0:58,scale=720:352

Scaling the video down like this will mean that some small amount of detail is lost, though it probably will not be perceptible. Scaling up will result in lower quality (unless you increase the bitrate). Cropping discards those pixels altogether. It is a tradeoff that you will want to consider for each circumstance. For example, if the DVD video was made for television, you might want to avoid vertical scaling, since the line sampling corresponds to the way the content was originally recorded.

On inspection, we see that our movie has a fair bit of action and high amounts of detail, so we pick 2400Kbit for our bitrate.

We are now ready to do the two pass encode. Pass one:

    mencoder dvd://1 -ofps 24000/1001 -oac copy -o Harry_Potter_2.avi -ovc lavc \
        -lavcopts vcodec=mpeg4:vbitrate=2400:v4mv:mbd=2:trell:cmp=3:subcmp=3:autoaspect:vpass=1 \
        -vf pullup,softskip,crop=720:352:0:62,hqdn3d=2:1:2

And pass two is the same, except that we specify `vpass=2`:

    mencoder dvd://1 -ofps 24000/1001 -oac copy -o Harry_Potter_2.avi -ovc lavc \
        -lavcopts vcodec=mpeg4:vbitrate=2400:v4mv:mbd=2:trell:cmp=3:subcmp=3:autoaspect:vpass=2 \
        -vf pullup,softskip,crop=720:352:0:62,hqdn3d=2:1:2

The options `v4mv:mbd=2:trell` will greatly increase the quality at the expense of encoding time. There is little reason to leave these options out when the primary goal is quality. The options `cmp=3:subcmp=3` select a comparison function that yields higher quality than the defaults. You might try experimenting with this parameter (refer to the man page for the possible values) as different functions can have a large impact on quality depending on the source material. For example, if you find libavcodec produces too much blocky artifacts, you could try selecting the experimental NSSE as comparison function via `*cmp=10`.

For this movie, the resulting AVI will be 138 minutes long and nearly 3GB. And because you said that file size does not matter, this is a perfectly acceptable size. However, if you had wanted it smaller, you could try a lower bitrate. Increasing bitrates have diminishing returns, so while we might clearly see an improvement from 1800Kbit to 2000Kbit, it might not be so noticeable above 2000Kbit. Feel free to experiment until you are happy.

Because we passed the source video through a denoise filter, you may want to add some of it back during playback. This, along with the `spp` post-processing filter, drastically improves the perception of quality and helps eliminate blocky artifacts in the video. With MPlayer's `autoq` option, you can vary the amount of post-processing done by the spp filter depending on available CPU. Also, at this point, you may want to apply gamma and/or color correction to best suit your display. For example:

    mplayer Harry_Potter_2.avi -vf spp,noise=9ah:5ah,eq2=1.2 -autoq 3

## Encoding with the Xvid codec

Xvid is a free library for encoding MPEG-4 ASP video streams. Before starting to encode, you need to set up MEncoder to support it.

This guide mainly aims at featuring the same kind of information as x264's encoding guide. Therefore, please begin by reading the first part of that guide.

### What options should I use to get the best results?

Please begin by reviewing the Xvid section of MPlayer's man page. This section is intended to be a supplement to the man page.

The Xvid default settings are already a good tradeoff between speed and quality, therefore you can safely stick to them if the following section puzzles you.

### Encoding options of Xvid

- vhq This setting affects the macroblock decision algorithm, where the higher the setting, the wiser the decision. The default setting may be safely used for every encode, while higher settings always help PSNR but are significantly slower. Please note that a better PSNR does not necessarily mean that the picture will look better, but tells you that it is closer to the original. Turning it off will noticeably speed up encoding; if speed is critical for you, the tradeoff may be worth it.

- bvhq This does the same job as vhq, but does it on B-frames. It has a negligible impact on speed, and slightly improves quality (around +0.1dB PSNR).

- max_bframes A higher number of consecutive allowed B-frames usually improves compressibility, although it may also lead to more blocking artifacts. The default setting is a good tradeoff between compressibility and quality, but you may increase it up to 3 if you are bitrate-starved. You may also decrease it to 1 or 0 if you are aiming at perfect quality, though in that case you should make sure your target bitrate is high enough to ensure that the encoder does not have to increase quantizers to reach it.

- bf_threshold This controls the B-frame sensitivity of the encoder, where a higher value leads to more B-frames being used (and vice versa). This setting is to be used together with `max_bframes`; if you are bitrate-starved, you should increase both `max_bframes` and `bf_threshold`, while you may increase `max_bframes` and reduce `bf_threshold` so that the encoder may use more B-frames in places that only really need them. A low number of `max_bframes` and a high value of `bf_threshold` is probably not a wise choice as it will force the encoder to put B-frames in places that would not benefit from them, therefore reducing visual quality. However, if you need to be compatible with standalone players that only support old DivX profiles (which only supports up to 1 consecutive B-frame), this would be your only way to increase compressibility through using B-frames.

- trellis Optimizes the quantization process to get an optimal tradeoff between PSNR and bitrate, which allows significant bit saving. These bits will in return be spent elsewhere on the video, raising overall visual quality. You should always leave it on as its impact on quality is huge. Even if you are looking for speed, do not disable it until you have turned down `vhq` and all other more CPU-hungry options to the minimum.

- hq_ac Activates a better coefficient cost estimation method, which slightly reduces file size by around 0.15 to 0.19% (which corresponds to less than 0.01dB PSNR increase), while having a negligible impact on speed. It is therefore recommended to always leave it on.

- cartoon Designed to better encode cartoon content, and has no impact on speed as it just tunes the mode decision heuristics for this type of content.

- me_quality This setting is to control the precision of the motion estimation. The higher `me_quality`, the more precise the estimation of the original motion will be, and the better the resulting clip will capture the original motion.

  The default setting is best in all cases; thus it is not recommended to turn it down unless you are really looking for speed, as all the bits saved by a good motion estimation would be spent elsewhere, raising overall quality. Therefore, do not go any lower than 5, and even that only as a last resort.

- chroma_me Improves motion estimation by also taking the chroma (color) information into account, whereas `me_quality` alone only uses luma (grayscale). This slows down encoding by 5-10% but improves visual quality quite a bit by reducing blocking effects and reduces file size by around 1.3%. If you are looking for speed, you should disable this option before starting to consider reducing `me_quality`.

- chroma_opt Is intended to increase chroma image quality around pure white/black edges, rather than improving compression. This can help to reduce the "red stairs" effect.

- lumi_mask Tries to give less bitrate to part of the picture that the human eye cannot see very well, which should allow the encoder to spend the saved bits on more important parts of the picture. The quality of the encode yielded by this option highly depends on personal preferences and on the type and monitor settings used to watch it (typically, it will not look as good if it is bright or if it is a TFT monitor).

- qpel Raise the number of candidate motion vectors by increasing the precision of the motion estimation from halfpel to quarterpel. The idea is to find better motion vectors which will in return reduce bitrate (hence increasing quality). However, motion vectors with quarterpel precision require a few extra bits to code, but the candidate vectors do not always give (much) better results. Quite often, the codec still spends bits on the extra precision, but little or no extra quality is gained in return. Unfortunately, there is no way to foresee the possible gains of `qpel`, so you need to actually encode with and without it to know for sure.

  `qpel` can be almost double encoding time, and requires as much as 25% more processing power to decode. It is not supported by all standalone players.

- gmc Tries to save bits on panning scenes by using a single motion vector for the whole frame. This almost always raises PSNR, but significantly slows down encoding (as well as decoding). Therefore, you should only use it when you have turned `vhq` to the maximum. Xvid's GMC is more sophisticated than DivX's, but is only supported by few standalone players.

### Encoding profiles

Xvid supports encoding profiles through the `profile` option, which are used to impose restrictions on the properties of the Xvid video stream such that it will be playable on anything which supports the chosen profile. The restrictions relate to resolutions, bitrates and certain MPEG-4 features. The following table shows what each profile supports.

| Simple | Advanced Simple | DivX
Profile name | 0 | 1 | 2 | 3 | 0 | 1 | 2 | 3 | 4 | 5 | Handheld | Portable NTSC | Portable PAL | Home Theater NTSC | Home Theater PAL | HDTV
Width [pixels] | 176 | 176 | 352 | 352 | 176 | 176 | 352 | 352 | 352 | 720 | 176 | 352 | 352 | 720 | 720 | 1280
Height [pixels] | 144 | 144 | 288 | 288 | 144 | 144 | 288 | 288 | 576 | 576 | 144 | 240 | 288 | 480 | 576 | 720
Frame rate [fps] | 15 | 15 | 15 | 15 | 30 | 30 | 15 | 30 | 30 | 30 | 15 | 30 | 25 | 30 | 25 | 30
Max average bitrate [kbps] | 64 | 64 | 128 | 384 | 128 | 128 | 384 | 768 | 3000 | 8000 | 537.6 | 4854 | 4854 | 4854 | 4854 | 9708.4
Peak average bitrate over 3 secs [kbps] |  |  |  |  |  |  |  |  |  |  | 800 | 8000 | 8000 | 8000 | 8000 | 16000
Max. B-frames | 0 | 0 | 0 | 0 |  |  |  |  |  |  | 0 | 1 | 1 | 1 | 1 | 2
MPEG quantization |  |  |  |  | X | X | X | X | X | X |  |  |  |  |  |
Adaptive quantization |  |  |  |  | X | X | X | X | X | X | X | X | X | X | X | X
Interlaced encoding |  |  |  |  | X | X | X | X | X | X |  |  |  | X | X | X
Quarterpixel |  |  |  |  | X | X | X | X | X | X |  |  |  |  |  |
Global motion compensation |  |  |  |  | X | X | X | X | X | X |  |  |  |  |  |

### Encoding setting examples

The following settings are examples of different encoding option combinations that affect the speed vs quality tradeoff at the same target bitrate.

All the encoding settings were tested on a 720x448 @30000/1001 fps video sample, the target bitrate was 900kbps, and the machine was an AMD-64 3400+ at 2400 MHz in 64 bits mode. Each encoding setting features the measured encoding speed (in frames per second) and the PSNR loss (in dB) compared to the "very high quality" setting. Please understand that depending on your source, your machine type and development advancements, you may get very different results.

Description | Encoding options | speed (in fps) | Relative PSNR loss (in dB)
--- | --- | --- | ---
Very high quality | `chroma_opt:vhq=4:bvhq=1:quant_type=mpeg` | 16fps | 0dB
High quality | `vhq=2:bvhq=1:chroma_opt:quant_type=mpeg` | 18fps | -0.1dB
Fast | `turbo:vhq=0` | 28fps | -0.69dB
Realtime | `turbo:nochroma_me:notrellis:max_bframes=0:vhq=0` | 38fps | -1.48dB

## Encoding with the x264 codec

x264 is a free library for encoding H.264/AVC video streams. Before starting to encode, you need to set up MEncoder to support it.

### Encoding options of x264

Please begin by reviewing the x264 section of MPlayer's man page. This section is intended to be a supplement to the man page. Here you will find quick hints about which options are most likely to interest most people. The man page is more terse, but also more exhaustive, and it sometimes offers much better technical detail.

#### Introduction

This guide considers two major categories of encoding options:

1. Options which mainly trade off encoding time vs. quality

2. Options which may be useful for fulfilling various personal preferences and special requirements

Ultimately, only you can decide which options are best for your purposes. The decision for the first class of options is the simplest: you only have to decide whether you think the quality differences justify the speed differences. For the second class of options, preferences may be far more subjective, and more factors may be involved. Note that some of the "personal preferences and special requirements" options can still have large impacts on speed or quality, but that is not what they are primarily useful for. A couple of the "personal preference" options may even cause changes that look better to some people, but look worse to others.

Before continuing, you need to understand that this guide uses only one quality metric: global PSNR. For a brief explanation of what PSNR is, see the Wikipedia article on PSNR. Global PSNR is the last PSNR number reported when you include the `psnr` option in `x264encopts`. Any time you read a claim about PSNR, one of the assumptions behind the claim is that equal bitrates are used.

Nearly all of this guide's comments assume you are using two pass. When comparing options, there are two major reasons for using two pass encoding. First, using two pass often gains around 1dB PSNR, which is a very big difference. Secondly, testing options by doing direct quality comparisons with one pass encodes introduces a major confounding factor: bitrate often varies significantly with each encode. It is not always easy to tell whether quality changes are due mainly to changed options, or if they mostly reflect essentially random differences in the achieved bitrate.

#### Options which primarily affect speed and quality

- subq: Of the options which allow you to trade off speed for quality, `subq` and `frameref` (see below) are usually by far the most important. If you are interested in tweaking either speed or quality, these are the first options you should consider. On the speed dimension, the `frameref` and `subq` options interact with each other fairly strongly. Experience shows that, with one reference frame, `subq=5` (the default setting) takes about 35% more time than `subq=1`. With 6 reference frames, the penalty grows to over 60%. `subq`'s effect on PSNR seems fairly constant regardless of the number of reference frames. Typically, `subq=5` achieves 0.2-0.5 dB higher global PSNR in comparison `subq=1`. This is usually enough to be visible.

  `subq=6` is slower and yields better quality at a reasonable cost. In comparison to `subq=5`, it usually gains 0.1-0.4 dB global PSNR with speed costs varying from 25%-100%. Unlike other levels of `subq`, the behavior of `subq=6` does not depend much on `frameref` and `me`. Instead, the effectiveness of `subq=6` depends mostly upon the number of B-frames used. In normal usage, this means `subq=6` has a large impact on both speed and quality in complex, high motion scenes, but it may not have much effect in low-motion scenes. Note that it is still recommended to always set `bframes` to something other than zero (see below).

  `subq=7` is the slowest, highest quality mode. In comparison to `subq=6`, it usually gains 0.01-0.05 dB global PSNR with speed costs varying from 15%-33%. Since the tradeoff encoding time vs. quality is quite low, you should only use it if you are after every bit saving and if encoding time is not an issue.

- frameref: `frameref` is set to 1 by default, but this should not be taken to imply that it is reasonable to set it to 1. Merely raising `frameref` to 2 gains around 0.15dB PSNR with a 5-10% speed penalty; this seems like a good tradeoff. `frameref=3` gains around 0.25dB PSNR over `frameref=1`, which should be a visible difference. `frameref=3` is around 15% slower than `frameref=1`. Unfortunately, diminishing returns set in rapidly. `frameref=6` can be expected to gain only 0.05-0.1 dB over `frameref=3` at an additional 15% speed penalty. Above `frameref=6`, the quality gains are usually very small (although you should keep in mind throughout this whole discussion that it can vary quite a lot depending on your source). In a fairly typical case, `frameref=12` will improve global PSNR by a tiny 0.02dB over `frameref=6`, at a speed cost of 15%-20%. At such high `frameref` values, the only really good thing that can be said is that increasing it even further will almost certainly never harm PSNR, but the additional quality benefits are barely even measurable, let alone perceptible.

  ##### Note:

  Raising `frameref` to unnecessarily high values can and usually does hurt coding efficiency if you turn CABAC off. With CABAC on (the default behavior), the possibility of setting `frameref` "too high" currently seems too remote to even worry about, and in the future, optimizations may remove the possibility altogether.

  If you care about speed, a reasonable compromise is to use low `subq` and `frameref` values on the first pass, and then raise them on the second pass. Typically, this has a negligible negative effect on the final quality: You will probably lose well under 0.1dB PSNR, which should be much too small of a difference to see. However, different values of `frameref` can occasionally affect frame type decision. Most likely, these are rare outlying cases, but if you want to be pretty sure, consider whether your video has either fullscreen repetitive flashing patterns or very large temporary occlusions which might force an I-frame. Adjust the first-pass `frameref` so it is large enough to contain the duration of the flashing cycle (or occlusion). For example, if the scene flashes back and forth between two images over a duration of three frames, set the first pass `frameref` to 3 or higher. This issue is probably extremely rare in live action video material, but it does sometimes come up in video game captures.

- me: This option is for choosing the motion estimation search method. Altering this option provides a straightforward quality-vs-speed tradeoff. `me=dia` is only a few percent faster than the default search, at a cost of under 0.1dB global PSNR. The default setting (`me=hex`) is a reasonable tradeoff between speed and quality. `me=umh` gains a little under 0.1dB global PSNR, with a speed penalty that varies depending on `frameref`. At high values of `frameref` (e.g. 12 or so), `me=umh` is about 40% slower than the default `me=hex`. With `frameref=3`, the speed penalty incurred drops to 25%-30%.

  `me=esa` uses an exhaustive search that is too slow for practical use.

- partitions=all: This option enables the use of 8x4, 4x8 and 4x4 subpartitions in predicted macroblocks (in addition to the default partitions). Enabling it results in a fairly consistent 10%-15% loss of speed. This option is rather useless in source containing only low motion, however in some high-motion source, particularly source with lots of small moving objects, gains of about 0.1dB can be expected.

- bframes: If you are used to encoding with other codecs, you may have found that B-frames are not always useful. In H.264, this has changed: there are new techniques and block types that are possible in B-frames. Usually, even a naive B-frame choice algorithm can have a significant PSNR benefit. It is interesting to note that using B-frames usually speeds up the second pass somewhat, and may also speed up a single pass encode if adaptive B-frame decision is turned off.

  With adaptive B-frame decision turned off (`x264encopts`'s `nob_adapt`), the optimal value for this setting is usually no more than `bframes=1`, or else high-motion scenes can suffer. With adaptive B-frame decision on (the default behavior), it is safe to use higher values; the encoder will reduce the use of B-frames in scenes where they would hurt compression. The encoder rarely chooses to use more than 3 or 4 B-frames; setting this option any higher will have little effect.

- b_adapt: Note: This is on by default.

  With this option enabled, the encoder will use a reasonably fast decision process to reduce the number of B-frames used in scenes that might not benefit from them as much. You can use `b_bias` to tweak how B-frame-happy the encoder is. The speed penalty of adaptive B-frames is currently rather modest, but so is the potential quality gain. It usually does not hurt, however. Note that this only affects speed and frame type decision on the first pass. `b_adapt` and `b_bias` have no effect on subsequent passes.

- b_pyramid: You might as well enable this option if you are using >=2 B-frames; as the man page says, you get a little quality improvement at no speed cost. Note that these videos cannot be read by libavcodec-based decoders older than about March 5, 2005.

- weight_b: In typical cases, there is not much gain with this option. However, in crossfades or fade-to-black scenes, weighted prediction gives rather large bitrate savings. In MPEG-4 ASP, a fade-to-black is usually best coded as a series of expensive I-frames; using weighted prediction in B-frames makes it possible to turn at least some of these into much smaller B-frames. Encoding time cost is minimal, as no extra decisions need to be made. Also, contrary to what some people seem to guess, the decoder CPU requirements are not much affected by weighted prediction, all else being equal.

  Unfortunately, the current adaptive B-frame decision algorithm has a strong tendency to avoid B-frames during fades. Until this changes, it may be a good idea to add `nob_adapt` to your x264encopts, if you expect fades to have a large effect in your particular video clip.

- threads: This option allows to spawn threads to encode in parallel on multiple CPUs. You can manually select the number of threads to be created or, better, set `threads=auto` and let x264 detect how many CPUs are available and pick an appropriate number of threads. If you have a multi-processor machine, you should really consider using it as it can to increase encoding speed linearly with the number of CPU cores (about 94% per CPU core), with very little quality reduction (about 0.005dB for dual processor, about 0.01dB for a quad processor machine).

#### Options pertaining to miscellaneous preferences

- Two pass encoding: Above, it was suggested to always use two pass encoding, but there are still reasons for not using it. For instance, if you are capturing live TV and encoding in realtime, you are forced to use single-pass. Also, one pass is obviously faster than two passes; if you use the exact same set of options on both passes, two pass encoding is almost twice as slow.

  Still, there are very good reasons for using two pass encoding. For one thing, single pass ratecontrol is not psychic, and it often makes unreasonable choices because it cannot see the big picture. For example, suppose you have a two minute long video consisting of two distinct halves. The first half is a very high-motion scene lasting 60 seconds which, in isolation, requires about 2500kbps in order to look decent. Immediately following it is a much less demanding 60-second scene that looks good at 300kbps. Suppose you ask for 1400kbps on the theory that this is enough to accommodate both scenes. Single pass ratecontrol will make a couple of "mistakes" in such a case. First of all, it will target 1400kbps in both segments. The first segment may end up heavily overquantized, causing it to look unacceptably and unreasonably blocky. The second segment will be heavily underquantized; it may look perfect, but the bitrate cost of that perfection will be completely unreasonable. What is even harder to avoid is the problem at the transition between the two scenes. The first seconds of the low motion half will be hugely over-quantized, because the ratecontrol is still expecting the kind of bitrate requirements it met in the first half of the video. This "error period" of heavily over-quantized low motion will look jarringly bad, and will actually use less than the 300kbps it would have taken to make it look decent. There are ways to mitigate the pitfalls of single-pass encoding, but they may tend to increase bitrate misprediction.

  Multipass ratecontrol can offer huge advantages over a single pass. Using the statistics gathered from the first pass encode, the encoder can estimate, with reasonable accuracy, the "cost" (in bits) of encoding any given frame, at any given quantizer. This allows for a much more rational, better planned allocation of bits between the expensive (high-motion) and cheap (low-motion) scenes. See `qcomp` below for some ideas on how to tweak this allocation to your liking.

  Moreover, two passes need not take twice as long as one pass. You can tweak the options in the first pass for higher speed and lower quality. If you choose your options well, you can get a very fast first pass. The resulting quality in the second pass will be slightly lower because size prediction is less accurate, but the quality difference is normally much too small to be visible. Try, for example, adding `subq=1:frameref=1` to the first pass `x264encopts`. Then, on the second pass, use slower, higher-quality options: `subq=6:frameref=15:partitions=all:me=umh`

- Three pass encoding? x264 offers the ability to make an arbitrary number of consecutive passes. If you specify `pass=1` on the first pass, then use `pass=3` on a subsequent pass, the subsequent pass will both read the statistics from the previous pass, and write its own statistics. An additional pass following this one will have a very good base from which to make highly accurate predictions of frame sizes at a chosen quantizer. In practice, the overall quality gain from this is usually close to zero, and quite possibly a third pass will result in slightly worse global PSNR than the pass before it. In typical usage, three passes help if you get either bad bitrate prediction or bad looking scene transitions when using only two passes. This is somewhat likely to happen on extremely short clips. There are also a few special cases in which three (or more) passes are handy for advanced users, but for brevity, this guide omits discussing those special cases.

- qcomp: `qcomp` trades off the number of bits allocated to "expensive" high-motion versus "cheap" low-motion frames. At one extreme, `qcomp=0` aims for true constant bitrate. Typically this would make high-motion scenes look completely awful, while low-motion scenes would probably look absolutely perfect, but would also use many times more bitrate than they would need in order to look merely excellent. At the other extreme, `qcomp=1` achieves nearly constant quantization parameter (QP). Constant QP does not look bad, but most people think it is more reasonable to shave some bitrate off of the extremely expensive scenes (where the loss of quality is not as noticeable) and reallocate it to the scenes that are easier to encode at excellent quality. `qcomp` is set to 0.6 by default, which may be slightly low for many peoples' taste (0.7-0.8 are also commonly used).

- keyint: `keyint` is solely for trading off file seekability against coding efficiency. By default, `keyint` is set to 250. In 25fps material, this guarantees the ability to seek to within 10 seconds precision. If you think it would be important and useful to be able to seek within 5 seconds of precision, set `keyint=125`; this will hurt quality/bitrate slightly. If you care only about quality and not about seekability, you can set it to much higher values (understanding that there are diminishing returns which may become vanishingly low, or even zero). The video stream will still have seekable points as long as there are some scene changes.

- deblock: This topic is going to be a bit controversial.

  H.264 defines a simple deblocking procedure on I-blocks that uses pre-set strengths and thresholds depending on the QP of the block in question. By default, high QP blocks are filtered heavily, and low QP blocks are not deblocked at all. The pre-set strengths defined by the standard are well-chosen and the odds are very good that they are PSNR-optimal for whatever video you are trying to encode. The `deblock` allow you to specify offsets to the preset deblocking thresholds.

  Many people seem to think it is a good idea to lower the deblocking filter strength by large amounts (say, -3). This is however almost never a good idea, and in most cases, people who are doing this do not understand very well how deblocking works by default.

  The first and most important thing to know about the in-loop deblocking filter is that the default thresholds are almost always PSNR-optimal. In the rare cases that they are not optimal, the ideal offset is plus or minus 1. Adjusting deblocking parameters by a larger amount is almost guaranteed to hurt PSNR. Strengthening the filter will smear more details; weakening the filter will increase the appearance of blockiness.

  It is definitely a bad idea to lower the deblocking thresholds if your source is mainly low in spacial complexity (i.e., not a lot of detail or noise). The in-loop filter does a rather excellent job of concealing the artifacts that occur. If the source is high in spacial complexity, however, artifacts are less noticeable. This is because the ringing tends to look like detail or noise. Human visual perception easily notices when detail is removed, but it does not so easily notice when the noise is wrongly represented. When it comes to subjective quality, noise and detail are somewhat interchangeable. By lowering the deblocking filter strength, you are most likely increasing error by adding ringing artifacts, but the eye does not notice because it confuses the artifacts with detail.

  This still does not justify lowering the deblocking filter strength, however. You can generally get better quality noise from postprocessing. If your H.264 encodes look too blurry or smeared, try playing with `-vf noise` when you play your encoded movie. `-vf noise=8a:4a` should conceal most mild artifacts. It will almost certainly look better than the results you would have gotten just by fiddling with the deblocking filter.

### Encoding setting examples

The following settings are examples of different encoding option combinations that affect the speed vs quality tradeoff at the same target bitrate.

All the encoding settings were tested on a 720x448 @30000/1001 fps video sample, the target bitrate was 900kbps, and the machine was an AMD-64 3400+ at 2400 MHz in 64 bits mode. Each encoding setting features the measured encoding speed (in frames per second) and the PSNR loss (in dB) compared to the "very high quality" setting. Please understand that depending on your source, your machine type and development advancements, you may get very different results.

Description | Encoding options | speed (in fps) | Relative PSNR loss (in dB)
--- | --- | --- | ---
Very high quality | `subq=6:partitions=all:8x8dct:me=umh:frameref=5:bframes=3:b_pyramid=normal:weight_b` | 6fps | 0dB
High quality | `subq=5:8x8dct:frameref=2:bframes=3:b_pyramid=normal:weight_b` | 13fps | -0.89dB
Fast | `subq=4:bframes=2:b_pyramid=normal:weight_b` | 17fps | -1.48dB

## Encoding with the Video For Windows codec family

Video for Windows provides simple encoding by means of binary video codecs. You can encode with the following codecs (if you have more, please tell us!)

Note that support for this is very experimental and some codecs may not work correctly. Some codecs will only work in certain colorspaces, try `-vf format=bgr24` and `-vf format=yuy2` if a codec fails or gives wrong output.

### Video for Windows supported codecs

Video codec file name | Description (FourCC) | md5sum | Comment
--- | --- | --- | ---
aslcodec_vfw.dll | Alparysoft lossless codec vfw (ASLC) | 608af234a6ea4d90cdc7246af5f3f29a |
avimszh.dll | AVImszh (MSZH) | 253118fe1eedea04a95ed6e5f4c28878 | needs `-vf format`
avizlib.dll | AVIzlib (ZLIB) | 2f1cc76bbcf6d77d40d0e23392fa8eda |
divx.dll | DivX4Windows-VFW | acf35b2fc004a89c829531555d73f1e6 |
huffyuv.dll | HuffYUV (lossless) (HFYU) | b74695b50230be4a6ef2c4293a58ac3b |
iccvid.dll | Cinepak Video (cvid) | cb3b7ee47ba7dbb3d23d34e274895133 |
icmw_32.dll | Motion Wavelets (MWV1) | c9618a8fc73ce219ba918e3e09e227f2 |
jp2avi.dll | ImagePower MJPEG2000 (IPJ2) | d860a11766da0d0ea064672c6833768b | `-vf flip`
m3jp2k32.dll | Morgan MJPEG2000 (MJ2C) | f3c174edcbaef7cb947d6357cdfde7ff |
m3jpeg32.dll | Morgan Motion JPEG Codec (MJPEG) | 1cd13fff5960aa2aae43790242c323b1 |
mpg4c32.dll | Microsoft MPEG-4 v1/v2 | b5791ea23f33010d37ab8314681f1256 |
tsccvid.dll | TechSmith Camtasia Screen Codec (TSCC) | 8230d8560c41d444f249802a2700d1d5 | shareware error on windows
vp31vfw.dll | On2 Open Source VP3 Codec (VP31) | 845f3590ea489e2e45e876ab107ee7d2 |
vp4vfw.dll | On2 VP4 Personal Codec (VP40) | fc5480a482ccc594c2898dcc4188b58f |
vp6vfw.dll | On2 VP6 Personal Codec (VP60) | 04d635a364243013898fd09484f913fb |
vp7vfw.dll | On2 VP7 Personal Codec (VP70) | cb4cc3d4ea7c94a35f1d81c3d750bc8d | `-ffourcc VP70`
ViVD2.dll | SoftMedia ViVD V2 codec VfW (GXVE) | a7b4bf5cac630bb9262c3f80d8a773a1 |
msulvc06.DLL | MSU Lossless codec (MSUD) | 294bf9288f2f127bb86f00bfcc9ccdda | Decodable by Window Media Player, not MPlayer (yet).
camcodec.dll | CamStudio lossless video codec (CSCD) | 0efe97ce08bb0e40162ab15ef3b45615 | sf.net/projects/camstudio

The first column contains the codec names that should be passed after the `codec` parameter, like: `-xvfwopts codec=divx.dll` The FourCC code used by each codec is given in the parentheses.

An example to convert an ISO DVD trailer to a VP6 flash video file using compdata bitrate settings:

    mencoder -dvd-device zeiram.iso dvd://7 -o trailer.flv \
    -ovc vfw -xvfwopts codec=vp6vfw.dll:compdata=onepass.mcf -oac mp3lame \
    -lameopts cbr:br=64 -af lavcresample=22050 -vf yadif,scale=320:240,flip \
    -of lavf

### Using vfw2menc to create a codec settings file.

To encode with the Video for Windows codecs, you will need to set bitrate and other options. This is known to work on x86 on both *NIX and Windows.

First you must build the vfw2menc program. It is located in the `TOOLS` subdirectory of the MPlayer source tree. To build on Linux, this can be done using Wine:

    winegcc vfw2menc.c -o vfw2menc -lwinmm -lole32

To build on Windows in MinGW or Cygwin use:

    gcc vfw2menc.c -o vfw2menc.exe -lwinmm -lole32

To build on MSVC you will need getopt. Getopt can be found in the original vfw2menc archive available at: The MPlayer on win32 project.

Below is an example with the VP6 codec.

    vfw2menc -f VP62 -d vp6vfw.dll -s firstpass.mcf

This will open the VP6 codec dialog window. Repeat this step for the second pass and use `-s secondpass.mcf`.

Windows users can use `-xvfwopts codec=vp6vfw.dll:compdata=dialog` to have the codec dialog display before encoding starts.

## Using MEncoder to create QuickTime-compatible files

### Why would one want to produce QuickTime-compatible Files?

There are several reasons why producing QuickTime-compatible files can be desirable.

- You want any computer illiterate to be able to watch your encode on any major platform (Windows, Mac OS X, Unices …).

- QuickTime is able to take advantage of more hardware and software acceleration features of Mac OS X than platform-independent players like MPlayer or VLC. That means that your encodes have a chance to be played smoothly by older G4-powered machines.

- QuickTime 7 supports the next-generation codec H.264, which yields significantly better picture quality than previous codec generations (MPEG-2, MPEG-4 …).

### QuickTime 7 limitations

QuickTime 7 supports H.264 video and AAC audio, but it does not support them muxed in the AVI container format. However, you can use MEncoder to encode the video and audio, and then use an external program such as mp4creator (part of the MPEG4IP suite) to remux the video and audio tracks into an MP4 container.

QuickTime's support for H.264 is limited, so you will need to drop some advanced features. If you encode your video with features that QuickTime 7 does not support, QuickTime-based players will show you a pretty white screen instead of your expected video.

- B-frames: QuickTime 7 supports a maximum of 1 B-frame, i.e. `-x264encopts bframes=1`. This means that `b_pyramid` and `weight_b` will have no effect, since they require `bframes` to be greater than 1.

- Macroblocks: QuickTime 7 does not support 8x8 DCT macroblocks. This option (`8x8dct`) is off by default, so just be sure not to explicitly enable it. This also means that the `i8x8` option will have no effect, since it requires `8x8dct`.

- Aspect ratio: QuickTime 7 does not support SAR (sample aspect ratio) information in MPEG-4 files; it assumes that SAR=1. Read the section on scaling for a workaround.

### Cropping

Suppose you want to rip your freshly bought copy of "The Chronicles of Narnia". Your DVD is region 1, which means it is NTSC. The example below would still apply to PAL, except you would omit `-ofps 24000/1001` and use slightly different `crop` and `scale` dimensions.

After running `mplayer dvd://1`, you follow the process detailed in the section How to deal with telecine and interlacing in NTSC DVDs and discover that it is 24000/1001 fps progressive video. This simplifies the process somewhat, since you do not need to use an inverse telecine filter such as `pullup` or a deinterlacing filter such as `yadif`.

Next, you need to crop out the black bars from the top and bottom of the video, as detailed in this previous section.

### Scaling

The next step is truly heartbreaking. QuickTime 7 does not support MPEG-4 videos with a sample aspect ratio other than 1, so you will need to upscale (which wastes a lot of disk space) or downscale (which loses some details of the source) the video to square pixels. Either way you do it, this is highly inefficient, but simply cannot be avoided if you want your video to be playable by QuickTime 7. MEncoder can apply the appropriate upscaling or downscaling by specifying respectively `-vf scale=-10:-1` or `-vf scale=-1:-10`. This will scale your video to the correct width for the cropped height, rounded to the closest multiple of 16 for optimal compression. Remember that if you are cropping, you should crop first, then scale:

    -vf crop=720:352:0:62,scale=-10:-1

### A/V sync

Because you will be remuxing into a different container, you should always use the `harddup` option to ensure that duplicated frames are actually duplicated in the video output. Without this option, MEncoder will simply put a marker in the video stream that a frame was duplicated, and rely on the client software to show the same frame twice. Unfortunately, this "soft duplication" does not survive remuxing, so the audio would slowly lose sync with the video.

The final filter chain looks like this:

    -vf crop=720:352:0:62,scale=-10:-1,harddup

### Bitrate

As always, the selection of bitrate is a matter of the technical properties of the source, as explained here, as well as a matter of taste. This movie has a fair bit of action and lots of detail, but H.264 video looks good at much lower bitrates than XviD or other MPEG-4 codecs. After much experimentation, the author of this guide chose to encode this movie at 900kbps, and thought that it looked very good. You may decrease bitrate if you need to save more space, or increase it if you need to improve quality.

### Encoding example

You are now ready to encode the video. Since you care about quality, of course you will be doing a two-pass encode. To shave off some encoding time, you can specify the `turbo` option on the first pass; this reduces `subq` and `frameref` to 1. To save some disk space, you can use the `ss` option to strip off the first few seconds of the video. (I found that this particular movie has 32 seconds of credits and logos.) `bframes` can be 0 or 1. The other options are documented in Encoding with the x264 codec and the man page.

    mencoder dvd://1 -o /dev/null -ss 32 -ovc x264 \
    -x264encopts pass=1:turbo:bitrate=900:bframes=1:\
    me=umh:partitions=all:trellis=1:qp_step=4:qcomp=0.7:direct_pred=auto:keyint=300 \
    -vf crop=720:352:0:62,scale=-10:-1,harddup \
    -oac faac -faacopts br=192:mpeg=4:object=2 -channels 2 -srate 48000 \
    -ofps 24000/1001

If you have a multi-processor machine, don't miss the opportunity to dramatically speed-up encoding by enabling x264's multi-threading mode by adding `threads=auto` to your `x264encopts` command-line.

The second pass is the same, except that you specify the output file and set `pass=2`.

    mencoder dvd://1 -o narnia.avi -ss 32 -ovc x264 \
    -x264encopts pass=2:turbo:bitrate=900:frameref=5:bframes=1:\
    me=umh:partitions=all:trellis=1:qp_step=4:qcomp=0.7:direct_pred=auto:keyint=300 \
    -vf crop=720:352:0:62,scale=-10:-1,harddup \
    -oac faac -faacopts br=192:mpeg=4:object=2 -channels 2 -srate 48000 \
    -ofps 24000/1001

The resulting AVI should play perfectly in MPlayer, but of course QuickTime can not play it because it does not support H.264 muxed in AVI. So the next step is to remux the video into an MP4 container.

### Remuxing as MP4

There are several ways to remux AVI files to MP4. You can use mp4creator, which is part of the MPEG4IP suite.

First, demux the AVI into separate audio and video streams using MPlayer.

    mplayer narnia.avi -dumpaudio -dumpfile narnia.aac
    mplayer narnia.avi -dumpvideo -dumpfile narnia.h264

The file names are important; mp4creator requires that AAC audio streams be named .aac and H.264 video streams be named .h264.

Now use mp4creator to create a new MP4 file out of the audio and video streams.

    mp4creator -create=narnia.aac narnia.mp4
    mp4creator -create=narnia.h264 -rate=23.976 narnia.mp4

Unlike the encoding step, you must specify the framerate as a decimal (such as 23.976), not a fraction (such as 24000/1001).

This narnia.mp4 file should now be playable with any QuickTime 7 application, such as QuickTime Player or iTunes. If you are planning to view the video in a web browser with the QuickTime plugin, you should also hint the movie so that the QuickTime plugin can start playing it while it is still downloading. mp4creator can create these hint tracks:

    mp4creator -hint=1 narnia.mp4
    mp4creator -hint=2 narnia.mp4
    mp4creator -optimize narnia.mp4

You can check the final result to ensure that the hint tracks were created successfully:

    mp4creator -list narnia.mp4

You should see a list of tracks: 1 audio, 1 video, and 2 hint tracks.

    Track   Type    Info
    1       audio   MPEG-4 AAC LC, 8548.714 secs, 190 kbps, 48000 Hz
    2       video   H264 Main@5.1, 8549.132 secs, 899 kbps, 848x352 @ 23.976001 fps
    3       hint    Payload mpeg4-generic for track 1
    4       hint    Payload H264 for track 2

### Adding metadata tags

If you want to add tags to your video that show up in iTunes, you can use AtomicParsley.

    AtomicParsley narnia.mp4 --metaEnema --title "The Chronicles of Narnia" --year 2005 --stik Movie --freefree --overWrite

The `--metaEnema` option removes any existing metadata (mp4creator inserts its name in the "encoding tool" tag), and `--freefree` reclaims the space from the deleted metadata. The `--stik` option sets the type of video (such as Movie or TV Show), which iTunes uses to group related video files. The `--overWrite` option overwrites the original file; without it, AtomicParsley creates a new auto-named file in the same directory and leaves the original file untouched.

## Using MEncoder to create VCD/SVCD/DVD-compliant files

### Format Constraints

MEncoder is capable of creating VCD, SCVD and DVD format MPEG files using the libavcodec library. These files can then be used in conjunction with vcdimager or dvdauthor to create discs that will play on a standard set-top player.

The DVD, SVCD, and VCD formats are subject to heavy constraints. Only a small selection of encoded picture sizes and aspect ratios are available. If your movie does not already meet these requirements, you may have to scale, crop or add black borders to the picture to make it compliant.

#### Format Constraints

Format | Resolution | V. Codec | V. Bitrate | Sample Rate | A. Codec | A. Bitrate | FPS | Aspect
--- | --- | --- | --- | --- | --- | --- | --- | ---
NTSC DVD | 720x480, 704x480, 352x480, 352x240 | MPEG-2 | 9800 kbps | 48000 Hz | AC-3,PCM | 1536 kbps (max) | 30000/1001, 24000/1001 | 4:3, 16:9 (only for 720x480)
NTSC DVD | 352x240 These resolutions are rarely used for DVDs because they are fairly low quality. | MPEG-1 | 1856 kbps | 48000 Hz | AC-3,PCM | 1536 kbps (max) | 30000/1001, 24000/1001 | 4:3, 16:9
NTSC SVCD | 480x480 | MPEG-2 | 2600 kbps | 44100 Hz | MP2 | 384 kbps (max) | 30000/1001 | 4:3
NTSC VCD | 352x240 | MPEG-1 | 1150 kbps | 44100 Hz | MP2 | 224 kbps | 24000/1001, 30000/1001 | 4:3
PAL DVD | 720x576, 704x576, 352x576, 352x288 | MPEG-2 | 9800 kbps | 48000 Hz | MP2,AC-3,PCM | 1536 kbps (max) | 25 | 4:3, 16:9 (only for 720x576)
PAL DVD | 352x288 | MPEG-1 | 1856 kbps | 48000 Hz | MP2,AC-3,PCM | 1536 kbps (max) | 25 | 4:3, 16:9
PAL SVCD | 480x576 | MPEG-2 | 2600 kbps | 44100 Hz | MP2 | 384 kbps (max) | 25 | 4:3
PAL VCD | 352x288 | MPEG-1 | 1152 kbps | 44100 Hz | MP2 | 224 kbps | 25 | 4:3

If your movie has 2.35:1 aspect (most recent action movies), you will have to add black borders or crop the movie down to 16:9 to make a DVD or VCD. If you add black borders, try to align them at 16-pixel boundaries in order to minimize the impact on encoding performance. Thankfully DVD has sufficiently excessive bitrate that you do not have to worry too much about encoding efficiency, but SVCD and VCD are highly bitrate-starved and require effort to obtain acceptable quality.

#### GOP Size Constraints

DVD, VCD, and SVCD also constrain you to relatively low GOP (Group of Pictures) sizes. For 30 fps material the largest allowed GOP size is 18. For 25 or 24 fps, the maximum is 15. The GOP size is set using the `keyint` option.

#### Bitrate Constraints

VCD video is required to be CBR at 1152 kbps. This highly limiting constraint also comes along with an extremely low vbv buffer size of 327 kilobits. SVCD allows varying video bitrates up to 2500 kbps, and a somewhat less restrictive vbv buffer size of 917 kilobits is allowed. DVD video bitrates may range anywhere up to 9800 kbps (though typical bitrates are about half that), and the vbv buffer size is 1835 kilobits.

### Output Options

MEncoder has options to control the output format. Using these options we can instruct it to create the correct type of file.

The options for VCD and SVCD are called xvcd and xsvcd, because they are extended formats. They are not strictly compliant, mainly because the output does not contain scan offsets. If you need to generate an SVCD image, you should pass the output file to vcdimager.

VCD:

    -of mpeg -mpegopts format=xvcd

SVCD:

    -of mpeg -mpegopts format=xsvcd

DVD (with timestamps on every frame, if possible):

    -of mpeg -mpegopts format=dvd:tsaf

DVD with NTSC Pullup:

    -of mpeg -mpegopts format=dvd:tsaf:telecine -ofps 24000/1001

This allows 24000/1001 fps progressive content to be encoded at 30000/1001 fps whilst maintaining DVD-compliance.

#### Aspect Ratio

The aspect argument of `-lavcopts` is used to encode the aspect ratio of the file. During playback the aspect ratio is used to restore the video to the correct size.

16:9 or "Widescreen"

    -lavcopts aspect=16/9

4:3 or "Fullscreen"

    -lavcopts aspect=4/3

2.35:1 or "Cinemascope" NTSC

    -vf scale=720:368,expand=720:480 -lavcopts aspect=16/9

To calculate the correct scaling size, use the expanded NTSC width of 854/2.35 = 368

2.35:1 or "Cinemascope" PAL

    -vf scale=720:432,expand=720:576 -lavcopts aspect=16/9

To calculate the correct scaling size, use the expanded PAL width of 1024/2.35 = 432

#### Maintaining A/V sync

In order to maintain audio/video synchronization throughout the encode, MEncoder has to drop or duplicate frames. This works rather well when muxing into an AVI file, but is almost guaranteed to fail to maintain A/V sync with other muxers such as MPEG. This is why it is necessary to append the `harddup` video filter at the end of the filter chain to avoid this kind of problem. You can find more technical information about `harddup` in the section Improving muxing and A/V sync reliability or in the manual page.

#### Sample Rate Conversion

If the audio sample rate in the original file is not the same as required by the target format, sample rate conversion is required. This is achieved using the `-srate` option and the `-af lavcresample` audio filter together.

DVD:

    -srate 48000 -af lavcresample=48000

VCD and SVCD:

    -srate 44100 -af lavcresample=44100

### Using libavcodec for VCD/SVCD/DVD Encoding

#### Introduction

libavcodec can be used to create VCD/SVCD/DVD compliant video by using the appropriate options.

#### lavcopts

This is a list of fields in `-lavcopts` that you may be required to change in order to make a complaint movie for VCD, SVCD, or DVD:

- acodec: `mp2` for VCD, SVCD, or PAL DVD; `ac3` is most commonly used for DVD. PCM audio may also be used for DVD, but this is mostly a big waste of space. Note that MP3 audio is not compliant for any of these formats, but players often have no problem playing it anyway.

- abitrate: 224 for VCD; up to 384 for SVCD; up to 1536 for DVD, but commonly used values range from 192 kbps for stereo to 384 kbps for 5.1 channel sound.

- vcodec: `mpeg1video` for VCD; `mpeg2video` for SVCD; `mpeg2video` is usually used for DVD but you may also use `mpeg1video` for CIF resolutions.

- keyint: Used to set the GOP size. 18 for 30fps material, or 15 for 25/24 fps material. Commercial producers seem to prefer keyframe intervals of 12. It is possible to make this much larger and still retain compatibility with most players. A `keyint` of 25 should never cause any problems.

- vrc_buf_size: 327 for VCD, 917 for SVCD, and 1835 for DVD.

- vrc_minrate: 1152, for VCD. May be left alone for SVCD and DVD.

- vrc_maxrate: 1152 for VCD; 2500 for SVCD; 9800 for DVD. For SVCD and DVD, you might wish to use lower values depending on your own personal preferences and requirements.

- vbitrate: 1152 for VCD; up to 2500 for SVCD; up to 9800 for DVD. For the latter two formats, vbitrate should be set based on personal preference. For instance, if you insist on fitting 20 or so hours on a DVD, you could use vbitrate=400. The resulting video quality would probably be quite bad. If you are trying to squeeze out the maximum possible quality on a DVD, use vbitrate=9800, but be warned that this could constrain you to less than an hour of video on a single-layer DVD.

- vstrict: `vstrict`=0 should be used to create DVDs. Without this option, MEncoder creates a stream that cannot be correctly decoded by some standalone DVD players.

#### Examples

This is a typical minimum set of `-lavcopts` for encoding video:

VCD:

    -lavcopts vcodec=mpeg1video:vrc_buf_size=327:vrc_minrate=1152:\
    vrc_maxrate=1152:vbitrate=1152:keyint=15:acodec=mp2

SVCD:

    -lavcopts vcodec=mpeg2video:vrc_buf_size=917:vrc_maxrate=2500:vbitrate=1800:\
    keyint=15:acodec=mp2

DVD:

    -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=9800:vbitrate=5000:\
    keyint=15:vstrict=0:acodec=ac3

#### Advanced Options

For higher quality encoding, you may also wish to add quality-enhancing options to lavcopts, such as `trell`, `mbd=2`, and others. Note that `qpel` and `v4mv`, while often useful with MPEG-4, are not usable with MPEG-1 or MPEG-2. Also, if you are trying to make a very high quality DVD encode, it may be useful to add `dc=10` to lavcopts. Doing so may help reduce the appearance of blocks in flat-colored areas. Putting it all together, this is an example of a set of lavcopts for a higher quality DVD:

    -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=9800:vbitrate=8000:\
    keyint=15:trell:mbd=2:precmp=2:subcmp=2:cmp=2:dia=-10:predia=-10:cbp:mv0:\
    vqmin=1:lmin=1:dc=10:vstrict=0

### Encoding Audio

VCD and SVCD support MPEG-1 layer II audio, using one of toolame, twolame, or libavcodec's MP2 encoder. The libavcodec MP2 is far from being as good as the other two libraries, however it should always be available to use. VCD only supports constant bitrate audio (CBR) whereas SVCD supports variable bitrate (VBR), too. Be careful when using VBR because some bad standalone players might not support it too well.

For DVD audio, libavcodec's AC-3 codec is used.

#### toolame

For VCD and SVCD:

    -oac toolame -toolameopts br=224

#### twolame

For VCD and SVCD:

    -oac twolame -twolameopts br=224

#### libavcodec

For DVD with 2 channel sound:

    -oac lavc -lavcopts acodec=ac3:abitrate=192

For DVD with 5.1 channel sound:

    -channels 6 -oac lavc -lavcopts acodec=ac3:abitrate=384

For VCD and SVCD:

    -oac lavc -lavcopts acodec=mp2:abitrate=224

### Putting it all Together

This section shows some complete commands for creating VCD/SVCD/DVD compliant videos.

#### PAL DVD

    mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=dvd:tsaf \
      -vf scale=720:576,harddup -srate 48000 -af lavcresample=48000 \
      -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=9800:vbitrate=5000:\
    keyint=15:vstrict=0:acodec=ac3:abitrate=192:aspect=16/9 -ofps 25 \
      -o movie.mpg movie.avi

#### NTSC DVD

    mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=dvd:tsaf \
      -vf scale=720:480,harddup -srate 48000 -af lavcresample=48000 \
      -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=9800:vbitrate=5000:\
    keyint=18:vstrict=0:acodec=ac3:abitrate=192:aspect=16/9 -ofps 30000/1001 \
      -o movie.mpg movie.avi

#### PAL AVI Containing AC-3 Audio to DVD

If the source already has AC-3 audio, use -oac copy instead of re-encoding it.

    mencoder -oac copy -ovc lavc -of mpeg -mpegopts format=dvd:tsaf \
      -vf scale=720:576,harddup -ofps 25 \
      -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=9800:vbitrate=5000:\
    keyint=15:vstrict=0:aspect=16/9 -o movie.mpg movie.avi

#### NTSC AVI Containing AC-3 Audio to DVD

If the source already has AC-3 audio, and is NTSC @ 24000/1001 fps:

    mencoder -oac copy -ovc lavc -of mpeg -mpegopts format=dvd:tsaf:telecine \
      -vf scale=720:480,harddup -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:\
      vrc_maxrate=9800:vbitrate=5000:keyint=15:vstrict=0:aspect=16/9 -ofps 24000/1001 \
      -o movie.mpg movie.avi

#### PAL SVCD

    mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=xsvcd -vf \
        scale=480:576,harddup -srate 44100 -af lavcresample=44100 -lavcopts \
        vcodec=mpeg2video:mbd=2:keyint=15:vrc_buf_size=917:vrc_minrate=600:\
    vbitrate=2500:vrc_maxrate=2500:acodec=mp2:abitrate=224:aspect=16/9 -ofps 25 \
        -o movie.mpg movie.avi

#### NTSC SVCD

    mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=xsvcd  -vf \
        scale=480:480,harddup -srate 44100 -af lavcresample=44100 -lavcopts \
        vcodec=mpeg2video:mbd=2:keyint=18:vrc_buf_size=917:vrc_minrate=600:\
    vbitrate=2500:vrc_maxrate=2500:acodec=mp2:abitrate=224:aspect=16/9 -ofps 30000/1001 \
        -o movie.mpg movie.avi

#### PAL VCD

    mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=xvcd -vf \
        scale=352:288,harddup -srate 44100 -af lavcresample=44100 -lavcopts \
        vcodec=mpeg1video:keyint=15:vrc_buf_size=327:vrc_minrate=1152:\
    vbitrate=1152:vrc_maxrate=1152:acodec=mp2:abitrate=224:aspect=16/9 -ofps 25 \
        -o movie.mpg movie.avi

#### NTSC VCD

    mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=xvcd -vf \
        scale=352:240,harddup -srate 44100 -af lavcresample=44100 -lavcopts \
        vcodec=mpeg1video:keyint=18:vrc_buf_size=327:vrc_minrate=1152:\
    vbitrate=1152:vrc_maxrate=1152:acodec=mp2:abitrate=224:aspect=16/9 -ofps 30000/1001 \
        -o movie.mpg movie.avi