Split developer documentation off from general documentation.

Originally committed as revision 19269 to svn://svn.ffmpeg.org/ffmpeg/trunk

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+\input texinfo @c -*- texinfo -*-
+
+@settitle Developer Documentation
+@titlepage
+@sp 7
+@center @titlefont{Developer Documentation}
+@sp 3
+@end titlepage
+
+
+@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.
+
+@node 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 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.
+@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 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.
+@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.
+
+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.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.
+
+@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 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 the
+    documentation?
+@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 "svn add" the appropriate files before commiting?
+@end enumerate
+
+@section patch submission checklist
+
+@enumerate
+@item
+    Do the regression tests pass with the patch applied?
+@item
+    Does @code{make checkheaders} pass with the patch applied?
+@item
+    Is the patch a unified diff?
+@item
+    Is the patch against latest FFmpeg SVN?
+@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
+    Is the patch created from the root of the source tree, so it can be
+    applied with @code{patch -p0}?
+@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.
+@item
+    Did you provide a suggestion for a clear commit log message?
+@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 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.
+
+@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 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].
+
+@bye