1 \input texinfo @c -*- texinfo -*-
3 @settitle Developer Documentation
5 @center @titlefont{Developer Documentation}
12 @chapter Developers Guide
17 @item libavcodec is the library containing the codecs (both encoding and
18 decoding). Look at @file{libavcodec/apiexample.c} to see how to use it.
20 @item libavformat is the library containing the file format handling (mux and
21 demux code for several formats). Look at @file{avplay.c} to use it in a
22 player. See @file{libavformat/output-example.c} to use it to generate
23 audio or video streams.
26 @section Integrating libav in your program
28 Shared libraries should be used whenever is possible in order to reduce
29 the effort distributors have to pour to support programs and to ensure
30 only the public API is used.
32 You can use Libav in your commercial program, but you must abide to the
33 license, LGPL or GPL depending on the specific features used, please refer
34 to @uref{http://libav.org/legal.html, our legal page} for a quick checklist and to
35 the following links for the exact text of each license:
36 @uref{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.GPLv2, GPL version 2},
37 @uref{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.GPLv3, GPL version 3},
38 @uref{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.LGPLv2.1, LGPL version 2.1},
39 @uref{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.LGPLv3, LGPL version 3}.
40 Any modification to the source code can be suggested for inclusion.
41 The best way to proceed is to send your patches to the
42 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
48 @subsection Code formatting conventions
49 The code is written in K&R C style. That means the following:
53 The control statements are formatted by putting space between the statement
54 and parenthesis in the following way:
56 for (i = 0; i < filter->input_count; i++) @{
60 The case statement is always located at the same level as the switch itself:
62 switch (link->init_state) @{
65 case AVLINK_STARTINIT:
66 av_log(filter, AV_LOG_INFO, "circular filter chain detected");
71 Braces in function declarations are written on the new line:
73 const char *avfilter_configuration(void)
75 return LIBAV_CONFIGURATION;
80 Do not check for NULL values by comparison, @samp{if (p)} and
81 @samp{if (!p)} are correct; @samp{if (p == NULL)} and @samp{if (p != NULL)}
85 In case of a single-statement if, no curly braces are required:
92 Do not put spaces immediately inside parentheses. @samp{if (ret)} is
93 a valid style; @samp{if ( ret )} is not.
96 There are the following guidelines regarding the indentation in files:
103 The TAB character is forbidden outside of Makefiles as is any
104 form of trailing whitespace. Commits containing either will be
105 rejected by the git repository.
108 You should try to limit your code lines to 80 characters; however, do so if
109 and only if this improves readability.
111 The presentation is one inspired by 'indent -i4 -kr -nut'.
113 The main priority in Libav is simplicity and small code size in order to
114 minimize the bug count.
117 Use the JavaDoc/Doxygen format (see examples below) so that code documentation
118 can be generated automatically. All nontrivial functions should have a comment
119 above them explaining what the function does, even if it is just one sentence.
120 All structures and their member variables should be documented, too.
122 Avoid Qt-style and similar Doxygen syntax with @code{!} in it, i.e. replace
123 @code{//!} with @code{///} and similar. Also @@ syntax should be employed
124 for markup commands, i.e. use @code{@@param} and not @code{\param}.
138 typedef struct Foobar @{
139 int var1; /**< var1 description */
140 int var2; ///< var2 description
141 /** var3 description */
149 * @@param my_parameter description of my_parameter
150 * @@return return value description
152 int myfunc(int my_parameter)
156 @subsection C language features
158 Libav is programmed in the ISO C90 language with a few additional
159 features from ISO C99, namely:
163 the @samp{inline} keyword;
169 designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
172 compound literals (@samp{x = (struct s) @{ 17, 23 @};})
175 These features are supported by all compilers we care about, so we will not
176 accept patches to remove their use unless they absolutely do not impair
177 clarity and performance.
179 All code must compile with recent versions of GCC and a number of other
180 currently supported compilers. To ensure compatibility, please do not use
181 additional C99 features or GCC extensions. Especially watch out for:
185 mixing statements and declarations;
188 @samp{long long} (use @samp{int64_t} instead);
191 @samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;
194 GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
197 @subsection Naming conventions
198 All names should be composed with underscores (_), not CamelCase. For example,
199 @samp{avfilter_get_video_buffer} is an acceptable function name and
200 @samp{AVFilterGetVideo} is not. The only exception are structure
201 names; they should always be CamelCase.
203 There are the following conventions for naming variables and functions:
207 For local variables no prefix is required.
210 For file-scope variables and functions declared as @code{static}, no prefix
214 For variables and functions visible outside of file scope, but only used
215 internally by a library, an @code{ff_} prefix should be used,
216 e.g. @samp{ff_w64_demuxer}.
219 For variables and functions visible outside of file scope, used internally
220 across multiple libraries, use @code{avpriv_} as prefix, for example,
221 @samp{avpriv_aac_parse_header}.
224 For externally visible symbols, each library has its own prefix. Check
225 the existing code and choose names accordingly.
228 Furthermore, name space reserved for the system should not be invaded.
229 Identifiers ending in @code{_t} are reserved by
230 @url{http://pubs.opengroup.org/onlinepubs/007904975/functions/xsh_chap02_02.html#tag_02_02_02, POSIX}.
231 Also avoid names starting with @code{__} or @code{_} followed by an uppercase
232 letter as they are reserved by the C standard. Names starting with @code{_}
233 are reserved at the file level and may not be used for externally visible
234 symbols. If in doubt, just avoid names starting with @code{_} altogether.
236 @subsection Miscellaneous conventions
240 fprintf and printf are forbidden in libavformat and libavcodec,
241 please use av_log() instead.
244 Casts should be used only when necessary. Unneeded parentheses
245 should also be avoided if they don't make the code easier to understand.
248 @subsection Editor configuration
249 In order to configure Vim to follow Libav formatting conventions, paste
250 the following snippet into your @file{.vimrc}:
252 " Indentation rules for Libav: 4 spaces, no tabs.
258 " Allow tabs in Makefiles.
259 autocmd FileType make,automake set noexpandtab shiftwidth=8 softtabstop=8
260 " Trailing whitespace and tabs are forbidden, so highlight them.
261 highlight ForbiddenWhitespace ctermbg=red guibg=red
262 match ForbiddenWhitespace /\s\+$\|\t/
263 " Do not highlight spaces at the end of line while typing on that line.
264 autocmd InsertEnter * match ForbiddenWhitespace /\t\|\s\+\%#\@@<!$/
267 For Emacs, add these roughly equivalent lines to your @file{.emacs.d/init.el}:
272 (indent-tabs-mode . nil)
273 (show-trailing-whitespace . t)
275 (statement-cont . (c-lineup-assignments +)))
278 (setq c-default-style "libav")
281 @section Development Policy
285 Contributions should be licensed under the
286 @uref{http://www.gnu.org/licenses/lgpl-2.1.html, LGPL 2.1},
287 including an "or any later version" clause, or, if you prefer
288 a gift-style license, the
289 @uref{http://opensource.org/licenses/isc-license.txt, ISC} or
290 @uref{http://mit-license.org/, MIT} license.
291 @uref{http://www.gnu.org/licenses/gpl-2.0.html, GPL 2} including
292 an "or any later version" clause is also acceptable, but LGPL is
296 All the patches MUST be reviewed in the mailing list before they are
300 The Libav coding style should remain consistent. Changes to
301 conform will be suggested during the review or implemented on commit.
304 Patches should be generated using @code{git format-patch} or directly sent
305 using @code{git send-email}.
306 Please make sure you give the proper credit by setting the correct author
310 The commit message should have a short first line in the form of
311 a @samp{topic: short description} as a header, separated by a newline
312 from the body consisting of an explanation of why the change is necessary.
313 If the commit fixes a known bug on the bug tracker, the commit message
314 should include its bug ID. Referring to the issue on the bug tracker does
315 not exempt you from writing an excerpt of the bug in the commit message.
316 If the patch is a bug fix which should be backported to stable releases,
317 i.e. a non-API/ABI-breaking bug fix, add @code{CC: libav-stable@@libav.org}
318 to the bottom of your commit message, and make sure to CC your patch to
319 this address, too. Some git setups will do this automatically.
322 Work in progress patches should be sent to the mailing list with the [WIP]
326 Branches in public personal repos are advised as way to
327 work on issues collaboratively.
330 You do not have to over-test things. If it works for you and you think it
331 should work for others, send it to the mailing list for review.
332 If you have doubt about portability please state it in the submission so
333 people with specific hardware could test it.
336 Do not commit unrelated changes together, split them into self-contained
337 pieces. Also do not forget that if part B depends on part A, but A does not
338 depend on B, then A can and should be committed first and separate from B.
339 Keeping changes well split into self-contained parts makes reviewing and
340 understanding them on the commit log mailing list easier. This also helps
341 in case of debugging later on.
344 Patches that change behavior of the programs (renaming options etc) or
345 public API or ABI should be discussed in depth and possible few days should
346 pass between discussion and commit.
347 Changes to the build system (Makefiles, configure script) which alter
348 the expected behavior should be considered in the same regard.
351 When applying patches that have been discussed (at length) on the mailing
352 list, reference the thread in the log message.
356 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel} and
357 @uref{https://lists.libav.org/mailman/listinfo/libav-commits, libav-commits}
359 Bugs and possible improvements or general questions regarding commits
360 are discussed on libav-devel. We expect you to react if problems with
361 your code are uncovered.
364 Update the documentation if you change behavior or add features. If you are
365 unsure how best to do this, send an [RFC] patch to libav-devel.
368 All discussions and decisions should be reported on the public developer
369 mailing list, so that there is a reference to them.
370 Other media (e.g. IRC) should be used for coordination and immediate
374 Never write to unallocated memory, never write over the end of arrays,
375 always check values read from some untrusted source before using them
376 as array index or other risky things. Always use valgrind to double-check.
379 Remember to check if you need to bump versions for the specific libav
380 parts (libavutil, libavcodec, libavformat) you are changing. You need
381 to change the version integer.
382 Incrementing the first component means no backward compatibility to
383 previous versions (e.g. removal of a function from the public API).
384 Incrementing the second component means backward compatible change
385 (e.g. addition of a function to the public API or extension of an
386 existing data structure).
387 Incrementing the third component means a noteworthy binary compatible
388 change (e.g. encoder bug fix that matters for the decoder).
391 Compiler warnings indicate potential bugs or code with bad style.
392 If it is a bug, the bug has to be fixed. If it is not, the code should
393 be changed to not generate a warning unless that causes a slowdown
394 or obfuscates the code.
395 If a type of warning leads to too many false positives, that warning
396 should be disabled, not the code changed.
399 If you add a new file, give it a proper license header. Do not copy and
400 paste it from a random place, use an existing file as template.
403 We think our rules are not too hard. If you have comments, contact us.
405 @section Submitting patches
407 First, read the @ref{Coding Rules} above if you did not yet, in particular
408 the rules regarding patch submission.
410 As stated already, please do not submit a patch which contains several
412 Split it into separate, self-contained pieces. This does not mean splitting
413 file by file. Instead, make the patch as small as possible while still
414 keeping it as a logical unit that contains an individual change, even
415 if it spans multiple files. This makes reviewing your patches much easier
416 for us and greatly increases your chances of getting your patch applied.
418 Use the patcheck tool of Libav to check your patch.
419 The tool is located in the tools directory.
421 Run the @ref{Regression Tests} before submitting a patch in order to verify
422 it does not cause unexpected problems.
424 It also helps quite a bit if you tell us what the patch does (for example
425 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
426 and has no lrint()'). This kind of explanation should be the body of the
429 Also please if you send several patches, send each patch as a separate mail,
430 do not attach several unrelated patches to the same mail.
432 Patches should be posted to the
433 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
434 mailing list. Use @code{git send-email} when possible since it will properly
435 send patches without requiring extra care. If you cannot, then send patches
436 as base64-encoded attachments, so your patch is not trashed during
439 Your patch will be reviewed on the mailing list. You will likely be asked
440 to make some changes and are expected to send in an improved version that
441 incorporates the requests from the review. This process may go through
442 several iterations. Once your patch is deemed good enough, it will be
443 committed to the official Libav tree.
445 Give us a few days to react. But if some time passes without reaction,
446 send a reminder by email. Your patch should eventually be dealt with.
449 @section New codecs or formats checklist
453 Did you use av_cold for codec initialization and close functions?
456 Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
457 AVInputFormat/AVOutputFormat struct?
460 Did you bump the minor version number (and reset the micro version
461 number) in @file{libavcodec/version.h} or @file{libavformat/version.h}?
464 Did you register it in @file{allcodecs.c} or @file{allformats.c}?
467 Did you add the AVCodecID to @file{avcodec.h}?
468 When adding new codec IDs, also add an entry to the codec descriptor
469 list in @file{libavcodec/codec_desc.c}.
472 If it has a FourCC, did you add it to @file{libavformat/riff.c},
473 even if it is only a decoder?
476 Did you add a rule to compile the appropriate files in the Makefile?
477 Remember to do this even if you are just adding a format to a file that
478 is already being compiled by some other rule, like a raw demuxer.
481 Did you add an entry to the table of supported formats or codecs in
482 @file{doc/general.texi}?
485 Did you add an entry in the Changelog?
488 If it depends on a parser or a library, did you add that dependency in
492 Did you @code{git add} the appropriate files before committing?
495 Did you make sure it compiles standalone, i.e. with
496 @code{configure --disable-everything --enable-decoder=foo}
497 (or @code{--enable-demuxer} or whatever your component is)?
501 @section patch submission checklist
505 Does @code{make check} pass with the patch applied?
508 Is the patch against latest Libav git master branch?
511 Are you subscribed to the
512 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
513 mailing list? (Only list subscribers are allowed to post.)
516 Have you checked that the changes are minimal, so that the same cannot be
517 achieved with a smaller patch and/or simpler final code?
520 If the change is to speed critical code, did you benchmark it?
523 If you did any benchmarks, did you provide them in the mail?
526 Have you checked that the patch does not introduce buffer overflows or
527 other security issues?
530 Did you test your decoder or demuxer against damaged data? If no, see
531 tools/trasher, the noise bitstream filter, and
532 @uref{http://caca.zoy.org/wiki/zzuf, zzuf}. Your decoder or demuxer
533 should not crash, end in a (near) infinite loop, or allocate ridiculous
534 amounts of memory when fed damaged data.
537 Does the patch not mix functional and cosmetic changes?
540 Did you add tabs or trailing whitespace to the code? Both are forbidden.
543 Is the patch attached to the email you send?
546 Is the mime type of the patch correct? It should be text/x-diff or
547 text/x-patch or at least text/plain and not application/octet-stream.
550 If the patch fixes a bug, did you provide a verbose analysis of the bug?
553 If the patch fixes a bug, did you provide enough information, including
554 a sample, so the bug can be reproduced and the fix can be verified?
555 Note please do not attach samples >100k to mails but rather provide a
556 URL, you can upload to ftp://upload.libav.org
559 Did you provide a verbose summary about what the patch does change?
562 Did you provide a verbose explanation why it changes things like it does?
565 Did you provide a verbose summary of the user visible advantages and
566 disadvantages if the patch is applied?
569 Did you provide an example so we can verify the new feature added by the
573 If you added a new file, did you insert a license header? It should be
574 taken from Libav, not randomly copied and pasted from somewhere else.
577 You should maintain alphabetical order in alphabetically ordered lists as
578 long as doing so does not break API/ABI compatibility.
581 Lines with similar content should be aligned vertically when doing so
582 improves readability.
585 Make sure you check the return values of function and return appropriate
586 error codes. Especially memory allocation functions like @code{malloc()}
587 are notoriously left unchecked, which is a serious problem.
590 @section Patch review process
592 All patches posted to the
593 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
594 mailing list will be reviewed, unless they contain a
595 clear note that the patch is not for the git master branch.
596 Reviews and comments will be posted as replies to the patch on the
597 mailing list. The patch submitter then has to take care of every comment,
598 that can be by resubmitting a changed patch or by discussion. Resubmitted
599 patches will themselves be reviewed like any other patch. If at some point
600 a patch passes review with no comments then it is approved, that can for
601 simple and small patches happen immediately while large patches will generally
602 have to be changed and reviewed many times before they are approved.
603 After a patch is approved it will be committed to the repository.
605 We will review all submitted patches, but sometimes we are quite busy so
606 especially for large patches this can take several weeks.
608 When resubmitting patches, if their size grew or during the review different
609 issues arisen please split the patch so each issue has a specific patch.
611 @anchor{Regression Tests}
612 @section Regression Tests
614 Before submitting a patch (or committing to the repository), you should at
615 least make sure that it does not break anything.
617 If the code changed has already a test present in FATE you should run it,
618 otherwise it is advised to add it.
620 Improvements to codec or demuxer might change the FATE results. Make sure
621 to commit the update reference with the change and to explain in the comment
622 why the expected result changed.
624 Please refer to @url{fate.html}.
626 @subsection Visualizing Test Coverage
628 The Libav build system allows visualizing the test coverage in an easy
629 manner with the coverage tools @code{gcov}/@code{lcov}. This involves
634 Configure to compile with instrumentation enabled:
635 @code{configure --toolchain=gcov}.
638 Run your test case, either manually or via FATE. This can be either
639 the full FATE regression suite, or any arbitrary invocation of any
640 front-end tool provided by Libav, in any combination.
643 Run @code{make lcov} to generate coverage data in HTML format.
646 View @code{lcov/index.html} in your preferred HTML viewer.
649 You can use the command @code{make lcov-reset} to reset the coverage
650 measurements. You will need to rerun @code{make lcov} after running a
653 @subsection Using Valgrind
655 The configure script provides a shortcut for using valgrind to spot bugs
656 related to memory handling. Just add the option
657 @code{--toolchain=valgrind-memcheck} or @code{--toolchain=valgrind-massif}
658 to your configure line, and reasonable defaults will be set for running
659 FATE under the supervision of either the @strong{memcheck} or the
660 @strong{massif} tool of the valgrind suite.
662 In case you need finer control over how valgrind is invoked, use the
663 @code{--target-exec='valgrind <your_custom_valgrind_options>} option in
664 your configure line instead.
666 @anchor{Release process}
667 @section Release process
669 Libav maintains a set of @strong{release branches}, which are the
670 recommended deliverable for system integrators and distributors (such as
671 Linux distributions, etc.). At irregular times, a @strong{release
672 manager} prepares, tests and publishes tarballs on the
673 @url{http://libav.org} website.
675 There are two kinds of releases:
679 @strong{Major releases} always include the latest and greatest
680 features and functionality.
683 @strong{Point releases} are cut from @strong{release} branches,
684 which are named @code{release/X}, with @code{X} being the release
688 Note that we promise to our users that shared libraries from any Libav
689 release never break programs that have been @strong{compiled} against
690 previous versions of @strong{the same release series} in any case!
692 However, from time to time, we do make API changes that require adaptations
693 in applications. Such changes are only allowed in (new) major releases and
694 require further steps such as bumping library version numbers and/or
695 adjustments to the symbol versioning file. Please discuss such changes
696 on the @strong{libav-devel} mailing list in time to allow forward planning.
698 @anchor{Criteria for Point Releases}
699 @subsection Criteria for Point Releases
701 Changes that match the following criteria are valid candidates for
702 inclusion into a point release:
706 Fixes a security issue, preferably identified by a @strong{CVE
707 number} issued by @url{http://cve.mitre.org/}.
710 Fixes a documented bug in @url{http://bugzilla.libav.org}.
713 Improves the included documentation.
716 Retains both source code and binary compatibility with previous
717 point releases of the same release branch.
720 The order for checking the rules is (1 OR 2 OR 3) AND 4.
722 All Libav developers are welcome to nominate commits that they push to
723 @code{master} by mailing the @strong{libav-stable} mailing list. The
724 easiest way to do so is to include @code{CC: libav-stable@@libav.org} in
728 @subsection Release Checklist
730 The release process involves the following steps:
734 Ensure that the @file{RELEASE} file contains the version number for
735 the upcoming release.
738 File a release tracking bug in @url{http://bugzilla.libav.org}. Make
739 sure that the bug has an alias named @code{ReleaseX.Y} for the
743 Announce the intent to do a release to the mailing list.
746 Reassign unresolved blocking bugs from previous release
747 tracking bugs to the new bug.
750 Review patch nominations that reach the @strong{libav-stable}
751 mailing list, and push patches that fulfill the stable release
752 criteria to the release branch.
755 Ensure that the FATE regression suite still passes in the release
756 branch on at least @strong{i386} and @strong{amd64}
757 (cf. @ref{Regression Tests}).
760 Prepare the release tarballs in @code{xz} and @code{gz} formats, and
761 supplementing files that contain @code{md5} and @code{sha1}
765 Publish the tarballs at @url{http://libav.org/releases}. Create and
766 push an annotated tag in the form @code{vX}, with @code{X}
767 containing the version number.
770 Build the tarballs with the Windows binaries, and publish them at
771 @url{http://win32.libav.org/releases}.
774 Propose and send a patch to the @strong{libav-devel} mailing list
775 with a news entry for the website.
778 Publish the news entry.
781 Send announcement to the mailing list.