| \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 recent versions of GCC and a number of other |
| currently supported compilers. To ensure compatibility, please do not use |
| 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. |
| Recommanded format: |
| area changed: Short 1 line description |
| |
| details describing what and why and giving references. |
| @item |
| Make sure the author of the commit is set correctly. (see git commit --author) |
| If you apply a patch, 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, read the (@pxref{Coding Rules}) above if you did not yet. |
| |
| When you submit your patch, please use @code{git format-patch} or |
| @code{git send-email}. 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 @code{git add} the appropriate files before committing? |
| @item |
| Did you make sure it compiles standalone, i.e. with |
| @code{configure --disable-everything --enable-decoder=foo} |
| (or @code{--enable-demuxer} or whatever your component is)? |
| @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. |
| @item |
| Consider to add a regression test for your code. |
| @item |
| If you added YASM code please check that things still work with --disable-yasm |
| @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 |