General Documentation: 1. external libraries

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# 1. external libraries

FFmpeg can be hooked up with a number of external libraries to add support for more formats. None of them are used by default, their use has to be explicitly requested by passing the appropriate flags to ``./configure'`.

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## 1.1 AMR

AMR comes in two different flavors, WB and NB. FFmpeg can make use of the AMR WB (floating-point mode) and the AMR NB (floating-point mode) reference decoders and encoders.

Go to http://www.penguin.cz/~utx/amr and follow the instructions for installing the libraries. Then pass `--enable-libamr-nb` and/or `--enable-libamr-wb` to configure to enable the libraries.

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# 2. Supported File Formats and Codecs

You can use the `-formats` option to have an exhaustive list.

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## 2.1 File Formats

FFmpeg supports the following file formats through the `libavformat` library:

Supported File Format | Encoding | Decoding | Comments
MPEG audio | X | X
MPEG-1 systems | X | X | muxed audio and video
MPEG-2 PS | X | X | also known as `VOB` file
MPEG-2 TS |  | X | also known as DVB Transport Stream
ASF | X | X
AVI | X | X
WAV | X | X
Macromedia Flash | X | X | Only embedded audio is decoded.
FLV | X | X | Macromedia Flash video files
Real Audio and Video | X | X
Raw AC3 | X | X
Raw MJPEG | X | X
Raw MPEG video | X | X
Raw PCM8/16 bits, mulaw/Alaw | X | X
Raw CRI ADX audio | X | X
Raw Shorten audio |  | X
SUN AU format | X | X
NUT | X | X | NUT Open Container Format
QuickTime | X | X
MPEG-4 | X | X | MPEG-4 is a variant of QuickTime.
Raw MPEG4 video | X | X
DV | X | X
4xm |  | X | 4X Technologies format, used in some games.
Playstation STR |  | X
Id RoQ | X | X | Used in Quake III, Jedi Knight 2, other computer games.
Interplay MVE |  | X | Format used in various Interplay computer games.
WC3 Movie |  | X | Multimedia format used in Origin's Wing Commander III computer game.
Sega FILM/CPK |  | X | Used in many Sega Saturn console games.
Westwood Studios VQA/AUD |  | X | Multimedia formats used in Westwood Studios games.
Id Cinematic (.cin) |  | X | Used in Quake II.
FLIC format |  | X | .fli/.flc files
Sierra VMD |  | X | Used in Sierra CD-ROM games.
Sierra Online |  | X | .sol files used in Sierra Online games.
Matroska | X | X
Electronic Arts Multimedia |  | X | Used in various EA games; files have extensions like WVE and UV2.
Nullsoft Video (NSV) format |  | X
ADTS AAC audio | X | X
Creative VOC | X | X | Created for the Sound Blaster Pro.
American Laser Games MM |  | X | Multimedia format used in games like Mad Dog McCree
AVS |  | X | Multimedia format used by the Creature Shock game.
Smacker |  | X | Multimedia format used by many games.
GXF | X | X | General eXchange Format SMPTE 360M, used by Thomson Grass Valley playout servers.
CIN |  | X | Multimedia format used by Delphine Software games.
MXF |  | X | Material eXchange Format SMPTE 377M, used by D-Cinema, broadcast industry.
SEQ |  | X | Tiertex .seq files used in the DOS CDROM version of the game Flashback.
DXA |  | X | This format is used in non-Windows version of Feeble Files game and different game cutscenes repacked for use with ScummVM.
THP |  | X | Used on the Nintendo GameCube.
C93 |  | X | Used in the game Cyberia from Interplay.
Bethsoft VID |  | X | Used in some games from Bethesda Softworks.
CRYO APC |  | X | Audio format used in some games by CRYO Interactive Entertainment.
Monkey's Audio |  | X

`X` means that encoding (resp. decoding) is supported.

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## 2.2 Image Formats

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

Supported Image Format | Encoding | Decoding | Comments
PGM, PPM | X | X
PAM | X | X | PAM is a PNM extension with alpha support.
PGMYUV | X | X | PGM with U and V components in YUV 4:2:0
JPEG | X | X | Progressive JPEG is not supported.
.Y.U.V | X | X | one raw file per component
animated GIF | X | X | Only uncompressed GIFs are generated.
PNG | X | X | 2 bit and 4 bit/pixel not supported yet.
Targa |  | X | Targa (.TGA) image format.
TIFF | X | X | YUV, JPEG and some extension is not supported yet.
SGI | X | X | SGI RGB image format
PTX |  | X | V.Flash PTX format

`X` means that encoding (resp. decoding) is supported.

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## 2.3 Video Codecs

Supported Codec | Encoding | Decoding | Comments
MPEG-1 video | X | X
MPEG-2 video | X | X
MPEG-4 | X | X
MSMPEG4 V1 | X | X
MSMPEG4 V2 | X | X
MSMPEG4 V3 | X | X
WMV7 | X | X
WMV8 | X | X | not completely working
WMV9 |  | X | not completely working
VC1 |  | X
H.261 | X | X
H.263(+) | X | X | also known as RealVideo 1.0
H.264 |  | X
RealVideo 1.0 | X | X
RealVideo 2.0 | X | X
MJPEG | X | X
lossless MJPEG | X | X
JPEG-LS | X | X | fourcc: MJLS, lossless and near-lossless is supported
Apple MJPEG-B |  | X
Sunplus MJPEG |  | X | fourcc: SP5X
DV | X | X
HuffYUV | X | X
FFmpeg Video 1 | X | X | experimental lossless codec (fourcc: FFV1)
FFmpeg Snow | X | X | experimental wavelet codec (fourcc: SNOW)
Asus v1 | X | X | fourcc: ASV1
Asus v2 | X | X | fourcc: ASV2
Creative YUV |  | X | fourcc: CYUV
Sorenson Video 1 | X | X | fourcc: SVQ1
Sorenson Video 3 |  | X | fourcc: SVQ3
On2 VP3 |  | X | still experimental
On2 VP5 |  | X | fourcc: VP50
On2 VP6 |  | X | fourcc: VP60,VP61,VP62
Theora | X | X | still experimental
Intel Indeo 3 |  | X
FLV | X | X | Sorenson H.263 used in Flash
Flash Screen Video | X | X | fourcc: FSV1
ATI VCR1 |  | X | fourcc: VCR1
ATI VCR2 |  | X | fourcc: VCR2
Cirrus Logic AccuPak |  | X | fourcc: CLJR
4X Video |  | X | Used in certain computer games.
Sony Playstation MDEC |  | X
Id RoQ | X | X | Used in Quake III, Jedi Knight 2, other computer games.
Xan/WC3 |  | X | Used in Wing Commander III .MVE files.
Interplay Video |  | X | Used in Interplay .MVE files.
Apple Animation | X | X | fourcc: 'rle '
Apple Graphics |  | X | fourcc: 'smc '
Apple Video |  | X | fourcc: rpza
Apple QuickDraw |  | X | fourcc: qdrw
Cinepak |  | X
Microsoft RLE |  | X
Microsoft Video-1 |  | X
Westwood VQA |  | X
Id Cinematic Video |  | X | Used in Quake II.
Planar RGB |  | X | fourcc: 8BPS
FLIC video |  | X
Duck TrueMotion v1 |  | X | fourcc: DUCK
Duck TrueMotion v2 |  | X | fourcc: TM20
VMD Video |  | X | Used in Sierra VMD files.
MSZH |  | X | Part of LCL
ZLIB | X | X | Part of LCL, encoder experimental
TechSmith Camtasia |  | X | fourcc: TSCC
IBM Ultimotion |  | X | fourcc: ULTI
Miro VideoXL |  | X | fourcc: VIXL
QPEG |  | X | fourccs: QPEG, Q1.0, Q1.1
LOCO |  | X |
Winnov WNV1 |  | X |
Autodesk Animator Studio Codec |  | X | fourcc: AASC
Fraps FPS1 |  | X |
CamStudio |  | X | fourcc: CSCD
American Laser Games Video |  | X | Used in games like Mad Dog McCree
ZMBV | X | X | Encoder works only on PAL8
AVS Video |  | X | Video encoding used by the Creature Shock game.
Smacker Video |  | X | Video encoding used in Smacker.
RTjpeg |  | X | Video encoding used in NuppelVideo files.
KMVC |  | X | Codec used in Worms games.
VMware Video |  | X | Codec used in videos captured by VMware.
Cin Video |  | X | Codec used in Delphine Software games.
Tiertex Seq Video |  | X | Codec used in DOS CDROM FlashBack game.
DXA Video |  | X | Codec originally used in Feeble Files game.
AVID DNxHD |  | X | aka SMPTE VC3
C93 Video |  | X | Codec used in Cyberia game.
THP |  | X | Used on the Nintendo GameCube.
Bethsoft VID |  | X | Used in some games from Bethesda Softworks.
Renderware TXD |  | X | Texture dictionaries used by the Renderware Engine.
AMV |  | X | Used in Chinese MP3 players.

`X` means that encoding (resp. decoding) is supported.

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## 2.4 Audio Codecs

Supported Codec | Encoding | Decoding | Comments
MPEG audio layer 2 | IX | IX
MPEG audio layer 1/3 | IX | IX | MP3 encoding is supported through the external library LAME.
AC3 | IX | IX | liba52 is used internally for decoding.
Vorbis | X | X
WMA V1/V2 | X | X
AAC | X | X | Supported through the external library libfaac/libfaad.
Microsoft ADPCM | X | X
AMV IMA ADPCM |  | X | Used in AMV files
MS IMA ADPCM | X | X
QT IMA ADPCM |  | X
4X IMA ADPCM |  | X
G.726 ADPCM | X | X
Duck DK3 IMA ADPCM |  | X | Used in some Sega Saturn console games.
Duck DK4 IMA ADPCM |  | X | Used in some Sega Saturn console games.
Westwood Studios IMA ADPCM |  | X | Used in Westwood Studios games like Command and Conquer.
SMJPEG IMA ADPCM |  | X | Used in certain Loki game ports.
CD-ROM XA ADPCM |  | X
CRI ADX ADPCM | X | X | Used in Sega Dreamcast games.
Electronic Arts ADPCM |  | X | Used in various EA titles.
Creative ADPCM |  | X | 16 -> 4, 8 -> 4, 8 -> 3, 8 -> 2
THP ADPCM |  | X | Used on the Nintendo GameCube.
RA144 |  | X | Real 14400 bit/s codec
RA288 |  | X | Real 28800 bit/s codec
RADnet | X | IX | Real low bitrate AC3 codec, liba52 is used for decoding.
AMR-NB | X | X | Supported through an external library.
AMR-WB | X | X | Supported through an external library.
DV audio |  | X
Id RoQ DPCM | X | X | Used in Quake III, Jedi Knight 2, other computer games.
Interplay MVE DPCM |  | X | Used in various Interplay computer games.
Xan DPCM |  | X | Used in Origin's Wing Commander IV AVI files.
Sierra Online DPCM |  | X | Used in Sierra Online game audio files.
Apple MACE 3 |  | X
Apple MACE 6 |  | X
FLAC lossless audio | X | X
Shorten lossless audio |  | X
Apple lossless audio |  | X | QuickTime fourcc 'alac'
FFmpeg Sonic | X | X | experimental lossy/lossless codec
Qdesign QDM2 |  | X | there are still some distortions
Real COOK |  | X | All versions except 5.1 are supported
DSP Group TrueSpeech |  | X
True Audio (TTA) |  | X
Smacker Audio |  | X
WavPack Audio |  | X
Cin Audio |  | X | Codec used in Delphine Software games.
Intel Music Coder |  | X
Musepack |  | X | Only SV7 is supported
DT$ Coherent Audio |  | X
ATRAC 3 |  | X
Monkey's Audio |  | X | Only versions 3.97-3.99 are supported

`X` means that encoding (resp. decoding) is supported.

`I` means that an integer-only version is available, too (ensures high performance on systems without hardware floating point support).

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# 3. Platform Specific information

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## 3.1 BSD

BSD make will not build FFmpeg, you need to install and use GNU Make (``gmake'`).

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## 3.2 Windows

To get help and instructions for using FFmpeg under Windows, check out the FFmpeg Windows Help Forum at http://arrozcru.no-ip.org/ffmpeg/.

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### 3.2.1 Native Windows compilation

Notes:

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### 3.2.2 Visual C++ compatibility

FFmpeg will not compile under Visual C++ - and it has too many dependencies on the GCC compiler to make a port viable. However, if you want to use the FFmpeg libraries in your own applications, you can still compile those applications using Visual C++. An important restriction to this is that you have to use the dynamically linked versions of the FFmpeg libraries (i.e. the DLLs), and you have to make sure that Visual-C++-compatible import libraries are created during the FFmpeg build process.

This description of how to use the FFmpeg libraries with Visual C++ is based on Visual C++ 2005 Express Edition Beta 2. If you have a different version, you might have to modify the procedures slightly.

Here are the step-by-step instructions for building the FFmpeg libraries so they can be used with Visual C++:

1. Install Visual C++ (if you have not done so already).
2. Install MinGW and MSYS as described above.
3. Add a call to ``vcvars32.bat'` (which sets up the environment variables for the Visual C++ tools) as the first line of ``msys.bat'`. The standard location for ``vcvars32.bat'` is ``C:\Program Files\Microsoft Visual Studio 8\VC\bin\vcvars32.bat'`, and the standard location for ``msys.bat'` is ``C:\msys\1.0\msys.bat'`. If this corresponds to your setup, add the following line as the first line of ``msys.bat'`:

   `call "C:\Program Files\Microsoft Visual Studio 8\VC\bin\vcvars32.bat"`

4. Start the MSYS shell (file ``msys.bat'`) and type `link.exe`. If you get a help message with the command line options of `link.exe`, this means your environment variables are set up correctly, the Microsoft linker is on the path and will be used by FFmpeg to create Visual-C++-compatible import libraries.
5. Extract the current version of FFmpeg and change to the FFmpeg directory.
6. Type the command `./configure --enable-shared --disable-static --enable-memalign-hack` to configure and, if that did not produce any errors, type `make` to build FFmpeg.
7. The subdirectories ``libavformat'`, ``libavcodec'`, and ``libavutil'` should now contain the files ``avformat.dll'`, ``avformat.lib'`, ``avcodec.dll'`, ``avcodec.lib'`, ``avutil.dll'`, and ``avutil.lib'`, respectively. Copy the three DLLs to your System32 directory (typically ``C:\Windows\System32'`).

And here is how to use these libraries with Visual C++:

1. Create a new console application ("File / New / Project") and then select "Win32 Console Application". On the appropriate page of the Application Wizard, uncheck the "Precompiled headers" option.
2. Write the source code for your application, or, for testing, just copy the code from an existing sample application into the source file that Visual C++ has already created for you. (Note that your source filehas to have a `.cpp` extension; otherwise, Visual C++ will not compile the FFmpeg headers correctly because in C mode, it does not recognize the `inline` keyword.) For example, you can copy ``output_example.c'` from the FFmpeg distribution (but you will have to make minor modifications so the code will compile under C++, see below).
3. Open the "Project / Properties" dialog box. In the "Configuration" combo box, select "All Configurations" so that the changes you make will affect both debug and release builds. In the tree view on the left hand side, select "C/C++ / General", then edit the "Additional Include Directories" setting to contain the complete paths to the ``libavformat'`, ``libavcodec'`, and ``libavutil'` subdirectories of your FFmpeg directory. Note that the directories have to be separated using semicolons. Now select "Linker / General" from the tree view and edit the "Additional Library Directories" setting to contain the same three directories.
4. Still in the "Project / Properties" dialog box, select "Linker / Input" from the tree view, then add the files ``avformat.lib'`, ``avcodec.lib'`, and ``avutil.lib'` to the end of the "Additional Dependencies". Note that the names of the libraries have to be separated using spaces.
5. Now, select "C/C++ / Code Generation" from the tree view. Select "Debug" in the "Configuration" combo box. Make sure that "Runtime Library" is set to "Multi-threaded Debug DLL". Then, select "Release" in the "Configuration" combo box and make sure that "Runtime Library" is set to "Multi-threaded DLL".
6. Click "OK" to close the "Project / Properties" dialog box and build the application. Hopefully, it should compile and run cleanly. If you used ``output_example.c'` as your sample application, you will get a few compiler errors, but they are easy to fix. The first type of error occurs because Visual C++ does not allow an `int` to be converted to an `enum` without a cast. To solve the problem, insert the required casts (this error occurs once for a `CodecID` and once for a `CodecType`). The second type of error occurs because C++ requires the return value of `malloc` to be cast to the exact type of the pointer it is being assigned to. Visual C++ will complain that, for example, `(void *)` is being assigned to `(uint8_t *)` without an explicit cast. So insert an explicit cast in these places to silence the compiler. The third type of error occurs because the `snprintf` library function is called `_snprintf` under Visual C++. So just add an underscore to fix the problem. With these changes, ``output_example.c'` should compile under Visual C++, and the resulting executable should produce valid video files.

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### 3.2.3 Cross compilation for Windows with Linux

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

Then configure FFmpeg with the following options:

    ./configure --target-os=mingw32 --cross-prefix=i386-mingw32msvc-

(you can change the cross-prefix according to the prefix chosen for the MinGW tools).

Then you can easily test FFmpeg with Wine (http://www.winehq.com/).

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### 3.2.4 Compilation under Cygwin

Cygwin works very much like Unix.

Just install your Cygwin with all the "Base" packages, plus the following "Devel" ones:

    binutils, gcc-core, make, subversion

Do not install binutils-20060709-1 (they are buggy on shared builds); use binutils-20050610-1 instead.

Then run

    ./configure --enable-static --disable-shared

to make a static build or

    ./configure --enable-shared --disable-static

to build shared libraries.

If you want to build FFmpeg with additional libraries, download Cygwin "Devel" packages for Ogg and Vorbis from any Cygwin packages repository and/or SDL, xvid, faac, faad2 packages from Cygwin Ports, (http://cygwinports.dotsrc.org/).

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### 3.2.5 Crosscompilation for Windows under Cygwin

With Cygwin you can create Windows binaries that do not need the cygwin1.dll.

Just install your Cygwin as explained before, plus these additional "Devel" packages:

    gcc-mingw-core, mingw-runtime, mingw-zlib

and add some special flags to your configure invocation.

For a static build run

    ./configure --target-os=mingw32 --enable-memalign-hack --enable-static --disable-shared --extra-cflags=-mno-cygwin --extra-libs=-mno-cygwin

and for a build with shared libraries

    ./configure --target-os=mingw32 --enable-memalign-hack --enable-shared --disable-static --extra-cflags=-mno-cygwin --extra-libs=-mno-cygwin

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## 3.3 BeOS

BeOS support is broken in mysterious ways.

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# 4. Developers Guide

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## 4.1 API

- libavcodec is the library containing the codecs (both encoding and decoding). Look at ``libavcodec/apiexample.c'` to see how to use it.
- libavformat is the library containing the file format handling (mux and demux code for several formats). Look at ``ffplay.c'` to use it in a player. See ``output_example.c'` to use it to generate audio or video streams.

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## 4.2 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 any patch you make must be published. The best way to proceed is to send your patches to the FFmpeg mailing list.

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## 4.3 Coding Rules

FFmpeg is programmed in the ISO C90 language with a few additional features from ISO C99, namely:

- the ``inline'` keyword;
- ``//'` comments;
- designated struct initializers (``struct s x = { .i = 17 };'`)
- compound literals (``x = (struct s) { 17, 23 };'`)

These features are supported by all compilers we care about, so we will not accept patches to remove their use unless they absolutely do not impair clarity and performance.

All code must compile with GCC 2.95 and GCC 3.3. Currently, FFmpeg also compiles with several other compilers, such as the Compaq ccc compiler or Sun Studio 9, and we would like to keep it that way unless it would be exceedingly involved. To ensure compatibility, please do not use any additional C99 features or GCC extensions. Especially watch out for:

- mixing statements and declarations;
- ``long long'` (use ``int64_t'` instead);
- ``__attribute__'` not protected by ``#ifdef __GNUC__'` or similar;
- GCC statement expressions (``(x = ({ int y = 4; y; })'`).

Indent size is 4. The presentation is the one specified by 'indent -i4 -kr -nut'. The TAB character is forbidden outside of Makefiles as is any form of trailing whitespace. Commits containing either will be rejected by the Subversion repository.

The main priority in FFmpeg is simplicity and small code size in order to minimize the bug count.

Comments: Use the JavaDoc/Doxygen format (see examples below) so that code documentation can be generated automatically. All nontrivial functions should have a comment above them explaining what the function does, even if it is just one sentence. All structures and their member variables should be documented, too.

    /**
     * @file mpeg.c
     * MPEG codec.
     * @author ...
     */

    /**
     * Summary sentence.
     * more text ...
     * ...
     */
    typedef struct Foobar{
        int var1; /**< var1 description */
        int var2; ///< var2 description
        /** var3 description */
        int var3;
    } Foobar;

    /**
     * Summary sentence.
     * more text ...
     * ...
     * @param my_parameter description of my_parameter
     * @return return value description
     */
    int myfunc(int my_parameter)
    ...

fprintf and printf are forbidden in libavformat and libavcodec, please use av_log() instead.

Casts should be used only when necessary. Unneeded parentheses should also be avoided if they don't make the code easier to understand.

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## 4.4 Development Policy

1. Contributions should be licensed under the LGPL 2.1, including an "or any later version" clause, or the MIT license. GPL 2 including an "or any later version" clause is also acceptable, but LGPL is preferred.
2. You must not commit code which breaks FFmpeg! (Meaning unfinished but enabled code which breaks compilation or compiles but does not work or breaks the regression tests) You can commit unfinished stuff (for testing etc), but it must be disabled (#ifdef etc) by default so it does not interfere with other developers' work.
3. You do not have to over-test things. If it works for you, and you think it should work for others, then commit. If your code has problems (portability, triggers compiler bugs, unusual environment etc) they will be reported and eventually fixed.
4. Do not commit unrelated changes together, split them into self-contained pieces. Also do not forget that if part B depends on part A, but A does not depend on B, then A can and should be committed first and separate from B. Keeping changes well split into self-contained parts makes reviewing and understanding them on the commit log mailing list easier. This also helps in case of debugging later on. Also if you have doubts about splitting or not splitting, do not hesitate to ask/discuss it on the developer mailing list.
5. Do not change behavior of the program (renaming options etc) without first discussing it on the ffmpeg-devel mailing list. Do not remove functionality from the code. Just improve!

   Note: Redundant code can be removed.

6. Do not commit changes to the build system (Makefiles, configure script) which change behavior, defaults etc, without asking first. The same applies to compiler warning fixes, trivial looking fixes and to code maintained by other developers. We usually have a reason for doing things the way we do. Send your changes as patches to the ffmpeg-devel mailing list, and if the code maintainers say OK, you may commit. This does not apply to files you wrote and/or maintain.
7. We refuse source indentation and other cosmetic changes if they are mixed with functional changes, such commits will be rejected and removed. Every developer has his own indentation style, you should not change it. Of course if you (re)write something, you can use your own style, even though we would prefer if the indentation throughout FFmpeg was consistent (Many projects force a given indentation style - we do not.). If you really need to make indentation changes (try to avoid this), separate them strictly from real changes.

   NOTE: If you had to put if(){ .. } over a large (> 5 lines) chunk of code, then either do NOT change the indentation of the inner part within (do not move it to the right)! or do so in a separate commit

8. Always fill out the commit log message. Describe in a few lines what you changed and why. You can refer to mailing list postings if you fix a particular bug. Comments such as "fixed!" or "Changed it." are unacceptable.
9. If you apply a patch by someone else, include the name and email address in the log message. Since the ffmpeg-cvslog mailing list is publicly archived you should add some SPAM protection to the email address. Send an answer to ffmpeg-devel (or wherever you got the patch from) saying that you applied the patch.
10. When applying patches that have been discussed (at length) on the mailing list, reference the thread in the log message.
11. Do NOT commit to code actively maintained by others without permission. Send a patch to ffmpeg-devel instead. If no one answers within a reasonable timeframe (12h for build failures and security fixes, 3 days small changes, 1 week for big patches) then commit your patch if you think it is OK. Also note, the maintainer can simply ask for more time to review!
12. Subscribe to the ffmpeg-cvslog mailing list. The diffs of all commits are sent there and reviewed by all the other developers. Bugs and possible improvements or general questions regarding commits are discussed there. We expect you to react if problems with your code are uncovered.
13. Update the documentation if you change behavior or add features. If you are unsure how best to do this, send a patch to ffmpeg-devel, the documentation maintainer(s) will review and commit your stuff.
14. Try to keep important discussions and requests (also) on the public developer mailing list, so that all developers can benefit from them.
15. Never write to unallocated memory, never write over the end of arrays, always check values read from some untrusted source before using them as array index or other risky things.
16. Remember to check if you need to bump versions for the specific libav parts (libavutil, libavcodec, libavformat) you are changing. You need to change the version integer and the version string. Incrementing the first component means no backward compatibility to previous versions (e.g. removal of a function from the public API). Incrementing the second component means backward compatible change (e.g. addition of a function to the public API). Incrementing the third component means a noteworthy binary compatible change (e.g. encoder bug fix that matters for the decoder).
17. If you add a new codec, remember to update the changelog, add it to the supported codecs table in the documentation and bump the second component of the ``libavcodec'` version number appropriately. If it has a fourcc, add it to ``libavformat/avienc.c'`, even if it is only a decoder.
18. Do not change code to hide warnings without ensuring that the underlying logic is correct and thus the warning was inappropriate.
19. If you add a new file, give it a proper license header. Do not copy and paste it from a random place, use an existing file as template.

We think our rules are not too hard. If you have comments, contact us.

Note, these rules are mostly borrowed from the MPlayer project.

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## 4.5 Submitting patches

First, (see section Coding Rules) above if you did not yet.

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

Also please do not submit a patch which contains several unrelated changes. Split it into separate, self-contained pieces. This does not mean splitting file by file. Instead, make the patch as small as possible while still keeping it as a logical unit that contains an individual change, even if it spans multiple files. This makes reviewing your patches much easier for us and greatly increases your chances of getting your patch applied.

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 will not be trashed during transmission) to the ffmpeg-devel mailing list, see http://lists.mplayerhq.hu/mailman/listinfo/ffmpeg-devel

It also helps quite a bit if you tell us what the patch does (for example 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant and has no lrint()')

Also please if you send several patches, send each patch as a separate mail, do not attach several unrelated patches to the same mail.

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## 4.6 patch submission checklist

1. Do the regression tests pass with the patch applied?
2. Is the patch a unified diff?
3. Is the patch against latest FFmpeg SVN?
4. Are you subscribed to ffmpeg-dev? (the list is subscribers only due to spam)
5. Have you checked that the changes are minimal, so that the same cannot be achieved with a smaller patch and/or simpler final code?
6. If the change is to speed critical code, did you benchmark it?
7. If you did any benchmarks, did you provide them in the mail?
8. Have you checked that the patch does not introduce buffer overflows or other security issues?
9. Is the patch created from the root of the source tree, so it can be applied with `patch -p0`?
10. Does the patch not mix functional and cosmetic changes?
11. Did you add tabs or trailing whitespace to the code? Both are forbidden.
12. Is the patch attached to the email you send?
13. Is the mime type of the patch correct? It should be text/x-diff or text/x-patch or at least text/plain and not application/octet-stream.
14. If the patch fixes a bug, did you provide a verbose analysis of the bug?
15. If the patch fixes a bug, did you provide enough information, including a sample, so the bug can be reproduced and the fix can be verified? Note please do not attach samples >100k to mails but rather provide a URL, you can upload to ftp://upload.mplayerhq.hu
16. Did you provide a verbose summary about what the patch does change?
17. Did you provide a verbose explanation why it changes things like it does?
18. Did you provide a verbose summary of the user visible advantages and disadvantages if the patch is applied?
19. Did you provide an example so we can verify the new feature added by the patch easily?
20. If you added a new file, did you insert a license header? It should be taken from FFmpeg, not randomly copied and pasted from somewhere else.
21. You should maintain alphabetical order in alphabetically ordered lists as long as doing so does not break API/ABI compatibility.
22. Lines with similar content should be aligned vertically when doing so improves readability.
23. Did you provide a suggestion for a clear commit log message?

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## 4.7 Patch review process

All patches posted to ffmpeg-devel will be reviewed, unless they contain a clear note that the patch is not for SVN. Reviews and comments will be posted as replies to the patch on the mailing list. The patch submitter then has to take care of every comment, that can be by resubmitting a changed patch or by discussion. Resubmitted patches will themselves be reviewed like any other patch. If at some point a patch passes review with no comments then it is approved, that can for simple and small patches happen immediately while large patches will generally have to be changed and reviewed many times before they are approved. After a patch is approved it will be committed to the repository.

We will review all submitted patches, but sometimes we are quite busy so especially for large patches this can take several weeks.

When resubmitting patches, please do not make any significant changes not related to the comments received during review. Such patches will be rejected. Instead, submit significant changes or new features as separate patches.

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## 4.8 Regression tests

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

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

The regression tests then go 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 and formats.

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

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

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# About This Document

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