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{libavcodec/apiexample.c} to see how to use it.
19 @item libavformat is the library containing the file format handling (mux and
20 demux code for several formats). Look at @file{avplay.c} to use it in a
21 player. See @file{libavformat/output-example.c} to use it to generate
22 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:
52 The control statements are formatted by putting space between the statement
53 and parenthesis in the following way:
55 for (i = 0; i < filter->input_count; i++) @{
58 The case statement is always located at the same level as the switch itself:
60 switch (link->init_state) @{
63 case AVLINK_STARTINIT:
64 av_log(filter, AV_LOG_INFO, "circular filter chain detected");
68 Braces in function declarations are written on the new line:
70 const char *avfilter_configuration(void)
72 return LIBAV_CONFIGURATION;
76 Do not check for NULL values by comparison, @samp{if (p)} and
77 @samp{if (!p)} are correct; @samp{if (p == NULL)} and @samp{if (p != NULL)}
80 In case of a single-statement if, no curly braces are required:
86 Do not put spaces immediately inside parentheses. @samp{if (ret)} is
87 a valid style; @samp{if ( ret )} is not.
90 There are the following guidelines regarding the indentation in files:
95 The TAB character is forbidden outside of Makefiles as is any
96 form of trailing whitespace. Commits containing either will be
97 rejected by the git repository.
99 You should try to limit your code lines to 80 characters; however, do so if
100 and only if this improves readability.
102 The presentation is one inspired by 'indent -i4 -kr -nut'.
104 The main priority in Libav is simplicity and small code size in order to
105 minimize the bug count.
108 Use the JavaDoc/Doxygen format (see examples below) so that code documentation
109 can be generated automatically. All nontrivial functions should have a comment
110 above them explaining what the function does, even if it is just one sentence.
111 All structures and their member variables should be documented, too.
113 Avoid Qt-style and similar Doxygen syntax with @code{!} in it, i.e. replace
114 @code{//!} with @code{///} and similar. Also @@ syntax should be employed
115 for markup commands, i.e. use @code{@@param} and not @code{\param}.
129 typedef struct Foobar@{
130 int var1; /**< var1 description */
131 int var2; ///< var2 description
132 /** var3 description */
140 * @@param my_parameter description of my_parameter
141 * @@return return value description
143 int myfunc(int my_parameter)
147 @subsection C language features
149 Libav is programmed in the ISO C90 language with a few additional
150 features from ISO C99, namely:
153 the @samp{inline} keyword;
157 designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
159 compound literals (@samp{x = (struct s) @{ 17, 23 @};})
162 These features are supported by all compilers we care about, so we will not
163 accept patches to remove their use unless they absolutely do not impair
164 clarity and performance.
166 All code must compile with recent versions of GCC and a number of other
167 currently supported compilers. To ensure compatibility, please do not use
168 additional C99 features or GCC extensions. Especially watch out for:
171 mixing statements and declarations;
173 @samp{long long} (use @samp{int64_t} instead);
175 @samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;
177 GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
180 @subsection Naming conventions
181 All names should be composed with underscores (_), not CamelCase. For example,
182 @samp{avfilter_get_video_buffer} is an acceptable function name and
183 @samp{AVFilterGetVideo} is not. The only exception are structure
184 names; they should always be CamelCase.
186 There are the following conventions for naming variables and functions:
189 For local variables no prefix is required.
191 For file-scope variables and functions declared as @code{static}, no prefix
194 For variables and functions visible outside of file scope, but only used
195 internally by a library, an @code{ff_} prefix should be used,
196 e.g. @samp{ff_w64_demuxer}.
198 For variables and functions visible outside of file scope, used internally
199 across multiple libraries, use @code{avpriv_} as prefix, for example,
200 @samp{avpriv_aac_parse_header}.
202 For externally visible symbols, each library has its own prefix. Check
203 the existing code and choose names accordingly.
206 Furthermore, name space reserved for the system should not be invaded.
207 Identifiers ending in @code{_t} are reserved by
208 @url{http://pubs.opengroup.org/onlinepubs/007904975/functions/xsh_chap02_02.html#tag_02_02_02, POSIX}.
209 Also avoid names starting with @code{__} or @code{_} followed by an uppercase
210 letter as they are reserved by the C standard. Names starting with @code{_}
211 are reserved at the file level and may not be used for externally visible
212 symbols. If in doubt, just avoid names starting with @code{_} altogether.
214 @subsection Miscellaneous conventions
217 fprintf and printf are forbidden in libavformat and libavcodec,
218 please use av_log() instead.
220 Casts should be used only when necessary. Unneeded parentheses
221 should also be avoided if they don't make the code easier to understand.
224 @subsection Editor configuration
225 In order to configure Vim to follow Libav formatting conventions, paste
226 the following snippet into your @file{.vimrc}:
228 " Indentation rules for Libav: 4 spaces, no tabs.
234 " Allow tabs in Makefiles.
235 autocmd FileType make,automake set noexpandtab shiftwidth=8 softtabstop=8
236 " Trailing whitespace and tabs are forbidden, so highlight them.
237 highlight ForbiddenWhitespace ctermbg=red guibg=red
238 match ForbiddenWhitespace /\s\+$\|\t/
239 " Do not highlight spaces at the end of line while typing on that line.
240 autocmd InsertEnter * match ForbiddenWhitespace /\t\|\s\+\%#\@@<!$/
243 For Emacs, add these roughly equivalent lines to your @file{.emacs.d/init.el}:
248 (indent-tabs-mode . nil)
249 (show-trailing-whitespace . t)
251 (statement-cont . (c-lineup-assignments +)))
254 (setq c-default-style "libav")
257 @section Development Policy
261 Contributions should be licensed under the
262 @uref{http://www.gnu.org/licenses/lgpl-2.1.html, LGPL 2.1},
263 including an "or any later version" clause, or, if you prefer
264 a gift-style license, the
265 @uref{http://www.isc.org/software/license/, ISC} or
266 @uref{http://mit-license.org/, MIT} license.
267 @uref{http://www.gnu.org/licenses/gpl-2.0.html, GPL 2} including
268 an "or any later version" clause is also acceptable, but LGPL is
271 All the patches MUST be reviewed in the mailing list before they are
274 The Libav coding style should remain consistent. Changes to
275 conform will be suggested during the review or implemented on commit.
277 Patches should be generated using @code{git format-patch} or directly sent
278 using @code{git send-email}.
279 Please make sure you give the proper credit by setting the correct author
282 The commit message should have a short first line in the form of
283 a @samp{topic: short description} as a header, separated by a newline
284 from the body consisting of an explanation of why the change is necessary.
285 If the commit fixes a known bug on the bug tracker, the commit message
286 should include its bug ID. Referring to the issue on the bug tracker does
287 not exempt you from writing an excerpt of the bug in the commit message.
288 If the patch is a bug fix which should be backported to stable releases,
289 i.e. a non-API/ABI-breaking bug fix, add @code{CC: libav-stable@@libav.org}
290 to the bottom of your commit message, and make sure to CC your patch to
291 this address, too. Some git setups will do this automatically.
293 Work in progress patches should be sent to the mailing list with the [WIP]
296 Branches in public personal repos are advised as way to
297 work on issues collaboratively.
299 You do not have to over-test things. If it works for you and you think it
300 should work for others, send it to the mailing list for review.
301 If you have doubt about portability please state it in the submission so
302 people with specific hardware could test it.
304 Do not commit unrelated changes together, split them into self-contained
305 pieces. Also do not forget that if part B depends on part A, but A does not
306 depend on B, then A can and should be committed first and separate from B.
307 Keeping changes well split into self-contained parts makes reviewing and
308 understanding them on the commit log mailing list easier. This also helps
309 in case of debugging later on.
311 Patches that change behavior of the programs (renaming options etc) or
312 public API or ABI should be discussed in depth and possible few days should
313 pass between discussion and commit.
314 Changes to the build system (Makefiles, configure script) which alter
315 the expected behavior should be considered in the same regard.
317 When applying patches that have been discussed (at length) on the mailing
318 list, reference the thread in the log message.
321 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel} and
322 @uref{https://lists.libav.org/mailman/listinfo/libav-commits, libav-commits}
324 Bugs and possible improvements or general questions regarding commits
325 are discussed on libav-devel. We expect you to react if problems with
326 your code are uncovered.
328 Update the documentation if you change behavior or add features. If you are
329 unsure how best to do this, send an [RFC] patch to libav-devel.
331 All discussions and decisions should be reported on the public developer
332 mailing list, so that there is a reference to them.
333 Other media (e.g. IRC) should be used for coordination and immediate
336 Never write to unallocated memory, never write over the end of arrays,
337 always check values read from some untrusted source before using them
338 as array index or other risky things. Always use valgrind to double-check.
340 Remember to check if you need to bump versions for the specific libav
341 parts (libavutil, libavcodec, libavformat) you are changing. You need
342 to change the version integer.
343 Incrementing the first component means no backward compatibility to
344 previous versions (e.g. removal of a function from the public API).
345 Incrementing the second component means backward compatible change
346 (e.g. addition of a function to the public API or extension of an
347 existing data structure).
348 Incrementing the third component means a noteworthy binary compatible
349 change (e.g. encoder bug fix that matters for the decoder).
351 Compiler warnings indicate potential bugs or code with bad style.
352 If it is a bug, the bug has to be fixed. If it is not, the code should
353 be changed to not generate a warning unless that causes a slowdown
354 or obfuscates the code.
355 If a type of warning leads to too many false positives, that warning
356 should be disabled, not the code changed.
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 @section Submitting patches
366 First, read the @ref{Coding Rules} above if you did not yet, in particular
367 the rules regarding patch submission.
369 As stated already, please do not submit a patch which contains several
371 Split it into separate, self-contained pieces. This does not mean splitting
372 file by file. Instead, make the patch as small as possible while still
373 keeping it as a logical unit that contains an individual change, even
374 if it spans multiple files. This makes reviewing your patches much easier
375 for us and greatly increases your chances of getting your patch applied.
377 Use the patcheck tool of Libav to check your patch.
378 The tool is located in the tools directory.
380 Run the @ref{Regression Tests} before submitting a patch in order to verify
381 it does not cause unexpected problems.
383 It also helps quite a bit if you tell us what the patch does (for example
384 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
385 and has no lrint()'). This kind of explanation should be the body of the
388 Also please if you send several patches, send each patch as a separate mail,
389 do not attach several unrelated patches to the same mail.
391 Patches should be posted to the
392 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
393 mailing list. Use @code{git send-email} when possible since it will properly
394 send patches without requiring extra care. If you cannot, then send patches
395 as base64-encoded attachments, so your patch is not trashed during
398 Your patch will be reviewed on the mailing list. You will likely be asked
399 to make some changes and are expected to send in an improved version that
400 incorporates the requests from the review. This process may go through
401 several iterations. Once your patch is deemed good enough, it will be
402 committed to the official Libav tree.
404 Give us a few days to react. But if some time passes without reaction,
405 send a reminder by email. Your patch should eventually be dealt with.
408 @section New codecs or formats checklist
412 Did you use av_cold for codec initialization and close functions?
414 Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
415 AVInputFormat/AVOutputFormat struct?
417 Did you bump the minor version number (and reset the micro version
418 number) in @file{libavcodec/version.h} or @file{libavformat/version.h}?
420 Did you register it in @file{allcodecs.c} or @file{allformats.c}?
422 Did you add the AVCodecID to @file{avcodec.h}?
423 When adding new codec IDs, also add an entry to the codec descriptor
424 list in @file{libavcodec/codec_desc.c}.
426 If it has a FourCC, did you add it to @file{libavformat/riff.c},
427 even if it is only a decoder?
429 Did you add a rule to compile the appropriate files in the Makefile?
430 Remember to do this even if you are just adding a format to a file that
431 is already being compiled by some other rule, like a raw demuxer.
433 Did you add an entry to the table of supported formats or codecs in
434 @file{doc/general.texi}?
436 Did you add an entry in the Changelog?
438 If it depends on a parser or a library, did you add that dependency in
441 Did you @code{git add} the appropriate files before committing?
443 Did you make sure it compiles standalone, i.e. with
444 @code{configure --disable-everything --enable-decoder=foo}
445 (or @code{--enable-demuxer} or whatever your component is)?
449 @section patch submission checklist
453 Does @code{make check} pass with the patch applied?
455 Is the patch against latest Libav git master branch?
457 Are you subscribed to the
458 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
459 mailing list? (Only list subscribers are allowed to post.)
461 Have you checked that the changes are minimal, so that the same cannot be
462 achieved with a smaller patch and/or simpler final code?
464 If the change is to speed critical code, did you benchmark it?
466 If you did any benchmarks, did you provide them in the mail?
468 Have you checked that the patch does not introduce buffer overflows or
469 other security issues?
471 Did you test your decoder or demuxer against damaged data? If no, see
472 tools/trasher, the noise bitstream filter, and
473 @uref{http://caca.zoy.org/wiki/zzuf, zzuf}. Your decoder or demuxer
474 should not crash, end in a (near) infinite loop, or allocate ridiculous
475 amounts of memory when fed damaged data.
477 Does the patch not mix functional and cosmetic changes?
479 Did you add tabs or trailing whitespace to the code? Both are forbidden.
481 Is the patch attached to the email you send?
483 Is the mime type of the patch correct? It should be text/x-diff or
484 text/x-patch or at least text/plain and not application/octet-stream.
486 If the patch fixes a bug, did you provide a verbose analysis of the bug?
488 If the patch fixes a bug, did you provide enough information, including
489 a sample, so the bug can be reproduced and the fix can be verified?
490 Note please do not attach samples >100k to mails but rather provide a
491 URL, you can upload to ftp://upload.libav.org
493 Did you provide a verbose summary about what the patch does change?
495 Did you provide a verbose explanation why it changes things like it does?
497 Did you provide a verbose summary of the user visible advantages and
498 disadvantages if the patch is applied?
500 Did you provide an example so we can verify the new feature added by the
503 If you added a new file, did you insert a license header? It should be
504 taken from Libav, not randomly copied and pasted from somewhere else.
506 You should maintain alphabetical order in alphabetically ordered lists as
507 long as doing so does not break API/ABI compatibility.
509 Lines with similar content should be aligned vertically when doing so
510 improves readability.
512 Make sure you check the return values of function and return appropriate
513 error codes. Especially memory allocation functions like @code{malloc()}
514 are notoriously left unchecked, which is a serious problem.
517 @section Patch review process
519 All patches posted to the
520 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
521 mailing list will be reviewed, unless they contain a
522 clear note that the patch is not for the git master branch.
523 Reviews and comments will be posted as replies to the patch on the
524 mailing list. The patch submitter then has to take care of every comment,
525 that can be by resubmitting a changed patch or by discussion. Resubmitted
526 patches will themselves be reviewed like any other patch. If at some point
527 a patch passes review with no comments then it is approved, that can for
528 simple and small patches happen immediately while large patches will generally
529 have to be changed and reviewed many times before they are approved.
530 After a patch is approved it will be committed to the repository.
532 We will review all submitted patches, but sometimes we are quite busy so
533 especially for large patches this can take several weeks.
535 When resubmitting patches, if their size grew or during the review different
536 issues arisen please split the patch so each issue has a specific patch.
538 @anchor{Regression Tests}
539 @section Regression Tests
541 Before submitting a patch (or committing to the repository), you should at
542 least make sure that it does not break anything.
544 If the code changed has already a test present in FATE you should run it,
545 otherwise it is advised to add it.
547 Improvements to codec or demuxer might change the FATE results. Make sure
548 to commit the update reference with the change and to explain in the comment
549 why the expected result changed.
551 Please refer to @url{fate.html}.
553 @subsection Visualizing Test Coverage
555 The Libav build system allows visualizing the test coverage in an easy
556 manner with the coverage tools @code{gcov}/@code{lcov}. This involves
561 Configure to compile with instrumentation enabled:
562 @code{configure --toolchain=gcov}.
564 Run your test case, either manually or via FATE. This can be either
565 the full FATE regression suite, or any arbitrary invocation of any
566 front-end tool provided by Libav, in any combination.
568 Run @code{make lcov} to generate coverage data in HTML format.
570 View @code{lcov/index.html} in your preferred HTML viewer.
573 You can use the command @code{make lcov-reset} to reset the coverage
574 measurements. You will need to rerun @code{make lcov} after running a
577 @anchor{Release process}
578 @section Release process
580 Libav maintains a set of @strong{release branches}, which are the
581 recommended deliverable for system integrators and distributors (such as
582 Linux distributions, etc.). At irregular times, a @strong{release
583 manager} prepares, tests and publishes tarballs on the
584 @url{http://libav.org} website.
586 There are two kinds of releases:
590 @strong{Major releases} always include the latest and greatest
591 features and functionality.
593 @strong{Point releases} are cut from @strong{release} branches,
594 which are named @code{release/X}, with @code{X} being the release
598 Note that we promise to our users that shared libraries from any Libav
599 release never break programs that have been @strong{compiled} against
600 previous versions of @strong{the same release series} in any case!
602 However, from time to time, we do make API changes that require adaptations
603 in applications. Such changes are only allowed in (new) major releases and
604 require further steps such as bumping library version numbers and/or
605 adjustments to the symbol versioning file. Please discuss such changes
606 on the @strong{libav-devel} mailing list in time to allow forward planning.
608 @anchor{Criteria for Point Releases}
609 @subsection Criteria for Point Releases
611 Changes that match the following criteria are valid candidates for
612 inclusion into a point release:
616 Fixes a security issue, preferably identified by a @strong{CVE
617 number} issued by @url{http://cve.mitre.org/}.
619 Fixes a documented bug in @url{http://bugzilla.libav.org}.
621 Improves the included documentation.
623 Retains both source code and binary compatibility with previous
624 point releases of the same release branch.
627 The order for checking the rules is (1 OR 2 OR 3) AND 4.
629 All Libav developers are welcome to nominate commits that they push to
630 @code{master} by mailing the @strong{libav-stable} mailing list. The
631 easiest way to do so is to include @code{CC: libav-stable@@libav.org} in
635 @subsection Release Checklist
637 The release process involves the following steps:
641 Ensure that the @file{RELEASE} file contains the version number for
642 the upcoming release.
644 File a release tracking bug in @url{http://bugzilla.libav.org}. Make
645 sure that the bug has an alias named @code{ReleaseX.Y} for the
648 Announce the intent to do a release to the mailing list.
650 Reassign unresolved blocking bugs from previous release
651 tracking bugs to the new bug.
653 Review patch nominations that reach the @strong{libav-stable}
654 mailing list, and push patches that fulfill the stable release
655 criteria to the release branch.
657 Ensure that the FATE regression suite still passes in the release
658 branch on at least @strong{i386} and @strong{amd64}
659 (cf. @ref{Regression Tests}).
661 Prepare the release tarballs in @code{xz} and @code{gz} formats, and
662 supplementing files that contain @code{md5} and @code{sha1}
665 Publish the tarballs at @url{http://libav.org/releases}. Create and
666 push an annotated tag in the form @code{vX}, with @code{X}
667 containing the version number.
669 Build the tarballs with the Windows binaries, and publish them at
670 @url{http://win32.libav.org/releases}.
672 Propose and send a patch to the @strong{libav-devel} mailing list
673 with a news entry for the website.
675 Publish the news entry.
677 Send announcement to the mailing list.