PeerStreamer

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

@settitle Developer Documentation

@titlepage

@center @titlefont{Developer Documentation}

@end titlepage

@top

@contents

@chapter Developers Guide

@section API

@itemize @bullet

@item libavcodec is the library containing the codecs (both encoding and

decoding). Look at @file{libavcodec/apiexample.c} to see how to use it.

@item libavformat is the library containing the file format handling (mux and

demux code for several formats). Look at @file{ffplay.c} to use it in a

player. See @file{libavformat/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.

@anchor{Coding Rules}

@section Coding Rules

FFmpeg is programmed in the ISO C90 language with a few additional

features from ISO C99, namely:

@itemize @bullet

@item

the @samp{inline} keyword;

@item

@samp{//} comments;

@item

designated struct initializers (@samp{struct s x = @{ .i = 17 @};})

@item

compound literals (@samp{x = (struct s) @{ 17, 23 @};})

@end itemize

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:

@itemize @bullet

@item

mixing statements and declarations;

@item

@samp{long long} (use @samp{int64_t} instead);

@item

@samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;

@item

GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).

@end itemize

Indent size is 4.

The presentation is one inspired 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 git 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.

@example

/**

 * @@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)

...

@end example

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.

@section Development Policy

@enumerate

@item

   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.

@item

   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.

@item

   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.

@item

   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.

@item

   Do not change behavior of the programs (renaming options etc) or public

   API or ABI 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.

@item

   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.

@item

   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

@item

   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.

@item

   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.

@item

   When applying patches that have been discussed (at length) on the mailing

   list, reference the thread in the log message.

@item

    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!

@item

    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.

@item

    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.

@item

    Try to keep important discussions and requests (also) on the public

    developer mailing list, so that all developers can benefit from them.

@item

    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.

@item

    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.

    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 or extension of an

    existing data structure).

    Incrementing the third component means a noteworthy binary compatible

    change (e.g. encoder bug fix that matters for the decoder).

@item

    Compiler warnings indicate potential bugs or code with bad style. If a type of

    warning always points to correct and clean code, that warning should

    be disabled, not the code changed.

    Thus the remaining warnings can either be bugs or correct code.

    If it is a bug, the bug has to be fixed. If it is not, the code should

    be changed to not generate a warning unless that causes a slowdown

    or obfuscates the code.

@item

    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.

@end enumerate

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

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

@section Submitting patches

First, (@pxref{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.

Use the patcheck tool of FFmpeg to check your patch.

The tool is located in the tools directory.

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

@url{http://lists.ffmpeg.org/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.

Your patch will be reviewed on the mailing list. You will likely be asked

to make some changes and are expected to send in an improved version that

incorporates the requests from the review. This process may go through

several iterations. Once your patch is deemed good enough, some developer

will pick it up and commit it to the official FFmpeg tree.

Give us a few days to react. But if some time passes without reaction,

send a reminder by email. Your patch should eventually be dealt with.

@section New codecs or formats checklist

@enumerate

@item

    Did you use av_cold for codec initialization and close functions?

@item

    Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or

    AVInputFormat/AVOutputFormat struct?

@item

    Did you bump the minor version number (and reset the micro version

    number) in @file{avcodec.h} or @file{avformat.h}?

@item

    Did you register it in @file{allcodecs.c} or @file{allformats.c}?

@item

    Did you add the CodecID to @file{avcodec.h}?

@item

    If it has a fourcc, did you add it to @file{libavformat/riff.c},

    even if it is only a decoder?

@item

    Did you add a rule to compile the appropriate files in the Makefile?

    Remember to do this even if you're just adding a format to a file that is

    already being compiled by some other rule, like a raw demuxer.

@item

    Did you add an entry to the table of supported formats or codecs in

    @file{doc/general.texi}?

@item

    Did you add an entry in the Changelog?

@item

    If it depends on a parser or a library, did you add that dependency in

    configure?

@item

    Did you "git add" the appropriate files before committing?

@end enumerate

@section patch submission checklist

@enumerate

@item

    Does 'make fate' pass with the patch applied?

@item

    Was the patch generated with git format-patch or send-email?

@item

    Did you sign off your patch? (git commit -s)

    See @url{http://kerneltrap.org/files/Jeremy/DCO.txt} for the meaning

    of sign off.

@item

    Did you provide a clear git commit log message?

@item

    Is the patch against latest FFmpeg git master branch?

@item

    Are you subscribed to ffmpeg-dev?

    (the list is subscribers only due to spam)

@item

    Have you checked that the changes are minimal, so that the same cannot be

    achieved with a smaller patch and/or simpler final code?

@item

    If the change is to speed critical code, did you benchmark it?

@item

    If you did any benchmarks, did you provide them in the mail?

@item

    Have you checked that the patch does not introduce buffer overflows or

    other security issues?

@item

    Did you test your decoder or demuxer against damaged data? If no, see

    tools/trasher and the noise bitstream filter. Your decoder or demuxer

    should not crash or end in a (near) infinite loop when fed damaged data.

@item

    Does the patch not mix functional and cosmetic changes?

@item

    Did you add tabs or trailing whitespace to the code? Both are forbidden.

@item

    Is the patch attached to the email you send?

@item

    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.

@item

    If the patch fixes a bug, did you provide a verbose analysis of the bug?

@item

    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.ffmpeg.org

@item

    Did you provide a verbose summary about what the patch does change?

@item

    Did you provide a verbose explanation why it changes things like it does?

@item

    Did you provide a verbose summary of the user visible advantages and

    disadvantages if the patch is applied?

@item

    Did you provide an example so we can verify the new feature added by the

    patch easily?

@item

    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.

@item

    You should maintain alphabetical order in alphabetically ordered lists as

    long as doing so does not break API/ABI compatibility.

@item

    Lines with similar content should be aligned vertically when doing so

    improves readability.

@end enumerate

@section Patch review process

All patches posted to ffmpeg-devel will be reviewed, unless they contain a

clear note that the patch is not for the git master branch.

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.

@section 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 output is checked immediately after each test

has run.

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. Commands like

'make regtest-mpeg2' can be used to run a single test. By default,

make will abort if any test fails. To run all tests regardless,

use make -k. To get a more verbose output, use 'make V=1 test' or

'make V=2 test'.

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].

@bye