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 are using underscores (_), not CamelCase. For example,
182 @samp{avfilter_get_video_buffer} is a valid function name and
183 @samp{AVFilterGetVideo} is not. The only exception from this are structure
184 names; they should always be in the CamelCase
186 There are following conventions for naming variables and functions:
189 For local variables no prefix is required.
191 For variables and functions declared as @code{static} no prefixes are required.
193 For variables and functions used internally by the library, @code{ff_} prefix
195 For example, @samp{ff_w64_demuxer}.
197 For variables and functions used internally across multiple libraries, use
198 @code{avpriv_}. For example, @samp{avpriv_aac_parse_header}.
200 For exported names, each library has its own prefixes. Just check the existing
201 code and name accordingly.
204 @subsection Miscellaneous conventions
207 fprintf and printf are forbidden in libavformat and libavcodec,
208 please use av_log() instead.
210 Casts should be used only when necessary. Unneeded parentheses
211 should also be avoided if they don't make the code easier to understand.
214 @subsection Editor configuration
215 In order to configure Vim to follow Libav formatting conventions, paste
216 the following snippet into your @file{.vimrc}:
218 " Indentation rules for Libav: 4 spaces, no tabs.
224 " Allow tabs in Makefiles.
225 autocmd FileType make set noexpandtab shiftwidth=8 softtabstop=8
226 " Trailing whitespace and tabs are forbidden, so highlight them.
227 highlight ForbiddenWhitespace ctermbg=red guibg=red
228 match ForbiddenWhitespace /\s\+$\|\t/
229 " Do not highlight spaces at the end of line while typing on that line.
230 autocmd InsertEnter * match ForbiddenWhitespace /\t\|\s\+\%#\@@<!$/
233 For Emacs, add these roughly equivalent lines to your @file{.emacs.d/init.el}:
238 (indent-tabs-mode . nil)
239 (show-trailing-whitespace . t)
241 (statement-cont . (c-lineup-assignments +)))
244 (setq c-default-style "libav")
247 @section Development Policy
251 Contributions should be licensed under the LGPL 2.1, including an
252 "or any later version" clause, or the MIT license. GPL 2 including
253 an "or any later version" clause is also acceptable, but LGPL is
256 All the patches MUST be reviewed in the mailing list before they are
259 The Libav coding style should remain consistent. Changes to
260 conform will be suggested during the review or implemented on commit.
262 Patches should be generated using @code{git format-patch} or directly sent
263 using @code{git send-email}.
264 Please make sure you give the proper credit by setting the correct author
267 The commit message should have a short first line in the form of
268 a @samp{topic: short description} as a header, separated by a newline
269 from the body consisting of an explanation of why the change is necessary.
270 If the commit fixes a known bug on the bug tracker, the commit message
271 should include its bug ID. Referring to the issue on the bug tracker does
272 not exempt you from writing an excerpt of the bug in the commit message.
273 If the patch is a bug fix which should be backported to stable releases,
274 i.e. a non-API/ABI-breaking bug fix, add @code{CC: libav-stable@@libav.org}
275 to the bottom of your commit message, and make sure to CC your patch to
276 this address, too. Some git setups will do this automatically.
278 Work in progress patches should be sent to the mailing list with the [WIP]
281 Branches in public personal repos are advised as way to
282 work on issues collaboratively.
284 You do not have to over-test things. If it works for you and you think it
285 should work for others, send it to the mailing list for review.
286 If you have doubt about portability please state it in the submission so
287 people with specific hardware could test it.
289 Do not commit unrelated changes together, split them into self-contained
290 pieces. Also do not forget that if part B depends on part A, but A does not
291 depend on B, then A can and should be committed first and separate from B.
292 Keeping changes well split into self-contained parts makes reviewing and
293 understanding them on the commit log mailing list easier. This also helps
294 in case of debugging later on.
296 Patches that change behavior of the programs (renaming options etc) or
297 public API or ABI should be discussed in depth and possible few days should
298 pass between discussion and commit.
299 Changes to the build system (Makefiles, configure script) which alter
300 the expected behavior should be considered in the same regard.
302 When applying patches that have been discussed (at length) on the mailing
303 list, reference the thread in the log message.
306 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel} and
307 @uref{https://lists.libav.org/mailman/listinfo/libav-commits, libav-commits}
309 Bugs and possible improvements or general questions regarding commits
310 are discussed on libav-devel. We expect you to react if problems with
311 your code are uncovered.
313 Update the documentation if you change behavior or add features. If you are
314 unsure how best to do this, send an [RFC] patch to libav-devel.
316 All discussions and decisions should be reported on the public developer
317 mailing list, so that there is a reference to them.
318 Other media (e.g. IRC) should be used for coordination and immediate
321 Never write to unallocated memory, never write over the end of arrays,
322 always check values read from some untrusted source before using them
323 as array index or other risky things. Always use valgrind to double-check.
325 Remember to check if you need to bump versions for the specific libav
326 parts (libavutil, libavcodec, libavformat) you are changing. You need
327 to change the version integer.
328 Incrementing the first component means no backward compatibility to
329 previous versions (e.g. removal of a function from the public API).
330 Incrementing the second component means backward compatible change
331 (e.g. addition of a function to the public API or extension of an
332 existing data structure).
333 Incrementing the third component means a noteworthy binary compatible
334 change (e.g. encoder bug fix that matters for the decoder).
336 Compiler warnings indicate potential bugs or code with bad style.
337 If it is a bug, the bug has to be fixed. If it is not, the code should
338 be changed to not generate a warning unless that causes a slowdown
339 or obfuscates the code.
340 If a type of warning leads to too many false positives, that warning
341 should be disabled, not the code changed.
343 If you add a new file, give it a proper license header. Do not copy and
344 paste it from a random place, use an existing file as template.
347 We think our rules are not too hard. If you have comments, contact us.
349 Note, some rules were borrowed from the MPlayer project.
351 @section Submitting patches
353 First, read the @ref{Coding Rules} above if you did not yet, in particular
354 the rules regarding patch submission.
356 As stated already, please do not submit a patch which contains several
358 Split it into separate, self-contained pieces. This does not mean splitting
359 file by file. Instead, make the patch as small as possible while still
360 keeping it as a logical unit that contains an individual change, even
361 if it spans multiple files. This makes reviewing your patches much easier
362 for us and greatly increases your chances of getting your patch applied.
364 Use the patcheck tool of Libav to check your patch.
365 The tool is located in the tools directory.
367 Run the @ref{Regression Tests} before submitting a patch in order to verify
368 it does not cause unexpected problems.
370 It also helps quite a bit if you tell us what the patch does (for example
371 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
372 and has no lrint()'). This kind of explanation should be the body of the
375 Also please if you send several patches, send each patch as a separate mail,
376 do not attach several unrelated patches to the same mail.
378 Patches should be posted to the
379 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
380 mailing list. Use @code{git send-email} when possible since it will properly
381 send patches without requiring extra care. If you cannot, then send patches
382 as base64-encoded attachments, so your patch is not trashed during
385 Your patch will be reviewed on the mailing list. You will likely be asked
386 to make some changes and are expected to send in an improved version that
387 incorporates the requests from the review. This process may go through
388 several iterations. Once your patch is deemed good enough, it will be
389 committed to the official Libav tree.
391 Give us a few days to react. But if some time passes without reaction,
392 send a reminder by email. Your patch should eventually be dealt with.
395 @section New codecs or formats checklist
399 Did you use av_cold for codec initialization and close functions?
401 Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
402 AVInputFormat/AVOutputFormat struct?
404 Did you bump the minor version number (and reset the micro version
405 number) in @file{libavcodec/version.h} or @file{libavformat/version.h}?
407 Did you register it in @file{allcodecs.c} or @file{allformats.c}?
409 Did you add the AVCodecID to @file{avcodec.h}?
410 When adding new codec IDs, also add an entry to the codec descriptor
411 list in @file{libavcodec/codec_desc.c}.
413 If it has a FourCC, did you add it to @file{libavformat/riff.c},
414 even if it is only a decoder?
416 Did you add a rule to compile the appropriate files in the Makefile?
417 Remember to do this even if you are just adding a format to a file that
418 is already being compiled by some other rule, like a raw demuxer.
420 Did you add an entry to the table of supported formats or codecs in
421 @file{doc/general.texi}?
423 Did you add an entry in the Changelog?
425 If it depends on a parser or a library, did you add that dependency in
428 Did you @code{git add} the appropriate files before committing?
430 Did you make sure it compiles standalone, i.e. with
431 @code{configure --disable-everything --enable-decoder=foo}
432 (or @code{--enable-demuxer} or whatever your component is)?
436 @section patch submission checklist
440 Does @code{make check} pass with the patch applied?
442 Is the patch against latest Libav git master branch?
444 Are you subscribed to the
445 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
446 mailing list? (Only list subscribers are allowed to post.)
448 Have you checked that the changes are minimal, so that the same cannot be
449 achieved with a smaller patch and/or simpler final code?
451 If the change is to speed critical code, did you benchmark it?
453 If you did any benchmarks, did you provide them in the mail?
455 Have you checked that the patch does not introduce buffer overflows or
456 other security issues?
458 Did you test your decoder or demuxer against damaged data? If no, see
459 tools/trasher, the noise bitstream filter, and
460 @uref{http://caca.zoy.org/wiki/zzuf, zzuf}. Your decoder or demuxer
461 should not crash, end in a (near) infinite loop, or allocate ridiculous
462 amounts of memory when fed damaged data.
464 Does the patch not mix functional and cosmetic changes?
466 Did you add tabs or trailing whitespace to the code? Both are forbidden.
468 Is the patch attached to the email you send?
470 Is the mime type of the patch correct? It should be text/x-diff or
471 text/x-patch or at least text/plain and not application/octet-stream.
473 If the patch fixes a bug, did you provide a verbose analysis of the bug?
475 If the patch fixes a bug, did you provide enough information, including
476 a sample, so the bug can be reproduced and the fix can be verified?
477 Note please do not attach samples >100k to mails but rather provide a
478 URL, you can upload to ftp://upload.libav.org
480 Did you provide a verbose summary about what the patch does change?
482 Did you provide a verbose explanation why it changes things like it does?
484 Did you provide a verbose summary of the user visible advantages and
485 disadvantages if the patch is applied?
487 Did you provide an example so we can verify the new feature added by the
490 If you added a new file, did you insert a license header? It should be
491 taken from Libav, not randomly copied and pasted from somewhere else.
493 You should maintain alphabetical order in alphabetically ordered lists as
494 long as doing so does not break API/ABI compatibility.
496 Lines with similar content should be aligned vertically when doing so
497 improves readability.
499 Make sure you check the return values of function and return appropriate
500 error codes. Especially memory allocation functions like @code{malloc()}
501 are notoriously left unchecked, which is a serious problem.
504 @section Patch review process
506 All patches posted to the
507 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
508 mailing list will be reviewed, unless they contain a
509 clear note that the patch is not for the git master branch.
510 Reviews and comments will be posted as replies to the patch on the
511 mailing list. The patch submitter then has to take care of every comment,
512 that can be by resubmitting a changed patch or by discussion. Resubmitted
513 patches will themselves be reviewed like any other patch. If at some point
514 a patch passes review with no comments then it is approved, that can for
515 simple and small patches happen immediately while large patches will generally
516 have to be changed and reviewed many times before they are approved.
517 After a patch is approved it will be committed to the repository.
519 We will review all submitted patches, but sometimes we are quite busy so
520 especially for large patches this can take several weeks.
522 When resubmitting patches, if their size grew or during the review different
523 issues arisen please split the patch so each issue has a specific patch.
525 @anchor{Regression Tests}
526 @section Regression Tests
528 Before submitting a patch (or committing to the repository), you should at
529 least make sure that it does not break anything.
531 If the code changed has already a test present in FATE you should run it,
532 otherwise it is advised to add it.
534 Improvements to codec or demuxer might change the FATE results. Make sure
535 to commit the update reference with the change and to explain in the comment
536 why the expected result changed.
538 Please refer to @url{fate.html}.