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 should be composed with underscores (_), not CamelCase. For example,
151 @samp{avfilter_get_video_buffer} is an acceptable function name and
152 @samp{AVFilterGetVideo} is not. The exception from this are type names, like
153 for example structs and enums; they should always be in the CamelCase
155 There are the following conventions for naming variables and functions:
158 For local variables no prefix is required.
160 For file-scope variables and functions declared as @code{static}, no prefix
163 For variables and functions visible outside of file scope, but only used
164 internally by a library, an @code{ff_} prefix should be used,
165 e.g. @samp{ff_w64_demuxer}.
167 For variables and functions visible outside of file scope, used internally
168 across multiple libraries, use @code{avpriv_} as prefix, for example,
169 @samp{avpriv_aac_parse_header}.
171 Each library has its own prefix for public symbols, in addition to the
172 commonly used @code{av_} (@code{avformat_} for libavformat,
173 @code{avcodec_} for libavcodec, @code{swr_} for libswresample, etc).
174 Check the existing code and choose names accordingly.
175 Note that some symbols without these prefixes are also exported for
176 retro-compatibility reasons. These exceptions are declared in the
177 @code{lib<name>/lib<name>.v} files.
180 Furthermore, name space reserved for the system should not be invaded.
181 Identifiers ending in @code{_t} are reserved by
182 @url{http://pubs.opengroup.org/onlinepubs/007904975/functions/xsh_chap02_02.html#tag_02_02_02, POSIX}.
183 Also avoid names starting with @code{__} or @code{_} followed by an uppercase
184 letter as they are reserved by the C standard. Names starting with @code{_}
185 are reserved at the file level and may not be used for externally visible
186 symbols. If in doubt, just avoid names starting with @code{_} altogether.
188 @subsection Miscellaneous conventions
191 fprintf and printf are forbidden in libavformat and libavcodec,
192 please use av_log() instead.
194 Casts should be used only when necessary. Unneeded parentheses
195 should also be avoided if they don't make the code easier to understand.
198 @subsection Editor configuration
199 In order to configure Vim to follow FFmpeg formatting conventions, paste
200 the following snippet into your @file{.vimrc}:
202 " indentation rules for FFmpeg: 4 spaces, no tabs
208 " Allow tabs in Makefiles.
209 autocmd FileType make,automake set noexpandtab shiftwidth=8 softtabstop=8
210 " Trailing whitespace and tabs are forbidden, so highlight them.
211 highlight ForbiddenWhitespace ctermbg=red guibg=red
212 match ForbiddenWhitespace /\s\+$\|\t/
213 " Do not highlight spaces at the end of line while typing on that line.
214 autocmd InsertEnter * match ForbiddenWhitespace /\t\|\s\+\%#\@@<!$/
217 For Emacs, add these roughly equivalent lines to your @file{.emacs.d/init.el}:
219 (c-add-style "ffmpeg"
222 (indent-tabs-mode . nil)
223 (show-trailing-whitespace . t)
225 (statement-cont . (c-lineup-assignments +)))
228 (setq c-default-style "ffmpeg")
231 @section Development Policy
235 Contributions should be licensed under the
236 @uref{http://www.gnu.org/licenses/lgpl-2.1.html, LGPL 2.1},
237 including an "or any later version" clause, or, if you prefer
238 a gift-style license, the
239 @uref{http://www.isc.org/software/license/, ISC} or
240 @uref{http://mit-license.org/, MIT} license.
241 @uref{http://www.gnu.org/licenses/gpl-2.0.html, GPL 2} including
242 an "or any later version" clause is also acceptable, but LGPL is
245 You must not commit code which breaks FFmpeg! (Meaning unfinished but
246 enabled code which breaks compilation or compiles but does not work or
247 breaks the regression tests)
248 You can commit unfinished stuff (for testing etc), but it must be disabled
249 (#ifdef etc) by default so it does not interfere with other developers'
252 The commit message should have a short first line in the form of
253 a @samp{topic: short description} as a header, separated by a newline
254 from the body consisting of an explanation of why the change is necessary.
255 If the commit fixes a known bug on the bug tracker, the commit message
256 should include its bug ID. Referring to the issue on the bug tracker does
257 not exempt you from writing an excerpt of the bug in the commit message.
259 You do not have to over-test things. If it works for you, and you think it
260 should work for others, then commit. If your code has problems
261 (portability, triggers compiler bugs, unusual environment etc) they will be
262 reported and eventually fixed.
264 Do not commit unrelated changes together, split them into self-contained
265 pieces. Also do not forget that if part B depends on part A, but A does not
266 depend on B, then A can and should be committed first and separate from B.
267 Keeping changes well split into self-contained parts makes reviewing and
268 understanding them on the commit log mailing list easier. This also helps
269 in case of debugging later on.
270 Also if you have doubts about splitting or not splitting, do not hesitate to
271 ask/discuss it on the developer mailing list.
273 Do not change behavior of the programs (renaming options etc) or public
274 API or ABI without first discussing it on the ffmpeg-devel mailing list.
275 Do not remove functionality from the code. Just improve!
277 Note: Redundant code can be removed.
279 Do not commit changes to the build system (Makefiles, configure script)
280 which change behavior, defaults etc, without asking first. The same
281 applies to compiler warning fixes, trivial looking fixes and to code
282 maintained by other developers. We usually have a reason for doing things
283 the way we do. Send your changes as patches to the ffmpeg-devel mailing
284 list, and if the code maintainers say OK, you may commit. This does not
285 apply to files you wrote and/or maintain.
287 We refuse source indentation and other cosmetic changes if they are mixed
288 with functional changes, such commits will be rejected and removed. Every
289 developer has his own indentation style, you should not change it. Of course
290 if you (re)write something, you can use your own style, even though we would
291 prefer if the indentation throughout FFmpeg was consistent (Many projects
292 force a given indentation style - we do not.). If you really need to make
293 indentation changes (try to avoid this), separate them strictly from real
296 NOTE: If you had to put if()@{ .. @} over a large (> 5 lines) chunk of code,
297 then either do NOT change the indentation of the inner part within (do not
298 move it to the right)! or do so in a separate commit
300 Always fill out the commit log message. Describe in a few lines what you
301 changed and why. You can refer to mailing list postings if you fix a
302 particular bug. Comments such as "fixed!" or "Changed it." are unacceptable.
304 area changed: Short 1 line description
306 details describing what and why and giving references.
308 Make sure the author of the commit is set correctly. (see git commit --author)
309 If you apply a patch, send an
310 answer to ffmpeg-devel (or wherever you got the patch from) saying that
311 you applied the patch.
313 When applying patches that have been discussed (at length) on the mailing
314 list, reference the thread in the log message.
316 Do NOT commit to code actively maintained by others without permission.
317 Send a patch to ffmpeg-devel instead. If no one answers within a reasonable
318 timeframe (12h for build failures and security fixes, 3 days small changes,
319 1 week for big patches) then commit your patch if you think it is OK.
320 Also note, the maintainer can simply ask for more time to review!
322 Subscribe to the ffmpeg-cvslog mailing list. The diffs of all commits
323 are sent there and reviewed by all the other developers. Bugs and possible
324 improvements or general questions regarding commits are discussed there. We
325 expect you to react if problems with your code are uncovered.
327 Update the documentation if you change behavior or add features. If you are
328 unsure how best to do this, send a patch to ffmpeg-devel, the documentation
329 maintainer(s) will review and commit your stuff.
331 Try to keep important discussions and requests (also) on the public
332 developer mailing list, so that all developers can benefit from them.
334 Never write to unallocated memory, never write over the end of arrays,
335 always check values read from some untrusted source before using them
336 as array index or other risky things.
338 Remember to check if you need to bump versions for the specific libav*
339 parts (libavutil, libavcodec, libavformat) you are changing. You need
340 to change the version integer.
341 Incrementing the first component means no backward compatibility to
342 previous versions (e.g. removal of a function from the public API).
343 Incrementing the second component means backward compatible change
344 (e.g. addition of a function to the public API or extension of an
345 existing data structure).
346 Incrementing the third component means a noteworthy binary compatible
347 change (e.g. encoder bug fix that matters for the decoder). The third
348 component always starts at 100 to distinguish FFmpeg from Libav.
350 Compiler warnings indicate potential bugs or code with bad style. If a type of
351 warning always points to correct and clean code, that warning should
352 be disabled, not the code changed.
353 Thus the remaining warnings can either be bugs or correct code.
354 If it is a bug, the bug has to be fixed. If it is not, the code should
355 be changed to not generate a warning unless that causes a slowdown
356 or obfuscates the code.
358 If you add a new file, give it a proper license header. Do not copy and
359 paste it from a random place, use an existing file as template.
362 We think our rules are not too hard. If you have comments, contact us.
364 @anchor{Submitting patches}
365 @section Submitting patches
367 First, read the @ref{Coding Rules} above if you did not yet, in particular
368 the rules regarding patch submission.
370 When you submit your patch, please use @code{git format-patch} or
371 @code{git send-email}. We cannot read other diffs :-)
373 Also please do not submit a patch which contains several unrelated changes.
374 Split it into separate, self-contained pieces. This does not mean splitting
375 file by file. Instead, make the patch as small as possible while still
376 keeping it as a logical unit that contains an individual change, even
377 if it spans multiple files. This makes reviewing your patches much easier
378 for us and greatly increases your chances of getting your patch applied.
380 Use the patcheck tool of FFmpeg to check your patch.
381 The tool is located in the tools directory.
383 Run the @ref{Regression tests} before submitting a patch in order to verify
384 it does not cause unexpected problems.
386 It also helps quite a bit if you tell us what the patch does (for example
387 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
390 Also please if you send several patches, send each patch as a separate mail,
391 do not attach several unrelated patches to the same mail.
393 Patches should be posted to the
394 @uref{http://lists.ffmpeg.org/mailman/listinfo/ffmpeg-devel, ffmpeg-devel}
395 mailing list. Use @code{git send-email} when possible since it will properly
396 send patches without requiring extra care. If you cannot, then send patches
397 as base64-encoded attachments, so your patch is not trashed during
400 Your patch will be reviewed on the mailing list. You will likely be asked
401 to make some changes and are expected to send in an improved version that
402 incorporates the requests from the review. This process may go through
403 several iterations. Once your patch is deemed good enough, some developer
404 will pick it up and commit it to the official FFmpeg tree.
406 Give us a few days to react. But if some time passes without reaction,
407 send a reminder by email. Your patch should eventually be dealt with.
410 @section New codecs or formats checklist
414 Did you use av_cold for codec initialization and close functions?
416 Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
417 AVInputFormat/AVOutputFormat struct?
419 Did you bump the minor version number (and reset the micro version
420 number) in @file{libavcodec/version.h} or @file{libavformat/version.h}?
422 Did you register it in @file{allcodecs.c} or @file{allformats.c}?
424 Did you add the AVCodecID to @file{avcodec.h}?
425 When adding new codec IDs, also add an entry to the codec descriptor
426 list in @file{libavcodec/codec_desc.c}.
428 If it has a FourCC, did you add it to @file{libavformat/riff.c},
429 even if it is only a decoder?
431 Did you add a rule to compile the appropriate files in the Makefile?
432 Remember to do this even if you're just adding a format to a file that is
433 already being compiled by some other rule, like a raw demuxer.
435 Did you add an entry to the table of supported formats or codecs in
436 @file{doc/general.texi}?
438 Did you add an entry in the Changelog?
440 If it depends on a parser or a library, did you add that dependency in
443 Did you @code{git add} the appropriate files before committing?
445 Did you make sure it compiles standalone, i.e. with
446 @code{configure --disable-everything --enable-decoder=foo}
447 (or @code{--enable-demuxer} or whatever your component is)?
451 @section patch submission checklist
455 Does @code{make fate} pass with the patch applied?
457 Was the patch generated with git format-patch or send-email?
459 Did you sign off your patch? (git commit -s)
460 See @url{http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=blob_plain;f=Documentation/SubmittingPatches} for the meaning
463 Did you provide a clear git commit log message?
465 Is the patch against latest FFmpeg git master branch?
467 Are you subscribed to ffmpeg-devel?
468 (the list is subscribers only due to spam)
470 Have you checked that the changes are minimal, so that the same cannot be
471 achieved with a smaller patch and/or simpler final code?
473 If the change is to speed critical code, did you benchmark it?
475 If you did any benchmarks, did you provide them in the mail?
477 Have you checked that the patch does not introduce buffer overflows or
478 other security issues?
480 Did you test your decoder or demuxer against damaged data? If no, see
481 tools/trasher, the noise bitstream filter, and
482 @uref{http://caca.zoy.org/wiki/zzuf, zzuf}. Your decoder or demuxer
483 should not crash, end in a (near) infinite loop, or allocate ridiculous
484 amounts of memory when fed damaged data.
486 Does the patch not mix functional and cosmetic changes?
488 Did you add tabs or trailing whitespace to the code? Both are forbidden.
490 Is the patch attached to the email you send?
492 Is the mime type of the patch correct? It should be text/x-diff or
493 text/x-patch or at least text/plain and not application/octet-stream.
495 If the patch fixes a bug, did you provide a verbose analysis of the bug?
497 If the patch fixes a bug, did you provide enough information, including
498 a sample, so the bug can be reproduced and the fix can be verified?
499 Note please do not attach samples >100k to mails but rather provide a
500 URL, you can upload to ftp://upload.ffmpeg.org
502 Did you provide a verbose summary about what the patch does change?
504 Did you provide a verbose explanation why it changes things like it does?
506 Did you provide a verbose summary of the user visible advantages and
507 disadvantages if the patch is applied?
509 Did you provide an example so we can verify the new feature added by the
512 If you added a new file, did you insert a license header? It should be
513 taken from FFmpeg, not randomly copied and pasted from somewhere else.
515 You should maintain alphabetical order in alphabetically ordered lists as
516 long as doing so does not break API/ABI compatibility.
518 Lines with similar content should be aligned vertically when doing so
519 improves readability.
521 Consider to add a regression test for your code.
523 If you added YASM code please check that things still work with --disable-yasm
525 Make sure you check the return values of function and return appropriate
526 error codes. Especially memory allocation functions like @code{av_malloc()}
527 are notoriously left unchecked, which is a serious problem.
529 Test your code with valgrind and or Address Sanitizer to ensure it's free
530 of leaks, out of array accesses, etc.
533 @section Patch review process
535 All patches posted to ffmpeg-devel will be reviewed, unless they contain a
536 clear note that the patch is not for the git master branch.
537 Reviews and comments will be posted as replies to the patch on the
538 mailing list. The patch submitter then has to take care of every comment,
539 that can be by resubmitting a changed patch or by discussion. Resubmitted
540 patches will themselves be reviewed like any other patch. If at some point
541 a patch passes review with no comments then it is approved, that can for
542 simple and small patches happen immediately while large patches will generally
543 have to be changed and reviewed many times before they are approved.
544 After a patch is approved it will be committed to the repository.
546 We will review all submitted patches, but sometimes we are quite busy so
547 especially for large patches this can take several weeks.
549 If you feel that the review process is too slow and you are willing to try to
550 take over maintainership of the area of code you change then just clone
551 git master and maintain the area of code there. We will merge each area from
552 where its best maintained.
554 When resubmitting patches, please do not make any significant changes
555 not related to the comments received during review. Such patches will
556 be rejected. Instead, submit significant changes or new features as
559 @anchor{Regression tests}
560 @section Regression tests
562 Before submitting a patch (or committing to the repository), you should at least
563 test that you did not break anything.
565 Running 'make fate' accomplishes this, please see @url{fate.html} for details.
567 [Of course, some patches may change the results of the regression tests. In
568 this case, the reference results of the regression tests shall be modified
571 @subsection Adding files to the fate-suite dataset
573 When there is no muxer or encoder available to generate test media for a
574 specific test then the media has to be inlcuded in the fate-suite.
575 First please make sure that the sample file is as small as possible to test the
576 respective decoder or demuxer sufficiently. Large files increase network
577 bandwidth and disk space requirements.
578 Once you have a working fate test and fate sample, provide in the commit
579 message or introductionary message for the patch series that you post to
580 the ffmpeg-devel mailing list, a direct link to download the sample media.
583 @subsection Visualizing Test Coverage
585 The FFmpeg build system allows visualizing the test coverage in an easy
586 manner with the coverage tools @code{gcov}/@code{lcov}. This involves
591 Configure to compile with instrumentation enabled:
592 @code{configure --toolchain=gcov}.
594 Run your test case, either manually or via FATE. This can be either
595 the full FATE regression suite, or any arbitrary invocation of any
596 front-end tool provided by FFmpeg, in any combination.
598 Run @code{make lcov} to generate coverage data in HTML format.
600 View @code{lcov/index.html} in your preferred HTML viewer.
603 You can use the command @code{make lcov-reset} to reset the coverage
604 measurements. You will need to rerun @code{make lcov} after running a
607 @subsection Using Valgrind
609 The configure script provides a shortcut for using valgrind to spot bugs
610 related to memory handling. Just add the option
611 @code{--toolchain=valgrind-memcheck} or @code{--toolchain=valgrind-massif}
612 to your configure line, and reasonable defaults will be set for running
613 FATE under the supervision of either the @strong{memcheck} or the
614 @strong{massif} tool of the valgrind suite.
616 In case you need finer control over how valgrind is invoked, use the
617 @code{--target-exec='valgrind <your_custom_valgrind_options>} option in
618 your configure line instead.
620 @anchor{Release process}
621 @section Release process
623 FFmpeg maintains a set of @strong{release branches}, which are the
624 recommended deliverable for system integrators and distributors (such as
625 Linux distributions, etc.). At regular times, a @strong{release
626 manager} prepares, tests and publishes tarballs on the
627 @url{http://ffmpeg.org} website.
629 There are two kinds of releases:
633 @strong{Major releases} always include the latest and greatest
634 features and functionality.
636 @strong{Point releases} are cut from @strong{release} branches,
637 which are named @code{release/X}, with @code{X} being the release
641 Note that we promise to our users that shared libraries from any FFmpeg
642 release never break programs that have been @strong{compiled} against
643 previous versions of @strong{the same release series} in any case!
645 However, from time to time, we do make API changes that require adaptations
646 in applications. Such changes are only allowed in (new) major releases and
647 require further steps such as bumping library version numbers and/or
648 adjustments to the symbol versioning file. Please discuss such changes
649 on the @strong{ffmpeg-devel} mailing list in time to allow forward planning.
651 @anchor{Criteria for Point Releases}
652 @subsection Criteria for Point Releases
654 Changes that match the following criteria are valid candidates for
655 inclusion into a point release:
659 Fixes a security issue, preferably identified by a @strong{CVE
660 number} issued by @url{http://cve.mitre.org/}.
662 Fixes a documented bug in @url{https://ffmpeg.org/trac/ffmpeg}.
664 Improves the included documentation.
666 Retains both source code and binary compatibility with previous
667 point releases of the same release branch.
670 The order for checking the rules is (1 OR 2 OR 3) AND 4.
673 @subsection Release Checklist
675 The release process involves the following steps:
679 Ensure that the @file{RELEASE} file contains the version number for
680 the upcoming release.
682 Add the release at @url{https://ffmpeg.org/trac/ffmpeg/admin/ticket/versions}.
684 Announce the intent to do a release to the mailing list.
686 Make sure all relevant security fixes have been backported. See
687 @url{https://ffmpeg.org/security.html}.
689 Ensure that the FATE regression suite still passes in the release
690 branch on at least @strong{i386} and @strong{amd64}
691 (cf. @ref{Regression tests}).
693 Prepare the release tarballs in @code{bz2} and @code{gz} formats, and
694 supplementing files that contain @code{gpg} signatures
696 Publish the tarballs at @url{http://ffmpeg.org/releases}. Create and
697 push an annotated tag in the form @code{nX}, with @code{X}
698 containing the version number.
700 Propose and send a patch to the @strong{ffmpeg-devel} mailing list
701 with a news entry for the website.
703 Publish the news entry.
705 Send announcement to the mailing list.