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FFmpeg
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<TITLE>FFmpeg Documentation</TITLE>
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<H1>FFmpeg Documentation</H1>
<P>
<P><HR><P>
<H1>Table of Contents</H1>
<UL>
<LI><A NAME="TOC1" HREF="ffmpeg-doc.html#SEC1">1. Introduction</A>
<LI><A NAME="TOC2" HREF="ffmpeg-doc.html#SEC2">2. Quick Start</A>
<UL>
<LI><A NAME="TOC3" HREF="ffmpeg-doc.html#SEC3">2.1 Video and Audio grabbing</A>
<LI><A NAME="TOC4" HREF="ffmpeg-doc.html#SEC4">2.2 Video and Audio file format convertion</A>
</UL>
<LI><A NAME="TOC5" HREF="ffmpeg-doc.html#SEC5">3. Invocation</A>
<UL>
<LI><A NAME="TOC6" HREF="ffmpeg-doc.html#SEC6">3.1 Syntax</A>
<LI><A NAME="TOC7" HREF="ffmpeg-doc.html#SEC7">3.2 Main options</A>
<LI><A NAME="TOC8" HREF="ffmpeg-doc.html#SEC8">3.3 Video Options</A>
<LI><A NAME="TOC9" HREF="ffmpeg-doc.html#SEC9">3.4 Audio Options</A>
<LI><A NAME="TOC10" HREF="ffmpeg-doc.html#SEC10">3.5 Advanced options</A>
<LI><A NAME="TOC11" HREF="ffmpeg-doc.html#SEC11">3.6 Protocols</A>
</UL>
<LI><A NAME="TOC12" HREF="ffmpeg-doc.html#SEC12">4. Tips</A>
<LI><A NAME="TOC13" HREF="ffmpeg-doc.html#SEC13">5. Supported File Formats and Codecs</A>
<UL>
<LI><A NAME="TOC14" HREF="ffmpeg-doc.html#SEC14">5.1 File Formats</A>
<LI><A NAME="TOC15" HREF="ffmpeg-doc.html#SEC15">5.2 Video Codecs</A>
<LI><A NAME="TOC16" HREF="ffmpeg-doc.html#SEC16">5.3 Audio Codecs</A>
</UL>
<LI><A NAME="TOC17" HREF="ffmpeg-doc.html#SEC17">6. Platform Specific information</A>
<UL>
<LI><A NAME="TOC18" HREF="ffmpeg-doc.html#SEC18">6.1 Linux</A>
<LI><A NAME="TOC19" HREF="ffmpeg-doc.html#SEC19">6.2 BSD</A>
<LI><A NAME="TOC20" HREF="ffmpeg-doc.html#SEC20">6.3 Windows</A>
<LI><A NAME="TOC21" HREF="ffmpeg-doc.html#SEC21">6.4 MacOS X</A>
<LI><A NAME="TOC22" HREF="ffmpeg-doc.html#SEC22">6.5 BeOS</A>
</UL>
<LI><A NAME="TOC23" HREF="ffmpeg-doc.html#SEC23">7. Developpers Guide</A>
<UL>
<LI><A NAME="TOC24" HREF="ffmpeg-doc.html#SEC24">7.1 API</A>
<LI><A NAME="TOC25" HREF="ffmpeg-doc.html#SEC25">7.2 Integrating libavcodec or libavformat in your program</A>
<LI><A NAME="TOC26" HREF="ffmpeg-doc.html#SEC26">7.3 Coding Rules</A>
<LI><A NAME="TOC27" HREF="ffmpeg-doc.html#SEC27">7.4 Submitting patches</A>
<LI><A NAME="TOC28" HREF="ffmpeg-doc.html#SEC28">7.5 Regression tests</A>
</UL>
</UL>
<P><HR><P>

<P>
FFmpeg Documentation


<H1><A NAME="SEC1" HREF="ffmpeg-doc.html#TOC1">1. Introduction</A></H1>

<P>
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.


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


<H1><A NAME="SEC2" HREF="ffmpeg-doc.html#TOC2">2. Quick Start</A></H1>


<H2><A NAME="SEC3" HREF="ffmpeg-doc.html#TOC3">2.1 Video and Audio grabbing</A></H2>

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

<PRE>
  ffmpeg /tmp/out.mpg 
</PRE>

<P>
  Note that you must activate the right video source and channel
  before launching ffmpeg. You can use any TV viewer such as xawtv by
  Gerd Knorr which I find very good. You must also set correctly the
  audio recording levels with a standard mixer.


<H2><A NAME="SEC4" HREF="ffmpeg-doc.html#TOC4">2.2 Video and Audio file format convertion</A></H2>

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


<P>
Examples:


<P>
* You can input from YUV files:


<PRE>
  ffmpeg -i /tmp/test%d.Y /tmp/out.mpg 
</PRE>

<P>
  It will use the files: 

<PRE>
       /tmp/test0.Y, /tmp/test0.U, /tmp/test0.V,
       /tmp/test1.Y, /tmp/test1.U, /tmp/test1.V, etc...
</PRE>

<P>
  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 '-s' option
  if ffmpeg cannot guess it.


<P>
* You can input from a RAW YUV420P file:


<PRE>
  ffmpeg -i /tmp/test.yuv /tmp/out.avi
</PRE>

<P>
  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.


<P>
* You can output to a RAW YUV420P file:


<PRE>
  ffmpeg -i mydivx.avi -o hugefile.yuv
</PRE>

<P>
* You can set several input files and output files:


<PRE>
  ffmpeg -i /tmp/a.wav -s 640x480 -i /tmp/a.yuv /tmp/a.mpg
</PRE>

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


<P>
* You can also do audio and video convertions at the same time:


<PRE>
  ffmpeg -i /tmp/a.wav -ar 22050 /tmp/a.mp2
</PRE>

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


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


<PRE>
  ffmpeg -i /tmp/a.wav -ab 64 /tmp/a.mp2 -ab 128 /tmp/b.mp2 -map 0:0 -map 0:0
</PRE>

<P>
  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.


<P>
* You can transcode decrypted VOBs


<PRE>
  ffmpeg -i snatch_1.vob -f avi -vcodec mpeg4 -b 800 -g 300 -bf 2 -acodec mp3 -ab 128 snatch.avi
</PRE>

<P>
  This is a typicall 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</CODE> when
  configuring.  The mapping is particullary usefull for DVD transcoding
  to get the desired audio language.


<P>
  NOTE: to see the supported input formats, use <CODE>ffmpeg -formats</CODE>.


<H1><A NAME="SEC5" HREF="ffmpeg-doc.html#TOC5">3. Invocation</A></H1>


<H2><A NAME="SEC6" HREF="ffmpeg-doc.html#TOC6">3.1 Syntax</A></H2>

<P>
 The generic syntax is:


<PRE>
  ffmpeg [[options][-i input_file]]... {[options] output_file}...
</PRE>

<P>
  If no input file is given, audio/video grabbing is done.


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


<P>
  By default, ffmpeg tries to convert as losslessly as possible: it
  uses the same audio and video parameter fors the outputs as the one
  specified for the inputs.


<H2><A NAME="SEC7" HREF="ffmpeg-doc.html#TOC7">3.2 Main options</A></H2>

<DL COMPACT>

<DT><SAMP>`-L'</SAMP>
<DD>
show license
<DT><SAMP>`-h'</SAMP>
<DD>
                  show help
<DT><SAMP>`-formats'</SAMP>
<DD>
show available formats, codecs, protocols, ...
<DT><SAMP>`-f fmt'</SAMP>
<DD>
force format
<DT><SAMP>`-i filename'</SAMP>
<DD>
input file name

<DT><SAMP>`-y'</SAMP>
<DD>
overwrite output files

<DT><SAMP>`-t duration'</SAMP>
<DD>
set the recording time in seconds. <CODE>hh:mm:ss[.xxx]</CODE> syntax is also
supported.

<DT><SAMP>`-title string'</SAMP>
<DD>
set the title

<DT><SAMP>`-author string'</SAMP>
<DD>
set the author

<DT><SAMP>`-copyright string'</SAMP>
<DD>
set the copyright

<DT><SAMP>`-comment string'</SAMP>
<DD>
set the comment

<DT><SAMP>`-b bitrate'</SAMP>
<DD>
set video bitrate (in kbit/s)
</DL>


<H2><A NAME="SEC8" HREF="ffmpeg-doc.html#TOC8">3.3 Video Options</A></H2>

<DL COMPACT>

<DT><SAMP>`-s size'</SAMP>
<DD>
set frame size                       [160x128]
<DT><SAMP>`-r fps'</SAMP>
<DD>
set frame rate                       [25]
<DT><SAMP>`-b bitrate'</SAMP>
<DD>
set the video bitrate in kbit/s      [200]
<DT><SAMP>`-vn'</SAMP>
<DD>
disable video recording              [no]
<DT><SAMP>`-bt tolerance'</SAMP>
<DD>
set video bitrate tolerance (in kbit/s)
<DT><SAMP>`-sameq'</SAMP>
<DD>
use same video quality as source (implies VBR)

<DT><SAMP>`-pass n'</SAMP>
<DD>
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.

<DT><SAMP>`-passlogfile file'</SAMP>
<DD>
select two pass log file name

</DL>


<H2><A NAME="SEC9" HREF="ffmpeg-doc.html#TOC9">3.4 Audio Options</A></H2>

<DL COMPACT>

<DT><SAMP>`-ab bitrate'</SAMP>
<DD>
set audio bitrate (in kbit/s)
<DT><SAMP>`-ar freq'</SAMP>
<DD>
 set the audio sampling freq          [44100]
<DT><SAMP>`-ab bitrate'</SAMP>
<DD>
 set the audio bitrate in kbit/s      [64]
<DT><SAMP>`-ac channels'</SAMP>
<DD>
 set the number of audio channels     [1]
<DT><SAMP>`-an'</SAMP>
<DD>
 disable audio recording              [no]
</DL>


<H2><A NAME="SEC10" HREF="ffmpeg-doc.html#TOC10">3.5 Advanced options</A></H2>

<DL COMPACT>

<DT><SAMP>`-map file:stream'</SAMP>
<DD>
set input stream mapping
<DT><SAMP>`-g gop_size'</SAMP>
<DD>
set the group of picture size
<DT><SAMP>`-intra'</SAMP>
<DD>
use only intra frames
<DT><SAMP>`-qscale q'</SAMP>
<DD>
use fixed video quantiser scale (VBR)
<DT><SAMP>`-qmin q'</SAMP>
<DD>
min video quantiser scale (VBR)
<DT><SAMP>`-qmax q'</SAMP>
<DD>
max video quantiser scale (VBR)
<DT><SAMP>`-qdiff q'</SAMP>
<DD>
max difference between the quantiser scale (VBR)
<DT><SAMP>`-qblur blur'</SAMP>
<DD>
video quantiser scale blur (VBR)
<DT><SAMP>`-qcomp compression'</SAMP>
<DD>
video quantiser scale compression (VBR)
<DT><SAMP>`-vd device'</SAMP>
<DD>
set video device
<DT><SAMP>`-vcodec codec'</SAMP>
<DD>
force video codec
<DT><SAMP>`-me method'</SAMP>
<DD>
set motion estimation method
<DT><SAMP>`-bf frames'</SAMP>
<DD>
use 'frames' B frames (only MPEG-4)
<DT><SAMP>`-hq'</SAMP>
<DD>
activate high quality settings
<DT><SAMP>`-4mv'</SAMP>
<DD>
use four motion vector by macroblock (only MPEG-4)
<DT><SAMP>`-ad device'</SAMP>
<DD>
set audio device
<DT><SAMP>`-acodec codec'</SAMP>
<DD>
force audio codec
<DT><SAMP>`-deinterlace'</SAMP>
<DD>
deinterlace pictures
<DT><SAMP>`-benchmark'</SAMP>
<DD>
add timings for benchmarking
<DT><SAMP>`-hex'</SAMP>
<DD>
dump each input packet
<DT><SAMP>`-psnr'</SAMP>
<DD>
calculate PSNR of compressed frames
<DT><SAMP>`-vstats'</SAMP>
<DD>
dump video coding statistics to file
</DL>


<H2><A NAME="SEC11" HREF="ffmpeg-doc.html#TOC11">3.6 Protocols</A></H2>

<P>
The filename can be <TT>`-'</TT> to read from the standard input or to write
to the standard output.


<P>
ffmpeg handles also many protocols specified with the URL syntax.


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


<P>
 The protocol <CODE>http:</CODE> 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 :-)


<H1><A NAME="SEC12" HREF="ffmpeg-doc.html#TOC12">4. Tips</A></H1>


<UL>
<LI>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:


<PRE>
  ffmpeg -g 3 -r 3 -t 10 -b 50 -s qcif -f rv10 /tmp/b.rm
</PRE>

<LI>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.

<LI>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
  completly motion estimation (you have only I frames, which means it
  is about as good as JPEG compression).

<LI>To have very low bitrates in audio, reduce the sampling frequency

  (down to 22050 kHz for mpeg audio, 22050 or 11025 for ac3).

<LI>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).

<LI>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.

</UL>


<H1><A NAME="SEC13" HREF="ffmpeg-doc.html#TOC13">5. Supported File Formats and Codecs</A></H1>

<P>
You can use the <CODE>-formats</CODE> option to have an exhaustive list.


<H2><A NAME="SEC14" HREF="ffmpeg-doc.html#TOC14">5.1 File Formats</A></H2>

<P>
FFmpeg supports the following file formats thru the <CODE>libavformat</CODE>
library.


<TABLE BORDER>

<TR><TD>Supported File Format </TD><TD> Encoding </TD><TD> Decoding </TD><TD> Comments</TD>

</TR>
<TR><TD>MPEG audio </TD><TD> X </TD><TD> X</TD>

</TR>
<TR><TD>MPEG1 systems </TD><TD> X  </TD><TD>  X</TD>

</TD><TD> muxed audio and video
</TR>
<TR><TD>MPEG2 PS </TD><TD> X  </TD><TD>  X</TD>

</TD><TD> also known as <CODE>VOB</CODE> file
</TR>
<TR><TD>MPEG2 TS </TD><TD>    </TD><TD>  X</TD>

</TD><TD> also known as DVB Transport Stream
</TR>
<TR><TD>ASF</TD><TD> X </TD><TD> X</TD>

</TR>
<TR><TD>AVI</TD><TD> X </TD><TD> X</TD>

</TR>
<TR><TD>WAV</TD><TD> X </TD><TD> X</TD>

</TR>
<TR><TD>Macromedia Flash</TD><TD> X </TD><TD> X</TD>

</TD><TD> Only embedded audio is decoded
</TR>
<TR><TD>Real Audio and Video </TD><TD> X </TD><TD> X</TD>

</TR>
<TR><TD>PGM, YUV, PPM, JPEG images </TD><TD> X </TD><TD> X</TD>

</TR>
<TR><TD>Animated GIF </TD><TD> X </TD><TD></TD>

</TD><TD> Only uncompressed GIFs are generated
</TR>
<TR><TD>Raw AC3 </TD><TD> X  </TD><TD>  X</TD>

</TR>
<TR><TD>Raw MJPEG </TD><TD> X  </TD><TD>  X</TD>

</TR>
<TR><TD>Raw MPEG video </TD><TD> X  </TD><TD>  X</TD>

</TR>
<TR><TD>Raw PCM8/16 bits, mulaw/Alaw</TD><TD> X  </TD><TD>  X</TD>

</TR>
<TR><TD>SUN AU format </TD><TD> X  </TD><TD>  X</TD>

</TR>
<TR><TD>Quicktime        </TD><TD>   </TD><TD>  X</TD>

</TR>
<TR><TD>MPEG4            </TD><TD>  </TD><TD>  X</TD>

</TD><TD> MPEG4 is a variant of Quicktime
</TR>
<TR><TD>Raw MPEG4 video  </TD><TD>  </TD><TD>  X</TD>

</TD><TD> Only small files are supported.
</TR>
<TR><TD>DV               </TD><TD>  </TD><TD> X</TD>

</TD><TD> Only the video track is decoded.
</TR></TABLE>

<P>
<CODE>X</CODE> means that the encoding (resp. decoding) is supported.


<H2><A NAME="SEC15" HREF="ffmpeg-doc.html#TOC15">5.2 Video Codecs</A></H2>

<TABLE BORDER>

<TR><TD>Supported Codec </TD><TD> Encoding </TD><TD> Decoding </TD><TD> Comments</TD>

</TR>
<TR><TD>MPEG1 video            </TD><TD>  X  </TD><TD>  X</TD>

</TR>
<TR><TD>MPEG2 video            </TD><TD>     </TD><TD>  X</TD>

</TR>
<TR><TD>MPEG4                  </TD><TD>  X  </TD><TD>  X </TD><TD> Also known as DIVX4/5</TD>

</TR>
<TR><TD>MSMPEG4 V1             </TD><TD>  X  </TD><TD>  X</TD>

</TR>
<TR><TD>MSMPEG4 V2             </TD><TD>  X  </TD><TD>  X</TD>

</TR>
<TR><TD>MSMPEG4 V3             </TD><TD>  X  </TD><TD>  X </TD><TD> Also known as DIVX3</TD>

</TR>
<TR><TD>WMV7                   </TD><TD>  X  </TD><TD>  X</TD>

</TR>
<TR><TD>H263(+)                </TD><TD>  X  </TD><TD>  X </TD><TD> Also known as Real Video 1.0</TD>

</TR>
<TR><TD>MJPEG                  </TD><TD>  X  </TD><TD>  X</TD>

</TR>
<TR><TD>DV                     </TD><TD>     </TD><TD>  X</TD>

</TR></TABLE>

<P>
<CODE>X</CODE> means that the encoding (resp. decoding) is supported.


<P>
Check at <A HREF="http://www.mplayerhq.hu/~michael/codec-features.html">http://www.mplayerhq.hu/~michael/codec-features.html</A> to
get a precise comparison of FFmpeg MPEG4 codec compared to the other
solutions.


<H2><A NAME="SEC16" HREF="ffmpeg-doc.html#TOC16">5.3 Audio Codecs</A></H2>

<TABLE BORDER>

<TR><TD>Supported Codec </TD><TD> Encoding </TD><TD> Decoding </TD><TD> Comments</TD>

</TR>
<TR><TD>MPEG audio layer 2     </TD><TD>  IX  </TD><TD>  IX</TD>

</TR>
<TR><TD>MPEG audio layer 1/3   </TD><TD> IX   </TD><TD>  IX</TD>

</TD><TD> MP3 encoding is supported thru the external library LAME
</TR>
<TR><TD>AC3                    </TD><TD>  IX  </TD><TD>  X</TD>

</TD><TD> liba52 is used internally for decoding.
</TR>
<TR><TD>Vorbis                 </TD><TD>  X   </TD><TD></TD>

</TD><TD> encoding is supported thru the external library libvorbis.
</TR></TABLE>

<P>
<CODE>X</CODE> means that the encoding (resp. decoding) is supported.


<P>
<CODE>I</CODE> means that an integer only version is available too (ensures highest
performances on systems without hardware floating point support).


<H1><A NAME="SEC17" HREF="ffmpeg-doc.html#TOC17">6. Platform Specific information</A></H1>


<H2><A NAME="SEC18" HREF="ffmpeg-doc.html#TOC18">6.1 Linux</A></H2>

<P>
ffmpeg should be compiled with at least GCC 2.95.3. GCC 3.2 is the
prefered compiler now for ffmpeg. All futur optimizations will depend on
features only found in GCC 3.2.


<H2><A NAME="SEC19" HREF="ffmpeg-doc.html#TOC19">6.2 BSD</A></H2>


<H2><A NAME="SEC20" HREF="ffmpeg-doc.html#TOC20">6.3 Windows</A></H2>


<H2><A NAME="SEC21" HREF="ffmpeg-doc.html#TOC21">6.4 MacOS X</A></H2>


<H2><A NAME="SEC22" HREF="ffmpeg-doc.html#TOC22">6.5 BeOS</A></H2>

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


<P>
Old stuff:


<P>
François Revol - revol at free dot fr - April 2002


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


<P>
ffserver is broken (needs poll() implementation).


<P>
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)


<H1><A NAME="SEC23" HREF="ffmpeg-doc.html#TOC23">7. Developpers Guide</A></H1>


<H2><A NAME="SEC24" HREF="ffmpeg-doc.html#TOC24">7.1 API</A></H2>

<UL>
<LI>libavcodec is the library containing the codecs (both encoding and

  decoding). See <TT>`libavcodec/apiexample.c'</TT> to see how to use it.

<LI>libavformat is the library containing the file formats handling (mux and

  demux code for several formats). (no example yet, the API is likely to
  evolve).
</UL>


<H2><A NAME="SEC25" HREF="ffmpeg-doc.html#TOC25">7.2 Integrating libavcodec or libavformat in your program</A></H2>

<P>
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.


<P>
You can use libavcodec or libavformat in your commercial program, but
<EM>any patch you make must be published</EM>. The best way to proceed is
to send your patches to the ffmpeg mailing list.


<H2><A NAME="SEC26" HREF="ffmpeg-doc.html#TOC26">7.3 Coding Rules</A></H2>

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


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


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


<P>
Comments: for functions visible from other modules, use the JavaDoc
format (see examples in <TT>`libav/utils.c'</TT>) so that a documentation
can be generated automatically.


<H2><A NAME="SEC27" HREF="ffmpeg-doc.html#TOC27">7.4 Submitting patches</A></H2>

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


<P>
Run the regression tests before submitting a patch so that you can
verify that there is no big problems.


<P>
Except if your patch is really big and adds an important feature, by
submitting it to me, you accept implicitely to put it under my
copyright. I prefer to do this to avoid potential problems if
licensing of ffmpeg changes.


<P>
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 
<A HREF="http://lists.sourceforge.net/lists/listinfo/ffmpeg-devel">http://lists.sourceforge.net/lists/listinfo/ffmpeg-devel</A>


<H2><A NAME="SEC28" HREF="ffmpeg-doc.html#TOC28">7.5 Regression tests</A></H2>

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


<P>
The regression test build a synthetic video stream and a synthetic
audio stream. Then there 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.


<P>
Run 'make test' to test all the codecs.


<P>
Run 'make libavtest' to test all the codecs.


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


<P><HR><P>
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