1 \input texinfo @c -*- texinfo -*-
3 @settitle Developer Documentation
5 @center @titlefont{Developer Documentation}
12 @chapter Developers Guide
16 @item libavcodec is the library containing the codecs (both encoding and
17 decoding). Look at @file{doc/examples/decoding_encoding.c} to see how to use
20 @item libavformat is the library containing the file format handling (mux and
21 demux code for several formats). Look at @file{ffplay.c} to use it in a
22 player. See @file{doc/examples/muxing.c} to use it to generate audio or video
27 @section Integrating libavcodec or libavformat in your program
29 You can integrate all the source code of the libraries to link them
30 statically to avoid any version problem. All you need is to provide a
31 'config.mak' and a 'config.h' in the parent directory. See the defines
32 generated by ./configure to understand what is needed.
34 You can use libavcodec or libavformat in your commercial program, but
35 @emph{any patch you make must be published}. The best way to proceed is
36 to send your patches to the FFmpeg mailing list.
40 There are 3 ways by which code gets into ffmpeg.
42 @item Submitting Patches to the main developer mailing list
43 see @ref{Submitting patches} for details.
44 @item Directly committing changes to the main tree.
45 @item Committing changes to a git clone, for example on github.com or
46 gitorious.org. And asking us to merge these changes.
49 Whichever way, changes should be reviewed by the maintainer of the code
50 before they are committed. And they should follow the @ref{Coding Rules}.
51 The developer making the commit and the author are responsible for their changes
52 and should try to fix issues their commit causes.
57 @subsection Code formatting conventions
59 There are the following guidelines regarding the indentation in files:
64 The TAB character is forbidden outside of Makefiles as is any
65 form of trailing whitespace. Commits containing either will be
66 rejected by the git repository.
68 You should try to limit your code lines to 80 characters; however, do so if
69 and only if this improves readability.
71 The presentation is one inspired by 'indent -i4 -kr -nut'.
73 The main priority in FFmpeg is simplicity and small code size in order to
74 minimize the bug count.
77 Use the JavaDoc/Doxygen format (see examples below) so that code documentation
78 can be generated automatically. All nontrivial functions should have a comment
79 above them explaining what the function does, even if it is just one sentence.
80 All structures and their member variables should be documented, too.
82 Avoid Qt-style and similar Doxygen syntax with @code{!} in it, i.e. replace
83 @code{//!} with @code{///} and similar. Also @@ syntax should be employed
84 for markup commands, i.e. use @code{@@param} and not @code{\param}.
98 typedef struct Foobar@{
99 int var1; /**< var1 description */
100 int var2; ///< var2 description
101 /** var3 description */
109 * @@param my_parameter description of my_parameter
110 * @@return return value description
112 int myfunc(int my_parameter)
116 @subsection C language features
118 FFmpeg is programmed in the ISO C90 language with a few additional
119 features from ISO C99, namely:
122 the @samp{inline} keyword;
126 designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
128 compound literals (@samp{x = (struct s) @{ 17, 23 @};})
131 These features are supported by all compilers we care about, so we will not
132 accept patches to remove their use unless they absolutely do not impair
133 clarity and performance.
135 All code must compile with recent versions of GCC and a number of other
136 currently supported compilers. To ensure compatibility, please do not use
137 additional C99 features or GCC extensions. Especially watch out for:
140 mixing statements and declarations;
142 @samp{long long} (use @samp{int64_t} instead);
144 @samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;
146 GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
149 @subsection Naming conventions
150 All names are using underscores (_), not CamelCase. For example, @samp{avfilter_get_video_buffer} is
151 a valid function name and @samp{AVFilterGetVideo} is not. The exception from this are type names, like
152 for example structs and enums; they should always be in the CamelCase
155 There are following conventions for naming variables and functions:
158 For local variables no prefix is required.
160 For variables and functions declared as @code{static} no prefixes are required.
162 For variables and functions used internally by the library, @code{ff_} prefix
164 For example, @samp{ff_w64_demuxer}.
166 For variables and functions used internally across multiple libraries, use
167 @code{avpriv_}. For example, @samp{avpriv_aac_parse_header}.
169 For exported names, each library has its own prefixes. Just check the existing
170 code and name accordingly.
173 @subsection Miscellanous conventions
176 fprintf and printf are forbidden in libavformat and libavcodec,
177 please use av_log() instead.
179 Casts should be used only when necessary. Unneeded parentheses
180 should also be avoided if they don't make the code easier to understand.
183 @subsection Editor configuration
184 In order to configure Vim to follow FFmpeg formatting conventions, paste
185 the following snippet into your @file{.vimrc}:
187 " indentation rules for FFmpeg: 4 spaces, no tabs
193 " allow tabs in Makefiles
194 autocmd FileType make set noexpandtab shiftwidth=8 softtabstop=8
195 " Trailing whitespace and tabs are forbidden, so highlight them.
196 highlight ForbiddenWhitespace ctermbg=red guibg=red
197 match ForbiddenWhitespace /\s\+$\|\t/
198 " Do not highlight spaces at the end of line while typing on that line.
199 autocmd InsertEnter * match ForbiddenWhitespace /\t\|\s\+\%#\@@<!$/
202 For Emacs, add these roughly equivalent lines to your @file{.emacs.d/init.el}:
204 (c-add-style "ffmpeg"
207 (indent-tabs-mode . nil)
208 (show-trailing-whitespace . t)
210 (statement-cont . (c-lineup-assignments +)))
213 (setq c-default-style "ffmpeg")
216 @section Development Policy
220 Contributions should be licensed under the LGPL 2.1, including an
221 "or any later version" clause, or the MIT license. GPL 2 including
222 an "or any later version" clause is also acceptable, but LGPL is
225 You must not commit code which breaks FFmpeg! (Meaning unfinished but
226 enabled code which breaks compilation or compiles but does not work or
227 breaks the regression tests)
228 You can commit unfinished stuff (for testing etc), but it must be disabled
229 (#ifdef etc) by default so it does not interfere with other developers'
232 You do not have to over-test things. If it works for you, and you think it
233 should work for others, then commit. If your code has problems
234 (portability, triggers compiler bugs, unusual environment etc) they will be
235 reported and eventually fixed.
237 Do not commit unrelated changes together, split them into self-contained
238 pieces. Also do not forget that if part B depends on part A, but A does not
239 depend on B, then A can and should be committed first and separate from B.
240 Keeping changes well split into self-contained parts makes reviewing and
241 understanding them on the commit log mailing list easier. This also helps
242 in case of debugging later on.
243 Also if you have doubts about splitting or not splitting, do not hesitate to
244 ask/discuss it on the developer mailing list.
246 Do not change behavior of the programs (renaming options etc) or public
247 API or ABI without first discussing it on the ffmpeg-devel mailing list.
248 Do not remove functionality from the code. Just improve!
250 Note: Redundant code can be removed.
252 Do not commit changes to the build system (Makefiles, configure script)
253 which change behavior, defaults etc, without asking first. The same
254 applies to compiler warning fixes, trivial looking fixes and to code
255 maintained by other developers. We usually have a reason for doing things
256 the way we do. Send your changes as patches to the ffmpeg-devel mailing
257 list, and if the code maintainers say OK, you may commit. This does not
258 apply to files you wrote and/or maintain.
260 We refuse source indentation and other cosmetic changes if they are mixed
261 with functional changes, such commits will be rejected and removed. Every
262 developer has his own indentation style, you should not change it. Of course
263 if you (re)write something, you can use your own style, even though we would
264 prefer if the indentation throughout FFmpeg was consistent (Many projects
265 force a given indentation style - we do not.). If you really need to make
266 indentation changes (try to avoid this), separate them strictly from real
269 NOTE: If you had to put if()@{ .. @} over a large (> 5 lines) chunk of code,
270 then either do NOT change the indentation of the inner part within (do not
271 move it to the right)! or do so in a separate commit
273 Always fill out the commit log message. Describe in a few lines what you
274 changed and why. You can refer to mailing list postings if you fix a
275 particular bug. Comments such as "fixed!" or "Changed it." are unacceptable.
277 area changed: Short 1 line description
279 details describing what and why and giving references.
281 Make sure the author of the commit is set correctly. (see git commit --author)
282 If you apply a patch, send an
283 answer to ffmpeg-devel (or wherever you got the patch from) saying that
284 you applied the patch.
286 When applying patches that have been discussed (at length) on the mailing
287 list, reference the thread in the log message.
289 Do NOT commit to code actively maintained by others without permission.
290 Send a patch to ffmpeg-devel instead. If no one answers within a reasonable
291 timeframe (12h for build failures and security fixes, 3 days small changes,
292 1 week for big patches) then commit your patch if you think it is OK.
293 Also note, the maintainer can simply ask for more time to review!
295 Subscribe to the ffmpeg-cvslog mailing list. The diffs of all commits
296 are sent there and reviewed by all the other developers. Bugs and possible
297 improvements or general questions regarding commits are discussed there. We
298 expect you to react if problems with your code are uncovered.
300 Update the documentation if you change behavior or add features. If you are
301 unsure how best to do this, send a patch to ffmpeg-devel, the documentation
302 maintainer(s) will review and commit your stuff.
304 Try to keep important discussions and requests (also) on the public
305 developer mailing list, so that all developers can benefit from them.
307 Never write to unallocated memory, never write over the end of arrays,
308 always check values read from some untrusted source before using them
309 as array index or other risky things.
311 Remember to check if you need to bump versions for the specific libav*
312 parts (libavutil, libavcodec, libavformat) you are changing. You need
313 to change the version integer.
314 Incrementing the first component means no backward compatibility to
315 previous versions (e.g. removal of a function from the public API).
316 Incrementing the second component means backward compatible change
317 (e.g. addition of a function to the public API or extension of an
318 existing data structure).
319 Incrementing the third component means a noteworthy binary compatible
320 change (e.g. encoder bug fix that matters for the decoder).
322 Compiler warnings indicate potential bugs or code with bad style. If a type of
323 warning always points to correct and clean code, that warning should
324 be disabled, not the code changed.
325 Thus the remaining warnings can either be bugs or correct code.
326 If it is a bug, the bug has to be fixed. If it is not, the code should
327 be changed to not generate a warning unless that causes a slowdown
328 or obfuscates the code.
330 If you add a new file, give it a proper license header. Do not copy and
331 paste it from a random place, use an existing file as template.
334 We think our rules are not too hard. If you have comments, contact us.
336 Note, these rules are mostly borrowed from the MPlayer project.
338 @anchor{Submitting patches}
339 @section Submitting patches
341 First, read the @ref{Coding Rules} above if you did not yet, in particular
342 the rules regarding patch submission.
344 When you submit your patch, please use @code{git format-patch} or
345 @code{git send-email}. We cannot read other diffs :-)
347 Also please do not submit a patch which contains several unrelated changes.
348 Split it into separate, self-contained pieces. This does not mean splitting
349 file by file. Instead, make the patch as small as possible while still
350 keeping it as a logical unit that contains an individual change, even
351 if it spans multiple files. This makes reviewing your patches much easier
352 for us and greatly increases your chances of getting your patch applied.
354 Use the patcheck tool of FFmpeg to check your patch.
355 The tool is located in the tools directory.
357 Run the @ref{Regression tests} before submitting a patch in order to verify
358 it does not cause unexpected problems.
360 Patches should be posted as base64 encoded attachments (or any other
361 encoding which ensures that the patch will not be trashed during
362 transmission) to the ffmpeg-devel mailing list, see
363 @url{http://lists.ffmpeg.org/mailman/listinfo/ffmpeg-devel}
365 It also helps quite a bit if you tell us what the patch does (for example
366 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
369 Also please if you send several patches, send each patch as a separate mail,
370 do not attach several unrelated patches to the same mail.
372 Your patch will be reviewed on the mailing list. You will likely be asked
373 to make some changes and are expected to send in an improved version that
374 incorporates the requests from the review. This process may go through
375 several iterations. Once your patch is deemed good enough, some developer
376 will pick it up and commit it to the official FFmpeg tree.
378 Give us a few days to react. But if some time passes without reaction,
379 send a reminder by email. Your patch should eventually be dealt with.
382 @section New codecs or formats checklist
386 Did you use av_cold for codec initialization and close functions?
388 Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
389 AVInputFormat/AVOutputFormat struct?
391 Did you bump the minor version number (and reset the micro version
392 number) in @file{libavcodec/version.h} or @file{libavformat/version.h}?
394 Did you register it in @file{allcodecs.c} or @file{allformats.c}?
396 Did you add the AVCodecID to @file{avcodec.h}?
397 When adding new codec IDs, also add an entry to the codec descriptor
398 list in @file{libavcodec/codec_desc.c}.
400 If it has a fourCC, did you add it to @file{libavformat/riff.c},
401 even if it is only a decoder?
403 Did you add a rule to compile the appropriate files in the Makefile?
404 Remember to do this even if you're just adding a format to a file that is
405 already being compiled by some other rule, like a raw demuxer.
407 Did you add an entry to the table of supported formats or codecs in
408 @file{doc/general.texi}?
410 Did you add an entry in the Changelog?
412 If it depends on a parser or a library, did you add that dependency in
415 Did you @code{git add} the appropriate files before committing?
417 Did you make sure it compiles standalone, i.e. with
418 @code{configure --disable-everything --enable-decoder=foo}
419 (or @code{--enable-demuxer} or whatever your component is)?
423 @section patch submission checklist
427 Does @code{make fate} pass with the patch applied?
429 Was the patch generated with git format-patch or send-email?
431 Did you sign off your patch? (git commit -s)
432 See @url{http://kerneltrap.org/files/Jeremy/DCO.txt} for the meaning
435 Did you provide a clear git commit log message?
437 Is the patch against latest FFmpeg git master branch?
439 Are you subscribed to ffmpeg-devel?
440 (the list is subscribers only due to spam)
442 Have you checked that the changes are minimal, so that the same cannot be
443 achieved with a smaller patch and/or simpler final code?
445 If the change is to speed critical code, did you benchmark it?
447 If you did any benchmarks, did you provide them in the mail?
449 Have you checked that the patch does not introduce buffer overflows or
450 other security issues?
452 Did you test your decoder or demuxer against damaged data? If no, see
453 tools/trasher and the noise bitstream filter. Your decoder or demuxer
454 should not crash or end in a (near) infinite loop when fed damaged data.
456 Does the patch not mix functional and cosmetic changes?
458 Did you add tabs or trailing whitespace to the code? Both are forbidden.
460 Is the patch attached to the email you send?
462 Is the mime type of the patch correct? It should be text/x-diff or
463 text/x-patch or at least text/plain and not application/octet-stream.
465 If the patch fixes a bug, did you provide a verbose analysis of the bug?
467 If the patch fixes a bug, did you provide enough information, including
468 a sample, so the bug can be reproduced and the fix can be verified?
469 Note please do not attach samples >100k to mails but rather provide a
470 URL, you can upload to ftp://upload.ffmpeg.org
472 Did you provide a verbose summary about what the patch does change?
474 Did you provide a verbose explanation why it changes things like it does?
476 Did you provide a verbose summary of the user visible advantages and
477 disadvantages if the patch is applied?
479 Did you provide an example so we can verify the new feature added by the
482 If you added a new file, did you insert a license header? It should be
483 taken from FFmpeg, not randomly copied and pasted from somewhere else.
485 You should maintain alphabetical order in alphabetically ordered lists as
486 long as doing so does not break API/ABI compatibility.
488 Lines with similar content should be aligned vertically when doing so
489 improves readability.
491 Consider to add a regression test for your code.
493 If you added YASM code please check that things still work with --disable-yasm
495 Make sure you check the return values of function and return appropriate
496 error codes. Especially memory allocation functions like @code{av_malloc()}
497 are notoriously left unchecked, which is a serious problem.
500 @section Patch review process
502 All patches posted to ffmpeg-devel will be reviewed, unless they contain a
503 clear note that the patch is not for the git master branch.
504 Reviews and comments will be posted as replies to the patch on the
505 mailing list. The patch submitter then has to take care of every comment,
506 that can be by resubmitting a changed patch or by discussion. Resubmitted
507 patches will themselves be reviewed like any other patch. If at some point
508 a patch passes review with no comments then it is approved, that can for
509 simple and small patches happen immediately while large patches will generally
510 have to be changed and reviewed many times before they are approved.
511 After a patch is approved it will be committed to the repository.
513 We will review all submitted patches, but sometimes we are quite busy so
514 especially for large patches this can take several weeks.
516 If you feel that the review process is too slow and you are willing to try to
517 take over maintainership of the area of code you change then just clone
518 git master and maintain the area of code there. We will merge each area from
519 where its best maintained.
521 When resubmitting patches, please do not make any significant changes
522 not related to the comments received during review. Such patches will
523 be rejected. Instead, submit significant changes or new features as
526 @anchor{Regression tests}
527 @section Regression tests
529 Before submitting a patch (or committing to the repository), you should at least
530 test that you did not break anything.
532 Running 'make fate' accomplishes this, please see @url{fate.html} for details.
534 [Of course, some patches may change the results of the regression tests. In
535 this case, the reference results of the regression tests shall be modified
538 @subsection Adding files to the fate-suite dataset
540 When there is no muxer or encoder available to generate test media for a
541 specific test then the media has to be inlcuded in the fate-suite.
542 First please make sure that the sample file is as small as possible to test the
543 respective decoder or demuxer sufficiently. Large files increase network
544 bandwidth and disk space requirements.
545 Once you have a working fate test and fate sample, provide in the commit
546 message or introductionary message for the patch series that you post to
547 the ffmpeg-devel mailing list, a direct link to download the sample media.