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\input texinfo @c -*- texinfo -*-
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@settitle Developer Documentation
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@titlepage
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@center @titlefont{Developer Documentation}
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@end titlepage
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@top
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@contents
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@chapter Developers Guide
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@section API
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@itemize @bullet
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@item libavcodec is the library containing the codecs (both encoding and
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decoding). Look at @file{libavcodec/apiexample.c} to see how to use it.
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@item libavformat is the library containing the file format handling (mux and
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demux code for several formats). Look at @file{ffplay.c} to use it in a
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player. See @file{libavformat/output-example.c} to use it to generate
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audio or video streams.
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@end itemize
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@section Integrating libav in your program
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Shared libraries should be used whenever is possible in order to reduce
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the effort distributors have to pour to support programs and to ensure
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only the public api is used.
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You can use Libav in your commercial program, but you must abide to the
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license, LGPL or GPL depending on the specific features used, please refer
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to @url{http://libav.org/legal.html} for a quick checklist and to
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@url{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.GPLv2},
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@url{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.GPLv3},
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@url{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.LGPLv2.1},
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@url{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.LGPLv3} for the
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exact text of the licenses.
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Any modification to the source code can be suggested for inclusion.
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The best way to proceed is to send your patches to the Libav mailing list.
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@anchor{Coding Rules}
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@section Coding Rules
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Libav is programmed in the ISO C90 language with a few additional
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features from ISO C99, namely:
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@itemize @bullet
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@item
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the @samp{inline} keyword;
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@item
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@samp{//} comments;
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@item
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designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
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@item
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compound literals (@samp{x = (struct s) @{ 17, 23 @};})
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@end itemize
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These features are supported by all compilers we care about, so we will not
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accept patches to remove their use unless they absolutely do not impair
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clarity and performance.
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All code must compile with GCC 2.95 and GCC 3.3. Currently, Libav also
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compiles with several other compilers, such as the Compaq ccc compiler
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or Sun Studio 9, and we would like to keep it that way unless it would
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be exceedingly involved. To ensure compatibility, please do not use any
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additional C99 features or GCC extensions. Especially watch out for:
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@itemize @bullet
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@item
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mixing statements and declarations;
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@item
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@samp{long long} (use @samp{int64_t} instead);
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@item
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@samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;
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@item
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GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
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@end itemize
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Indent size is 4.
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The presentation is one inspired by 'indent -i4 -kr -nut'.
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The TAB character is forbidden outside of Makefiles as is any
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form of trailing whitespace. Commits containing either will be
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rejected by the git repository.
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The main priority in Libav is simplicity and small code size in order to
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minimize the bug count.
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Comments: Use the JavaDoc/Doxygen
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format (see examples below) so that code documentation
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can be generated automatically. All nontrivial functions should have a comment
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above them explaining what the function does, even if it is just one sentence.
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All structures and their member variables should be documented, too.
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@example
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/**
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 * @@file mpeg.c
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 * MPEG codec.
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 * @@author ...
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 */
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/**
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 * Summary sentence.
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 * more text ...
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 * ...
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 */
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typedef struct Foobar@{
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    int var1; /**< var1 description */
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    int var2; ///< var2 description
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    /** var3 description */
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    int var3;
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@} Foobar;
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/**
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 * Summary sentence.
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 * more text ...
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 * ...
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 * @@param my_parameter description of my_parameter
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 * @@return return value description
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 */
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int myfunc(int my_parameter)
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...
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@end example
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fprintf and printf are forbidden in libavformat and libavcodec,
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please use av_log() instead.
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Casts should be used only when necessary. Unneeded parentheses
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should also be avoided if they don't make the code easier to understand.
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@section Development Policy
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@enumerate
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@item
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   Contributions should be licensed under the LGPL 2.1, including an
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   "or any later version" clause, or the MIT license.  GPL 2 including
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   an "or any later version" clause is also acceptable, but LGPL is
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   preferred.
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@item
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   All the patches MUST be reviewed in the mailing list before they are
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   committed.
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@item
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   The Libav coding style should remain consistent. Changes to
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   conform will be suggested during the review or implemented on commit.
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@item
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   Patches should be generated using @code{git format-patch} or directly sent
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   using @code{git send-email}.
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   Please make sure you give the proper credit by setting the correct author
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   in the commit.
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@item
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   The commit message should have a short first line in the form of
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   @samp{topic: short description} as header, separated by a newline
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   from the body consting in few lines explaining the reason of the patch.
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   Referring to the issue on the bug tracker does not exempt to report an
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   excerpt of the bug.
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@item
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   Work in progress patches should be sent to the mailing list with the [WIP]
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   or the [RFC] tag.
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@item
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   Branches in public personal repos are advised as way to
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   work on issues collaboratively.
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@item
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   You do not have to over-test things. If it works for you and you think it
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   should work for others, send it to the mailing list for review.
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   If you have doubt about portability please state it in the submission so
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   people with specific hardware could test it.
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@item
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   Do not commit unrelated changes together, split them into self-contained
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   pieces. Also do not forget that if part B depends on part A, but A does not
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   depend on B, then A can and should be committed first and separate from B.
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   Keeping changes well split into self-contained parts makes reviewing and
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   understanding them on the commit log mailing list easier. This also helps
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   in case of debugging later on.
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@item
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   Patches that change behavior of the programs (renaming options etc) or
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   public API or ABI should be discussed in depth and possible few days should
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   pass between discussion and commit.
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   Changes to the build system (Makefiles, configure script) which alter
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   the expected behavior should be considered in the same regard.
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@item
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   When applying patches that have been discussed (at length) on the mailing
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   list, reference the thread in the log message.
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@item
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    Subscribe to the libav-devel and libav-commits mailing list.
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    Bugs and possible improvements or general questions regarding commits
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    are discussed on libav-devel. We expect you to react if problems with
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    your code are uncovered.
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@item
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    Update the documentation if you change behavior or add features. If you are
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    unsure how best to do this, send an [RFC] patch to libav-devel.
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@item
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    All discussions and decisions should be reported on the public developer
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    mailing list, so that there is a reference to them.
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    Other media (e.g. IRC) should be used for coordination and immediate
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    collaboration.
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@item
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    Never write to unallocated memory, never write over the end of arrays,
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    always check values read from some untrusted source before using them
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    as array index or other risky things. Always use valgrind to doublecheck.
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@item
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    Remember to check if you need to bump versions for the specific libav
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    parts (libavutil, libavcodec, libavformat) you are changing. You need
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    to change the version integer.
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    Incrementing the first component means no backward compatibility to
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    previous versions (e.g. removal of a function from the public API).
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    Incrementing the second component means backward compatible change
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    (e.g. addition of a function to the public API or extension of an
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    existing data structure).
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    Incrementing the third component means a noteworthy binary compatible
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    change (e.g. encoder bug fix that matters for the decoder).
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@item
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    Compiler warnings indicate potential bugs or code with bad style.
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    If it is a bug, the bug has to be fixed. If it is not, the code should
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    be changed to not generate a warning unless that causes a slowdown
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    or obfuscates the code.
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    If a type of warning leads to too many false positives, that warning
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    should be disabled, not the code changed.
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@item
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    If you add a new file, give it a proper license header. Do not copy and
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    paste it from a random place, use an existing file as template.
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@end enumerate
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We think our rules are not too hard. If you have comments, contact us.
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Note, some rules were borrowed from the MPlayer project.
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@section Submitting patches
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First, read the (@pxref{Coding Rules}) above if you did not yet, in particular
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the rules regarding patch submission.
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As stated already, please do not submit a patch which contains several
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unrelated changes.
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Split it into separate, self-contained pieces. This does not mean splitting
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file by file. Instead, make the patch as small as possible while still
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keeping it as a logical unit that contains an individual change, even
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if it spans multiple files. This makes reviewing your patches much easier
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for us and greatly increases your chances of getting your patch applied.
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Use the patcheck tool of Libav to check your patch.
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The tool is located in the tools directory.
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Run the @pxref{Regression Tests} before submitting a patch in order to verify
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it does not cause unexpected problems.
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Patches should be posted as base64 encoded attachments (or any other
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encoding which ensures that the patch will not be trashed during
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transmission) to the libav-devel mailing list, see
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@url{https://lists.libav.org/mailman/listinfo/libav-devel}
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It also helps quite a bit if you tell us what the patch does (for example
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'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
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and has no lrint()'). This kind of explanation should be the body of the
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commit message.
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Also please if you send several patches, send each patch as a separate mail,
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do not attach several unrelated patches to the same mail.
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Use @code{git send-email} when possible since it will properly send patches
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without requiring extra care.
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Your patch will be reviewed on the mailing list. You will likely be asked
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to make some changes and are expected to send in an improved version that
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incorporates the requests from the review. This process may go through
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several iterations. Once your patch is deemed good enough, it will be
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committed to the official Libav tree.
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Give us a few days to react. But if some time passes without reaction,
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send a reminder by email. Your patch should eventually be dealt with.
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@section New codecs or formats checklist
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@enumerate
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@item
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    Did you use av_cold for codec initialization and close functions?
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@item
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    Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
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    AVInputFormat/AVOutputFormat struct?
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@item
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    Did you bump the minor version number (and reset the micro version
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    number) in @file{avcodec.h} or @file{avformat.h}?
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@item
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    Did you register it in @file{allcodecs.c} or @file{allformats.c}?
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@item
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    Did you add the CodecID to @file{avcodec.h}?
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@item
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    If it has a fourcc, did you add it to @file{libavformat/riff.c},
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    even if it is only a decoder?
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@item
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    Did you add a rule to compile the appropriate files in the Makefile?
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    Remember to do this even if you are just adding a format to a file that
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    is already being compiled by some other rule, like a raw demuxer.
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@item
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    Did you add an entry to the table of supported formats or codecs in
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    @file{doc/general.texi}?
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@item
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    Did you add an entry in the Changelog?
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@item
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    If it depends on a parser or a library, did you add that dependency in
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    configure?
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@item
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    Did you @code{git add} the appropriate files before committing?
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@end enumerate
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@section patch submission checklist
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@enumerate
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@item
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    Do the regression tests pass with the patch applied?
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@item
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    Does @code{make checkheaders} pass with the patch applied?
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@item
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    Is the patch against latest Libav git master branch?
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@item
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    Are you subscribed to libav-devel?
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    (@url{https://lists.libav.org/mailman/listinfo/libav-devel}
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     the list is subscribers)
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@item
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    Have you checked that the changes are minimal, so that the same cannot be
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    achieved with a smaller patch and/or simpler final code?
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@item
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    If the change is to speed critical code, did you benchmark it?
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@item
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    If you did any benchmarks, did you provide them in the mail?
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@item
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    Have you checked that the patch does not introduce buffer overflows or
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    other security issues?
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@item
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    Did you test your decoder or demuxer against damaged data? If no, see
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    tools/trasher and the noise bitstream filter. Your decoder or demuxer
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    should not crash or end in a (near) infinite loop when fed damaged data.
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@item
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    Does the patch not mix functional and cosmetic changes?
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@item
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    Did you add tabs or trailing whitespace to the code? Both are forbidden.
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@item
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    Is the patch attached to the email you send?
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@item
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    Is the mime type of the patch correct? It should be text/x-diff or
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    text/x-patch or at least text/plain and not application/octet-stream.
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@item
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    If the patch fixes a bug, did you provide a verbose analysis of the bug?
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@item
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    If the patch fixes a bug, did you provide enough information, including
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    a sample, so the bug can be reproduced and the fix can be verified?
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    Note please do not attach samples >100k to mails but rather provide a
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    URL, you can upload to ftp://upload.libav.org
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@item
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    Did you provide a verbose summary about what the patch does change?
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@item
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    Did you provide a verbose explanation why it changes things like it does?
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@item
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    Did you provide a verbose summary of the user visible advantages and
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    disadvantages if the patch is applied?
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@item
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    Did you provide an example so we can verify the new feature added by the
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    patch easily?
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@item
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    If you added a new file, did you insert a license header? It should be
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    taken from Libav, not randomly copied and pasted from somewhere else.
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@item
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    You should maintain alphabetical order in alphabetically ordered lists as
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    long as doing so does not break API/ABI compatibility.
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@item
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    Lines with similar content should be aligned vertically when doing so
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    improves readability.
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@end enumerate
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@section Patch review process
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All patches posted to libav-devel will be reviewed, unless they contain a
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clear note that the patch is not for the git master branch.
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Reviews and comments will be posted as replies to the patch on the
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mailing list. The patch submitter then has to take care of every comment,
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that can be by resubmitting a changed patch or by discussion. Resubmitted
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patches will themselves be reviewed like any other patch. If at some point
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a patch passes review with no comments then it is approved, that can for
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simple and small patches happen immediately while large patches will generally
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have to be changed and reviewed many times before they are approved.
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After a patch is approved it will be committed to the repository.
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We will review all submitted patches, but sometimes we are quite busy so
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especially for large patches this can take several weeks.
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When resubmitting patches, if their size grew or during the review different
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issues arisen please split the patch so each issue has a specific patch.
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@anchor{Regression Tests}
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@section Regression Tests
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Before submitting a patch (or committing to the repository), you should at
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least make sure that it does not break anything.
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If the code changed has already a test present in FATE you should run it,
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otherwise it is advised to add it.
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Improvements to codec or demuxer might change the FATE results. Make sure
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to commit the update reference with the change and to explain in the comment
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why the expected result changed.
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Please refer to @file{doc/fate.txt}.
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@bye