ffmpeg/doc/ffmpeg-doc.texi

\input texinfo @c -*- texinfo -*-

@settitle FFmpeg Documentation
@titlepage
@sp 7
@center @titlefont{FFmpeg Documentation}
@sp 3
@end titlepage


@chapter Introduction

FFmpeg is a very fast video and audio converter. It can also grab from
a live audio/video source.
  
The command line interface is designed to be intuitive, in the sense
that ffmpeg tries to figure out all the parameters, when
possible. You have usually to give only the target bitrate you want.

FFmpeg can also convert from any sample rate to any other, and resize
video on the fly with a high quality polyphase filter.

@chapter Quick Start

@c man begin EXAMPLES
@section Video and Audio grabbing

FFmpeg can use a video4linux compatible video source and any Open Sound
System audio source:

@example
ffmpeg /tmp/out.mpg 
@end example

Note that you must activate the right video source and channel before
launching ffmpeg. You can use any TV viewer such as xawtv
(@url{http://bytesex.org/xawtv/}) by Gerd Knorr which I find very
good. You must also set correctly the audio recording levels with a
standard mixer.

@section Video and Audio file format conversion

* ffmpeg can use any supported file format and protocol as input: 

Examples:

* You can input from YUV files:

@example
ffmpeg -i /tmp/test%d.Y /tmp/out.mpg 
@end example

It will use the files: 
@example
/tmp/test0.Y, /tmp/test0.U, /tmp/test0.V,
/tmp/test1.Y, /tmp/test1.U, /tmp/test1.V, etc...
@end example

The Y files use twice the resolution of the U and V files. They are
raw files, without header. They can be generated by all decent video
decoders. You must specify the size of the image with the @option{-s} option
if ffmpeg cannot guess it.

* You can input from a RAW YUV420P file:

@example
ffmpeg -i /tmp/test.yuv /tmp/out.avi
@end example

The RAW YUV420P is a file containing RAW YUV planar, for each frame first
come the Y plane followed by U and V planes, which are half vertical and
horizontal resolution.

* You can output to a RAW YUV420P file:

@example
ffmpeg -i mydivx.avi -o hugefile.yuv
@end example

* You can set several input files and output files:

@example
ffmpeg -i /tmp/a.wav -s 640x480 -i /tmp/a.yuv /tmp/a.mpg
@end example

Convert the audio file a.wav and the raw yuv video file a.yuv
to mpeg file a.mpg

* You can also do audio and video conversions at the same time:

@example
ffmpeg -i /tmp/a.wav -ar 22050 /tmp/a.mp2
@end example

Convert the sample rate of a.wav to 22050 Hz and encode it to MPEG audio.

* You can encode to several formats at the same time and define a
mapping from input stream to output streams:

@example
ffmpeg -i /tmp/a.wav -ab 64 /tmp/a.mp2 -ab 128 /tmp/b.mp2 -map 0:0 -map 0:0
@end example

Convert a.wav to a.mp2 at 64 kbits and b.mp2 at 128 kbits. '-map
file:index' specify which input stream is used for each output
stream, in the order of the definition of output streams.

* You can transcode decrypted VOBs

@example
ffmpeg -i snatch_1.vob -f avi -vcodec mpeg4 -b 800 -g 300 -bf 2 -acodec mp3 -ab 128 snatch.avi
@end example

This is a typical DVD ripper example, input from a VOB file, output
to an AVI file with MPEG-4 video and MP3 audio, note that in this
command we use B frames so the MPEG-4 stream is DivX5 compatible, GOP
size is 300 that means an INTRA frame every 10 seconds for 29.97 fps
input video.  Also the audio stream is MP3 encoded so you need LAME
support which is enabled using @code{--enable-mp3lame} when
configuring.  The mapping is particularly useful for DVD transcoding
to get the desired audio language.

NOTE: to see the supported input formats, use @code{ffmpeg -formats}.
@c man end

@chapter Invocation

@section Syntax

The generic syntax is:

@example 
@c man begin SYNOPSIS
ffmpeg [[options][@option{-i} @var{input_file}]]... @{[options] @var{output_file}@}...
@c man end
@end example
@c man begin DESCRIPTION
If no input file is given, audio/video grabbing is done.

As a general rule, options are applied to the next specified
file. For example, if you give the @option{-b 64} option, it sets the video
bitrate of the next file. Format option may be needed for raw input
files.

By default, ffmpeg tries to convert as losslessly as possible: it
uses the same audio and video parameter for the outputs as the one
specified for the inputs.
@c man end

@c man begin OPTIONS
@section Main options

@table @option
@item -L
show license

@item -h
show help

@item -formats
show available formats, codecs, protocols, ...

@item -f fmt              
force format

@item -i filename         
input file name

@item -y                  
overwrite output files

@item -t duration         
set the recording time in seconds. @code{hh:mm:ss[.xxx]} syntax is also
supported.

@item -title string       
set the title

@item -author string      
set the author

@item -copyright string   
set the copyright

@item -comment string     
set the comment

@item -hq                 
activate high quality settings

@end table

@section Video Options

@table @option
@item -b bitrate
set the video bitrate in kbit/s (default = 200 kb/s)
@item -r fps           
set frame rate (default = 25)
@item -s size             
set frame size. The format is @samp{WxH} (default 160x128).  The
following abbreviations are recognized:
@table @samp
@item sqcif
128x96
@item qcif
176x144
@item cif
352x288
@item 4cif
704x576
@end table

@item -aspect aspect
set aspect ratio (4:3, 16:9 or 1.3333, 1.7777)
@item -croptop size
set top crop band size (in pixels)
@item -cropbottom size
set bottom crop band size (in pixels)
@item -cropleft size
set left crop band size (in pixels)
@item -cropright size
set right crop band size (in pixels)
@item -vn
disable video recording
@item -bt tolerance       
set video bitrate tolerance (in kbit/s)
@item -maxrate bitrate
set max video bitrate tolerance (in kbit/s)
@item -minrate bitrate
set min video bitrate tolerance (in kbit/s)
@item -bufsize size
set ratecontrol buffere size (in kbit)
@item -vcodec codec       
force video codec to @var{codec}. Use the @code{copy} special value to
tell that the raw codec data must be copied as is.
@item -sameq
use same video quality as source (implies VBR)

@item -pass n  
select the pass number (1 or 2). It is useful to do two pass
encoding. The statistics of the video are recorded in the first pass and
the video at the exact requested bit rate is generated in the second
pass.

@item -passlogfile file   
select two pass log file name to @var{file}.

@end table

@section Advanced Video Options

@table @option
@item -g gop_size         
set the group of picture size
@item -intra              
use only intra frames
@item -qscale q           
use fixed video quantiser scale (VBR)
@item -qmin q             
min video quantiser scale (VBR)
@item -qmax q             
max video quantiser scale (VBR)
@item -qdiff q            
max difference between the quantiser scale (VBR)
@item -qblur blur         
video quantiser scale blur (VBR)
@item -qcomp compression  
video quantiser scale compression (VBR)

@item -rc_init_cplx complexity
initial complexity for 1-pass encoding
@item -b_qfactor factor
qp factor between p and b frames
@item -i_qfactor factor
qp factor between p and i frames
@item -b_qoffset offset
qp offset between p and b frames
@item -i_qoffset offset
qp offset between p and i frames
@item -rc_eq equation
set rate control equation (@pxref{FFmpeg formula
evaluator}). Default is @code{tex^qComp}.
@item -rc_override override
rate control override for specific intervals
@item -me method
set motion estimation method to @var{method}. Available methods are
(from lower to best quality):
@table @samp
@item zero
Try just the (0, 0) vector.
@item phods
@item log
@item x1
@item epzs
(default method)
@item full
exhaustive search (slow and marginally better than epzs)
@end table

@item -dct_algo algo
set dct algorithm to @var{algo}. Available values are:
@table @samp
@item 0
FF_DCT_AUTO (default)
@item 1
FF_DCT_FASTINT
@item 2
FF_DCT_INT
@item 3
FF_DCT_MMX
@item 4
FF_DCT_MLIB
@item 5
FF_DCT_ALTIVEC
@end table

@item -idct_algo algo
set idct algorithm to @var{algo}. Available values are:
@table @samp
@item 0
FF_IDCT_AUTO (default)
@item 1
FF_IDCT_INT          
@item 2
FF_IDCT_SIMPLE       
@item 3
FF_IDCT_SIMPLEMMX    
@item 4
FF_IDCT_LIBMPEG2MMX  
@item 5
FF_IDCT_PS2          
@item 6
FF_IDCT_MLIB         
@item 7
FF_IDCT_ARM          
@item 8
FF_IDCT_ALTIVEC      
@item 9
FF_IDCT_SH4          
@item 10
FF_IDCT_SIMPLEARM    
@end table

@item -er n
set error resilience to @var{n}.
@table @samp
@item 1 
FF_ER_CAREFULL (default)
@item 2
FF_ER_COMPLIANT
@item 3
FF_ER_AGGRESSIVE
@item 4
FF_ER_VERY_AGGRESSIVE
@end table

@item -ec bit_mask
set error concealment to @var{bit_mask}. @var{bit_mask} is a bit mask of
the following values:
@table @samp
@item 1
FF_EC_GUESS_MVS (default=enabled)
@item 2
FF_EC_DEBLOCK (default=enabled)
@end table

@item -bf frames
use 'frames' B frames (supported for MPEG-1, MPEG-2 and MPEG-4)
@item -mbd mode
macroblock decision
@table @samp
@item 0
FF_MB_DECISION_SIMPLE: use mb_cmp (cannot change it yet in ffmpeg)
@item 1
FF_MB_DECISION_BITS: chooses the one which needs the fewest bits
@item 2
FF_MB_DECISION_RD: rate distoration
@end table

@item -4mv
use four motion vector by macroblock (only MPEG-4)
@item -part
use data partitioning (only MPEG-4)
@item -bug param
workaround not auto detected encoder bugs
@item -strict strictness
how strictly to follow the standarts
@item -aic
enable Advanced intra coding (h263+)
@item -umv
enable Unlimited Motion Vector (h263+)

@item -deinterlace
deinterlace pictures
@item -psnr
calculate PSNR of compressed frames
@item -vstats
dump video coding statistics to @file{vstats_HHMMSS.log}.
@item -vhook module
insert video processing @var{module}. @var{module} contains the module
name and its parameters separated by spaces.
@end table

@section Audio Options

@table @option
@item -ab bitrate         
set audio bitrate (in kbit/s)
@item -ar freq    
set the audio sampling freq (default = 44100 Hz)
@item -ab bitrate 
set the audio bitrate in kbit/s (default = 64)
@item -ac channels
set the number of audio channels (default = 1)
@item -an
disable audio recording
@item -acodec codec
force audio codec to @var{codec}. Use the @code{copy} special value to
tell that the raw codec data must be copied as is.
@end table

@section Audio/Video grab options

@table @option
@item -vd device
set video grab device (e.g. @file{/dev/video0})
@item -vc channel
set video grab channel (DV1394 only)
@item -tvstd standard
set television standard (NTSC, PAL (SECAM))
@item -dv1394
set DV1394 grab
@item -ad device
set audio device (e.g. @file{/dev/dsp})
@end table

@section Advanced options

@table @option
@item -map file:stream    
set input stream mapping
@item -debug
print specific debug info
@item -benchmark          
add timings for benchmarking
@item -hex                
dump each input packet
@item -bitexact
only use bit exact algorithms (for codec testing)
@item -ps size
set packet size in bits
@item -re
read input at native frame rate. Mainly used to simulate a grab device.
@item -loop
loop over the input stream. Currently it works only for image
streams. This option is used for ffserver automatic testing.
@end table

@node FFmpeg formula evaluator
@section FFmpeg formula evaluator

When evaluating a rate control string, FFmpeg uses an internal formula
evaluator. 

The following binary operators are available: @code{+}, @code{-},
@code{*}, @code{/}, @code{^}.

The following unary operators are available: @code{+}, @code{-},
@code{(...)}.

The following functions are available:
@table @var
@item sinh(x)
@item cosh(x)
@item tanh(x)
@item sin(x)
@item cos(x)
@item tan(x)
@item exp(x)
@item log(x)
@item squish(x)
@item gauss(x)
@item abs(x)
@item max(x, y)
@item min(x, y)
@item gt(x, y)
@item lt(x, y)
@item eq(x, y)
@item bits2qp(bits)
@item qp2bits(qp)
@end table

The following constants are available:
@table @var
@item PI
@item E
@item iTex
@item pTex
@item tex
@item mv
@item fCode
@item iCount
@item mcVar
@item var
@item isI
@item isP
@item isB
@item avgQP
@item qComp
@item avgIITex
@item avgPITex
@item avgPPTex
@item avgBPTex
@item avgTex
@end table

@c man end

@ignore

@setfilename ffmpeg
@settitle FFmpeg video converter

@c man begin SEEALSO
ffserver(1), ffplay(1) and the html documentation of @file{ffmpeg}.
@c man end

@c man begin AUTHOR
Fabrice Bellard
@c man end

@end ignore

@section Protocols

The filename can be @file{-} to read from the standard input or to write
to the standard output.

ffmpeg handles also many protocols specified with the URL syntax.

Use 'ffmpeg -formats' to have a list of the supported protocols.

The protocol @code{http:} is currently used only to communicate with
ffserver (see the ffserver documentation). When ffmpeg will be a
video player it will also be used for streaming :-)

@chapter Tips

@itemize
@item For streaming at very low bit rate application, use a low frame rate
and a small gop size. This is especially true for real video where
the Linux player does not seem to be very fast, so it can miss
frames. An example is:

@example
ffmpeg -g 3 -r 3 -t 10 -b 50 -s qcif -f rv10 /tmp/b.rm
@end example

@item  The parameter 'q' which is displayed while encoding is the current
quantizer. The value of 1 indicates that a very good quality could
be achieved. The value of 31 indicates the worst quality. If q=31
too often, it means that the encoder cannot compress enough to meet
your bit rate. You must either increase the bit rate, decrease the
frame rate or decrease the frame size.

@item If your computer is not fast enough, you can speed up the
compression at the expense of the compression ratio. You can use
'-me zero' to speed up motion estimation, and '-intra' to disable
completely motion estimation (you have only I frames, which means it
is about as good as JPEG compression).

@item To have very low bitrates in audio, reduce the sampling frequency
(down to 22050 kHz for mpeg audio, 22050 or 11025 for ac3).

@item To have a constant quality (but a variable bitrate), use the option
'-qscale n' when 'n' is between 1 (excellent quality) and 31 (worst
quality).

@item When converting video files, you can use the '-sameq' option which
uses in the encoder the same quality factor than in the decoder. It
allows to be almost lossless in encoding.

@end itemize

@chapter Supported File Formats and Codecs

You can use the @code{-formats} option to have an exhaustive list.

@section File Formats

FFmpeg supports the following file formats through the @code{libavformat}
library:

@multitable @columnfractions .4 .1 .1
@item Supported File Format @tab Encoding @tab Decoding @tab Comments
@item MPEG audio @tab X @tab X
@item MPEG1 systems @tab X  @tab  X 
@tab muxed audio and video
@item MPEG2 PS @tab X  @tab  X 
@tab also known as @code{VOB} file
@item MPEG2 TS @tab    @tab  X 
@tab also known as DVB Transport Stream
@item ASF@tab X @tab X 
@item AVI@tab X @tab X 
@item WAV@tab X @tab X 
@item Macromedia Flash@tab X @tab X
@tab Only embedded audio is decoded
@item FLV              @tab  X @tab X
@tab Macromedia Flash video files
@item Real Audio and Video @tab X @tab X 
@item Raw AC3 @tab X  @tab  X 
@item Raw MJPEG @tab X  @tab  X 
@item Raw MPEG video @tab X  @tab  X 
@item Raw PCM8/16 bits, mulaw/Alaw@tab X  @tab  X 
@item SUN AU format @tab X  @tab  X 
@item Quicktime        @tab X @tab  X 
@item MPEG4            @tab X @tab  X 
@tab MPEG4 is a variant of Quicktime
@item Raw MPEG4 video  @tab  X @tab  X 
@item DV               @tab  @tab X
@item 4xm              @tab    @tab X
@tab 4X Technologies format, used in some games
@item Playstation STR  @tab    @tab X
@item Id RoQ           @tab    @tab X
@tab used in Quake III, Jedi Knight 2, other computer games
@item Interplay MVE    @tab    @tab X
@tab format used in various Interplay computer games
@item WC3 Movie        @tab    @tab X
@tab multimedia format used in Origin's Wing Commander III computer game
@end multitable

@code{X} means that the encoding (resp. decoding) is supported.

@section Image Formats

FFmpeg can read and write images for each frame of a video sequence. The
following image formats are supported:

@multitable @columnfractions .4 .1 .1
@item Supported Image Format @tab Encoding @tab Decoding @tab Comments
@item PGM, PPM     @tab X @tab X 
@item PAM          @tab X @tab X @tab PAM is a PNM extension with alpha support
@item PGMYUV       @tab X @tab X @tab PGM with U and V components in YUV 4:2:0
@item JPEG         @tab X @tab X @tab Progressive JPEG is not supported
@item .Y.U.V       @tab X @tab X @tab One raw file per component
@item Animated GIF @tab X @tab X @tab Only uncompressed GIFs are generated
@item PNG          @tab X @tab X @tab 2 bit and 4 bit/pixel not supported yet
@end multitable

@code{X} means that the encoding (resp. decoding) is supported.

@section Video Codecs

@multitable @columnfractions .4 .1 .1 .7
@item Supported Codec @tab Encoding @tab Decoding @tab Comments
@item MPEG1 video            @tab  X  @tab  X
@item MPEG2 video            @tab  X  @tab  X 
@item MPEG4                  @tab  X  @tab  X @tab Also known as DIVX4/5
@item MSMPEG4 V1             @tab  X  @tab  X
@item MSMPEG4 V2             @tab  X  @tab  X
@item MSMPEG4 V3             @tab  X  @tab  X @tab Also known as DIVX3
@item WMV7                   @tab  X  @tab  X
@item WMV8                   @tab  X  @tab  X @tab Not completely working
@item H263(+)                @tab  X  @tab  X @tab Also known as Real Video 1.0
@item MJPEG                  @tab  X  @tab  X 
@item DV                     @tab     @tab  X 
@item Huff YUV               @tab  X  @tab  X
@item Asus v1                @tab  X  @tab  X @tab fourcc: ASV1
@item Asus v2                @tab  X  @tab  X @tab fourcc: ASV2
@item Creative YUV           @tab     @tab  X @tab fourcc: CYUV
@item H.264                  @tab     @tab  X
@item Sorenson Video 1       @tab     @tab  X @tab fourcc: SVQ1
@item Sorenson Video 3       @tab     @tab  X @tab fourcc: SVQ3
@item On2 VP3                @tab     @tab  X @tab still experimental
@item Intel Indeo 3          @tab     @tab  X @tab only works on i386 right now
@item FLV                    @tab  X  @tab  X @tab Flash H263 variant
@item ATI VCR1               @tab     @tab  X @tab fourcc: VCR1
@item Cirrus Logic AccuPak   @tab     @tab  X @tab fourcc: CLJR
@item 4X Video               @tab     @tab  X @tab used in certain computer games
@item Sony Playstation MDEC  @tab     @tab  X 
@item Id RoQ                 @tab     @tab  X @tab used in Quake III, Jedi Knight 2, other computer games
@item Xan/WC3                @tab     @tab  X @tab used in Wing Commander III .MVE files
@end multitable

@code{X} means that the encoding (resp. decoding) is supported.

Check at @url{http://www.mplayerhq.hu/~michael/codec-features.html} to
get a precise comparison of FFmpeg MPEG4 codec compared to the other
solutions.

@section Audio Codecs

@multitable @columnfractions .4 .1 .1 .1 .7
@item Supported Codec @tab Encoding @tab Decoding @tab Comments
@item MPEG audio layer 2     @tab  IX  @tab  IX 
@item MPEG audio layer 1/3   @tab IX   @tab  IX
@tab MP3 encoding is supported through the external library LAME
@item AC3                    @tab  IX  @tab  X
@tab liba52 is used internally for decoding
@item Vorbis                 @tab  X   @tab  X
@tab supported through the external library libvorbis
@item WMA V1/V2              @tab      @tab X
@item Microsoft ADPCM        @tab X    @tab X
@item MS IMA ADPCM           @tab X    @tab X
@item QT IMA ADPCM           @tab      @tab X
@item 4X IMA ADPCM           @tab      @tab X
@item Duck DK3 IMA ADPCM     @tab      @tab X
@tab used in some Sega Saturn console games
@item Duck DK4 IMA ADPCM     @tab      @tab X
@tab used in some Sega Saturn console games
@item RA144                  @tab      @tab X
@tab Real 14400 bit/s codec
@item RA288                  @tab      @tab X
@tab Real 28800 bit/s codec
@item AMR-NB                 @tab X    @tab X
@tab supported through an external library
@item DV audio               @tab      @tab X
@item Id RoQ DPCM            @tab      @tab X
@tab used in Quake III, Jedi Knight 2, other computer games
@item Interplay MVE DPCM     @tab      @tab X
@tab used in various Interplay computer games
@item Xan DPCM               @tab      @tab X
@tab used in Origin's Wing Commander IV AVI files
@end multitable

@code{X} means that the encoding (resp. decoding) is supported.

@code{I} means that an integer only version is available too (ensures highest
performances on systems without hardware floating point support).

@chapter Platform Specific information

@section Linux

ffmpeg should be compiled with at least GCC 2.95.3. GCC 3.2 is the
preferred compiler now for ffmpeg. All future optimizations will depend on
features only found in GCC 3.2.

@section BSD

@section Windows

@subsection Native Windows compilation

@itemize
@item Install the current versions of MSYS and MinGW from
@url{http://www.mingw.org/}. You can find detailed installation
instructions in the download section and the FAQ.

@item If you want to test the FFmpeg Simple Media Player, also download 
the MinGW development library of SDL 1.2.x
(@file{SDL-devel-1.2.x-mingw32.tar.gz}) from
@url{http://www.libsdl.org}. Unpack it in a temporary place, and
unpack the archive @file{i386-mingw32msvc.tar.gz} in the MinGW tool
directory.

@item Extract the current version of FFmpeg (the latest release version or the current CVS snapshot whichever is recommended).
 
@item Start the MSYS shell (file @file{msys.bat}).

@item Change to the FFMPEG directory and follow
 the instructions of how to compile ffmpeg (file
@file{INSTALL}). Usually, launching @file{./configure} and @file{make}
suffices. If you have problems using SDL, verify that
@file{sdl-config} can be launched from the MSYS command line.

@item You can install FFmpeg in @file{Program Files/FFmpeg} by typing @file{make install}.

@end itemize

Note: The target @file{make wininstaller} can be used to create a Nullsoft based Windows installer for FFmpeg and FFplay.

@subsection How to create a single Windows DLL from libavcodec and libavformat
 
Read @url{http://ffmpeg.org/win32.html}.

@subsection Cross compilation for Windows with Linux

You must use the MinGW cross compilation tools available at
@url{http://www.mingw.org/}.

Then configure ffmpeg with the following options:
@example
./configure --enable-mingw32 --cross-prefix=i386-mingw32msvc-
@end example
(you can change the cross-prefix according to the prefix choosen for the
MinGW tools).

Then you can easily test ffmpeg with wine
(@url{http://www.winehq.com/}).

@section MacOS X

@section BeOS

The configure script should guess the configuration itself.
Networking support is currently not finished.
errno issues fixed by Andrew Bachmann.

Old stuff:

Fran<EFBFBD>ois Revol - revol at free dot fr - April 2002

The configure script should guess the configuration itself, 
however I still didn't tested building on net_server version of BeOS.

ffserver is broken (needs poll() implementation).

There is still issues with errno codes, which are negative in BeOs, and
that ffmpeg negates when returning. This ends up turning errors into 
valid results, then crashes.
(To be fixed)

@chapter Developers Guide

@section API
@itemize
@item libavcodec is the library containing the codecs (both encoding and
  decoding). See @file{libavcodec/apiexample.c} to see how to use it.

@item libavformat is the library containing the file formats handling (mux and
  demux code for several formats). See @file{ffplay.c} to use it in a
player. See @file{output_example.c} to use it to generate audio or video
streams.

@end itemize

@section Integrating libavcodec or libavformat in your program

You can integrate all the source code of the libraries to link them
statically to avoid any version problem. All you need is to provide a
'config.mak' and a 'config.h' in the parent directory. See the defines
generated by ./configure to understand what is needed.

You can use libavcodec or libavformat in your commercial program, but
@emph{any patch you make must be published}. The best way to proceed is
to send your patches to the ffmpeg mailing list.

@section Coding Rules

ffmpeg is programmed in ANSI C language. GCC extensions are
tolerated. Indent size is 4. The TAB character should not be used.

The presentation is the one specified by 'indent -i4 -kr'.

Main priority in ffmpeg is simplicity and small code size (=less
bugs).

Comments: for functions visible from other modules, use the JavaDoc
format (see examples in @file{libav/utils.c}) so that a documentation
can be generated automatically.

@section Submitting patches

When you submit your patch, try to send a unified diff (diff '-u'
option). I cannot read other diffs :-)

Run the regression tests before submitting a patch so that you can
verify that there are no big problems.

Patches should be posted as base64 encoded attachments (or any other
encoding which ensures that the patch wont be trashed during 
transmission) to the ffmpeg-devel mailinglist, see 
@url{http://lists.sourceforge.net/lists/listinfo/ffmpeg-devel}

@section Regression tests

Before submitting a patch (or committing with CVS), you should at least
test that you did not break anything.

The regression test build a synthetic video stream and a synthetic
audio stream. Then these are encoded then decoded with all codecs or
formats. The CRC (or MD5) of each generated file is recorded in a
result file. Then a 'diff' is launched with the reference results and
the result file.

The regression test then goes on to test the ffserver code with a 
limited set of streams. It is important that this step runs correctly
as well.

Run 'make test' to test all the codecs.

Run 'make fulltest' to test all the codecs, formats and ffserver.

[Of course, some patches may change the regression tests results. In
this case, the regression tests reference results shall be modified
accordingly].

@bye