mirror of https://github.com/FFmpeg/FFmpeg.git
Originally committed as revision 19269 to svn://svn.ffmpeg.org/ffmpeg/trunkrelease/0.6
Diego Biurrun
16 years ago
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\input texinfo @c -*- texinfo -*- |
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|
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@settitle Developer Documentation |
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@titlepage |
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@sp 7 |
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@center @titlefont{Developer Documentation} |
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@sp 3 |
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@end titlepage |
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|
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|
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@chapter Developers Guide |
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|
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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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|
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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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|
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@end itemize |
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|
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@section Integrating libavcodec or libavformat in your program |
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You can integrate all the source code of the libraries to link them |
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statically to avoid any version problem. All you need is to provide a |
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'config.mak' and a 'config.h' in the parent directory. See the defines |
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generated by ./configure to understand what is needed. |
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|
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You can use libavcodec or libavformat in your commercial program, but |
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@emph{any patch you make must be published}. The best way to proceed is |
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to send your patches to the FFmpeg mailing list. |
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|
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@node Coding Rules |
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@section Coding Rules |
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|
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FFmpeg 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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|
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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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|
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All code must compile with GCC 2.95 and GCC 3.3. Currently, FFmpeg 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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|
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Indent size is 4. |
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The presentation is the one specified 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 Subversion repository. |
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|
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The main priority in FFmpeg is simplicity and small code size in order to |
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minimize the bug count. |
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|
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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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/** |
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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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/** |
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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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|
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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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|
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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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|
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@section Development Policy |
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|
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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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You must not commit code which breaks FFmpeg! (Meaning unfinished but |
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enabled code which breaks compilation or compiles but does not work or |
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breaks the regression tests) |
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You can commit unfinished stuff (for testing etc), but it must be disabled |
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(#ifdef etc) by default so it does not interfere with other developers' |
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work. |
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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, then commit. If your code has problems |
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(portability, triggers compiler bugs, unusual environment etc) they will be |
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reported and eventually fixed. |
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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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Also if you have doubts about splitting or not splitting, do not hesitate to |
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ask/discuss it on the developer mailing list. |
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@item |
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Do not change behavior of the program (renaming options etc) without |
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first discussing it on the ffmpeg-devel mailing list. Do not remove |
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functionality from the code. Just improve! |
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|
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Note: Redundant code can be removed. |
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@item |
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Do not commit changes to the build system (Makefiles, configure script) |
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which change behavior, defaults etc, without asking first. The same |
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applies to compiler warning fixes, trivial looking fixes and to code |
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maintained by other developers. We usually have a reason for doing things |
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the way we do. Send your changes as patches to the ffmpeg-devel mailing |
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list, and if the code maintainers say OK, you may commit. This does not |
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apply to files you wrote and/or maintain. |
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@item |
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We refuse source indentation and other cosmetic changes if they are mixed |
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with functional changes, such commits will be rejected and removed. Every |
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developer has his own indentation style, you should not change it. Of course |
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if you (re)write something, you can use your own style, even though we would |
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prefer if the indentation throughout FFmpeg was consistent (Many projects |
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force a given indentation style - we do not.). If you really need to make |
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indentation changes (try to avoid this), separate them strictly from real |
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changes. |
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|
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NOTE: If you had to put if()@{ .. @} over a large (> 5 lines) chunk of code, |
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then either do NOT change the indentation of the inner part within (do not |
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move it to the right)! or do so in a separate commit |
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@item |
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Always fill out the commit log message. Describe in a few lines what you |
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changed and why. You can refer to mailing list postings if you fix a |
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particular bug. Comments such as "fixed!" or "Changed it." are unacceptable. |
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@item |
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If you apply a patch by someone else, include the name and email address in |
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the log message. Since the ffmpeg-cvslog mailing list is publicly |
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archived you should add some SPAM protection to the email address. Send an |
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answer to ffmpeg-devel (or wherever you got the patch from) saying that |
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you applied the patch. |
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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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Do NOT commit to code actively maintained by others without permission. |
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Send a patch to ffmpeg-devel instead. If no one answers within a reasonable |
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timeframe (12h for build failures and security fixes, 3 days small changes, |
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1 week for big patches) then commit your patch if you think it is OK. |
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Also note, the maintainer can simply ask for more time to review! |
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@item |
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Subscribe to the ffmpeg-cvslog mailing list. The diffs of all commits |
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are sent there and reviewed by all the other developers. Bugs and possible |
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improvements or general questions regarding commits are discussed there. We |
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expect you to react if problems with 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 a patch to ffmpeg-devel, the documentation |
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maintainer(s) will review and commit your stuff. |
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@item |
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Try to keep important discussions and requests (also) on the public |
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developer mailing list, so that all developers can benefit from them. |
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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. |
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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. If a type of |
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warning always points to correct and clean code, that warning should |
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be disabled, not the code changed. |
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Thus the remaining warnings can either be bugs or correct code. |
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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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@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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|
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We think our rules are not too hard. If you have comments, contact us. |
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Note, these rules are mostly borrowed from the MPlayer project. |
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@section Submitting patches |
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|
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First, (@pxref{Coding Rules}) above if you did not yet. |
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When you submit your patch, try to send a unified diff (diff '-up' |
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option). We cannot read other diffs :-) |
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|
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Also please do not submit a patch which contains several 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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|
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Run the regression tests before submitting a patch so that you can |
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verify that there are no big problems. |
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|
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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 ffmpeg-devel mailing list, see |
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@url{http://lists.mplayerhq.hu/mailman/listinfo/ffmpeg-devel} |
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|
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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()') |
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|
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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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|
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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 in @file{avcodec.h} or |
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@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're just adding a format to a file that is |
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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 the |
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documentation? |
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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 "svn add" the appropriate files before commiting? |
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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 a unified diff? |
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@item |
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Is the patch against latest FFmpeg SVN? |
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@item |
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Are you subscribed to ffmpeg-dev? |
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(the list is subscribers only due to spam) |
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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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Is the patch created from the root of the source tree, so it can be |
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applied with @code{patch -p0}? |
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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.ffmpeg.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 FFmpeg, 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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@item |
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Did you provide a suggestion for a clear commit log message? |
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@end enumerate |
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|
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@section Patch review process |
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|
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All patches posted to ffmpeg-devel will be reviewed, unless they contain a |
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clear note that the patch is not for SVN. |
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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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|
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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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|
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When resubmitting patches, please do not make any significant changes |
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not related to the comments received during review. Such patches will |
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be rejected. Instead, submit significant changes or new features as |
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separate patches. |
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|
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@section Regression tests |
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|
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Before submitting a patch (or committing to the repository), you should at least |
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test that you did not break anything. |
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|
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The regression tests build a synthetic video stream and a synthetic |
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audio stream. These are then encoded and decoded with all codecs or |
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formats. The CRC (or MD5) of each generated file is recorded in a |
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result file. A 'diff' is launched to compare the reference results and |
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the result file. |
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|
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The regression tests then go on to test the FFserver code with a |
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limited set of streams. It is important that this step runs correctly |
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as well. |
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Run 'make test' to test all the codecs and formats. |
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|
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Run 'make fulltest' to test all the codecs, formats and FFserver. |
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|
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[Of course, some patches may change the results of the regression tests. In |
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this case, the reference results of the regression tests shall be modified |
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accordingly]. |
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|
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@bye |
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