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 In case of a single-statement if, no curly braces are required:
82 Do not put spaces immediately inside parentheses. @samp{if (ret)} is
83 a valid style; @samp{if ( ret )} is not.
86 There are the following guidelines regarding the indentation in files:
91 The TAB character is forbidden outside of Makefiles as is any
92 form of trailing whitespace. Commits containing either will be
93 rejected by the git repository.
95 You should try to limit your code lines to 80 characters; however, do so if
96 and only if this improves readability.
98 The presentation is one inspired by 'indent -i4 -kr -nut'.
100 The main priority in Libav is simplicity and small code size in order to
101 minimize the bug count.
104 Use the JavaDoc/Doxygen format (see examples below) so that code documentation
105 can be generated automatically. All nontrivial functions should have a comment
106 above them explaining what the function does, even if it is just one sentence.
107 All structures and their member variables should be documented, too.
109 Avoid Qt-style and similar Doxygen syntax with @code{!} in it, i.e. replace
110 @code{//!} with @code{///} and similar. Also @@ syntax should be employed
111 for markup commands, i.e. use @code{@@param} and not @code{\param}.
125 typedef struct Foobar@{
126 int var1; /**< var1 description */
127 int var2; ///< var2 description
128 /** var3 description */
136 * @@param my_parameter description of my_parameter
137 * @@return return value description
139 int myfunc(int my_parameter)
143 @subsection C language features
145 Libav is programmed in the ISO C90 language with a few additional
146 features from ISO C99, namely:
149 the @samp{inline} keyword;
153 designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
155 compound literals (@samp{x = (struct s) @{ 17, 23 @};})
158 These features are supported by all compilers we care about, so we will not
159 accept patches to remove their use unless they absolutely do not impair
160 clarity and performance.
162 All code must compile with recent versions of GCC and a number of other
163 currently supported compilers. To ensure compatibility, please do not use
164 additional C99 features or GCC extensions. Especially watch out for:
167 mixing statements and declarations;
169 @samp{long long} (use @samp{int64_t} instead);
171 @samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;
173 GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
176 @subsection Naming conventions
177 All names are using underscores (_), not CamelCase. For example,
178 @samp{avfilter_get_video_buffer} is a valid function name and
179 @samp{AVFilterGetVideo} is not. The only exception from this are structure
180 names; they should always be in the CamelCase
182 There are following conventions for naming variables and functions:
185 For local variables no prefix is required.
187 For variables and functions declared as @code{static} no prefixes are required.
189 For variables and functions used internally by the library, @code{ff_} prefix
191 For example, @samp{ff_w64_demuxer}.
193 For variables and functions used internally across multiple libraries, use
194 @code{avpriv_}. For example, @samp{avpriv_aac_parse_header}.
196 For exported names, each library has its own prefixes. Just check the existing
197 code and name accordingly.
200 @subsection Miscellanous conventions
203 fprintf and printf are forbidden in libavformat and libavcodec,
204 please use av_log() instead.
206 Casts should be used only when necessary. Unneeded parentheses
207 should also be avoided if they don't make the code easier to understand.
210 @subsection Editor configuration
211 In order to configure Vim to follow Libav formatting conventions, paste
212 the following snippet into your @file{.vimrc}:
214 " indentation rules for libav: 4 spaces, no tabs
218 " allow tabs in Makefiles
219 autocmd FileType make set noexpandtab shiftwidth=8 softtabstop=8
220 " Trailing whitespace and tabs are forbidden, so highlight them.
221 highlight ForbiddenWhitespace ctermbg=red guibg=red
222 match ForbiddenWhitespace /\s\+$\|\t/
223 " Do not highlight spaces at the end of line while typing on that line.
224 autocmd InsertEnter * match ForbiddenWhitespace /\t\|\s\+\%#\@@<!$/
227 For Emacs, add these roughly equivalent lines to your @file{.emacs.d/init.el}:
229 (setq c-default-style "k&r")
230 (setq-default c-basic-offset 4)
231 (setq-default indent-tabs-mode nil)
232 (setq-default show-trailing-whitespace t)
235 @section Development Policy
239 Contributions should be licensed under the LGPL 2.1, including an
240 "or any later version" clause, or the MIT license. GPL 2 including
241 an "or any later version" clause is also acceptable, but LGPL is
244 All the patches MUST be reviewed in the mailing list before they are
247 The Libav coding style should remain consistent. Changes to
248 conform will be suggested during the review or implemented on commit.
250 Patches should be generated using @code{git format-patch} or directly sent
251 using @code{git send-email}.
252 Please make sure you give the proper credit by setting the correct author
255 The commit message should have a short first line in the form of
256 @samp{topic: short description} as header, separated by a newline
257 from the body consting in few lines explaining the reason of the patch.
258 Referring to the issue on the bug tracker does not exempt to report an
261 Work in progress patches should be sent to the mailing list with the [WIP]
264 Branches in public personal repos are advised as way to
265 work on issues collaboratively.
267 You do not have to over-test things. If it works for you and you think it
268 should work for others, send it to the mailing list for review.
269 If you have doubt about portability please state it in the submission so
270 people with specific hardware could test it.
272 Do not commit unrelated changes together, split them into self-contained
273 pieces. Also do not forget that if part B depends on part A, but A does not
274 depend on B, then A can and should be committed first and separate from B.
275 Keeping changes well split into self-contained parts makes reviewing and
276 understanding them on the commit log mailing list easier. This also helps
277 in case of debugging later on.
279 Patches that change behavior of the programs (renaming options etc) or
280 public API or ABI should be discussed in depth and possible few days should
281 pass between discussion and commit.
282 Changes to the build system (Makefiles, configure script) which alter
283 the expected behavior should be considered in the same regard.
285 When applying patches that have been discussed (at length) on the mailing
286 list, reference the thread in the log message.
289 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel} and
290 @uref{https://lists.libav.org/mailman/listinfo/libav-commits, libav-commits}
292 Bugs and possible improvements or general questions regarding commits
293 are discussed on libav-devel. We expect you to react if problems with
294 your code are uncovered.
296 Update the documentation if you change behavior or add features. If you are
297 unsure how best to do this, send an [RFC] patch to libav-devel.
299 All discussions and decisions should be reported on the public developer
300 mailing list, so that there is a reference to them.
301 Other media (e.g. IRC) should be used for coordination and immediate
304 Never write to unallocated memory, never write over the end of arrays,
305 always check values read from some untrusted source before using them
306 as array index or other risky things. Always use valgrind to doublecheck.
308 Remember to check if you need to bump versions for the specific libav
309 parts (libavutil, libavcodec, libavformat) you are changing. You need
310 to change the version integer.
311 Incrementing the first component means no backward compatibility to
312 previous versions (e.g. removal of a function from the public API).
313 Incrementing the second component means backward compatible change
314 (e.g. addition of a function to the public API or extension of an
315 existing data structure).
316 Incrementing the third component means a noteworthy binary compatible
317 change (e.g. encoder bug fix that matters for the decoder).
319 Compiler warnings indicate potential bugs or code with bad style.
320 If it is a bug, the bug has to be fixed. If it is not, the code should
321 be changed to not generate a warning unless that causes a slowdown
322 or obfuscates the code.
323 If a type of warning leads to too many false positives, that warning
324 should be disabled, not the code changed.
326 If you add a new file, give it a proper license header. Do not copy and
327 paste it from a random place, use an existing file as template.
330 We think our rules are not too hard. If you have comments, contact us.
332 Note, some rules were borrowed from the MPlayer project.
334 @section Submitting patches
336 First, read the @ref{Coding Rules} above if you did not yet, in particular
337 the rules regarding patch submission.
339 As stated already, please do not submit a patch which contains several
341 Split it into separate, self-contained pieces. This does not mean splitting
342 file by file. Instead, make the patch as small as possible while still
343 keeping it as a logical unit that contains an individual change, even
344 if it spans multiple files. This makes reviewing your patches much easier
345 for us and greatly increases your chances of getting your patch applied.
347 Use the patcheck tool of Libav to check your patch.
348 The tool is located in the tools directory.
350 Run the @ref{Regression Tests} before submitting a patch in order to verify
351 it does not cause unexpected problems.
353 Patches should be posted as base64 encoded attachments (or any other
354 encoding which ensures that the patch will not be trashed during
356 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
359 It also helps quite a bit if you tell us what the patch does (for example
360 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
361 and has no lrint()'). This kind of explanation should be the body of the
364 Also please if you send several patches, send each patch as a separate mail,
365 do not attach several unrelated patches to the same mail.
367 Use @code{git send-email} when possible since it will properly send patches
368 without requiring extra care.
370 Your patch will be reviewed on the mailing list. You will likely be asked
371 to make some changes and are expected to send in an improved version that
372 incorporates the requests from the review. This process may go through
373 several iterations. Once your patch is deemed good enough, it will be
374 committed to the official Libav tree.
376 Give us a few days to react. But if some time passes without reaction,
377 send a reminder by email. Your patch should eventually be dealt with.
380 @section New codecs or formats checklist
384 Did you use av_cold for codec initialization and close functions?
386 Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
387 AVInputFormat/AVOutputFormat struct?
389 Did you bump the minor version number (and reset the micro version
390 number) in @file{libavcodec/version.h} or @file{libavformat/version.h}?
392 Did you register it in @file{allcodecs.c} or @file{allformats.c}?
394 Did you add the CodecID to @file{avcodec.h}?
396 If it has a fourcc, did you add it to @file{libavformat/riff.c},
397 even if it is only a decoder?
399 Did you add a rule to compile the appropriate files in the Makefile?
400 Remember to do this even if you are just adding a format to a file that
401 is already being compiled by some other rule, like a raw demuxer.
403 Did you add an entry to the table of supported formats or codecs in
404 @file{doc/general.texi}?
406 Did you add an entry in the Changelog?
408 If it depends on a parser or a library, did you add that dependency in
411 Did you @code{git add} the appropriate files before committing?
413 Did you make sure it compiles standalone, i.e. with
414 @code{configure --disable-everything --enable-decoder=foo}
415 (or @code{--enable-demuxer} or whatever your component is)?
419 @section patch submission checklist
423 Does @code{make fate} pass with the patch applied?
425 Does @code{make checkheaders} pass with the patch applied?
427 Is the patch against latest Libav git master branch?
429 Are you subscribed to the
430 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
431 mailing list? (Only list subscribers are allowed to post.)
433 Have you checked that the changes are minimal, so that the same cannot be
434 achieved with a smaller patch and/or simpler final code?
436 If the change is to speed critical code, did you benchmark it?
438 If you did any benchmarks, did you provide them in the mail?
440 Have you checked that the patch does not introduce buffer overflows or
441 other security issues?
443 Did you test your decoder or demuxer against damaged data? If no, see
444 tools/trasher and the noise bitstream filter. Your decoder or demuxer
445 should not crash or end in a (near) infinite loop when fed damaged data.
447 Does the patch not mix functional and cosmetic changes?
449 Did you add tabs or trailing whitespace to the code? Both are forbidden.
451 Is the patch attached to the email you send?
453 Is the mime type of the patch correct? It should be text/x-diff or
454 text/x-patch or at least text/plain and not application/octet-stream.
456 If the patch fixes a bug, did you provide a verbose analysis of the bug?
458 If the patch fixes a bug, did you provide enough information, including
459 a sample, so the bug can be reproduced and the fix can be verified?
460 Note please do not attach samples >100k to mails but rather provide a
461 URL, you can upload to ftp://upload.libav.org
463 Did you provide a verbose summary about what the patch does change?
465 Did you provide a verbose explanation why it changes things like it does?
467 Did you provide a verbose summary of the user visible advantages and
468 disadvantages if the patch is applied?
470 Did you provide an example so we can verify the new feature added by the
473 If you added a new file, did you insert a license header? It should be
474 taken from Libav, not randomly copied and pasted from somewhere else.
476 You should maintain alphabetical order in alphabetically ordered lists as
477 long as doing so does not break API/ABI compatibility.
479 Lines with similar content should be aligned vertically when doing so
480 improves readability.
483 @section Patch review process
485 All patches posted to the
486 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
487 mailing list will be reviewed, unless they contain a
488 clear note that the patch is not for the git master branch.
489 Reviews and comments will be posted as replies to the patch on the
490 mailing list. The patch submitter then has to take care of every comment,
491 that can be by resubmitting a changed patch or by discussion. Resubmitted
492 patches will themselves be reviewed like any other patch. If at some point
493 a patch passes review with no comments then it is approved, that can for
494 simple and small patches happen immediately while large patches will generally
495 have to be changed and reviewed many times before they are approved.
496 After a patch is approved it will be committed to the repository.
498 We will review all submitted patches, but sometimes we are quite busy so
499 especially for large patches this can take several weeks.
501 When resubmitting patches, if their size grew or during the review different
502 issues arisen please split the patch so each issue has a specific patch.
504 @anchor{Regression Tests}
505 @section Regression Tests
507 Before submitting a patch (or committing to the repository), you should at
508 least make sure that it does not break anything.
510 If the code changed has already a test present in FATE you should run it,
511 otherwise it is advised to add it.
513 Improvements to codec or demuxer might change the FATE results. Make sure
514 to commit the update reference with the change and to explain in the comment
515 why the expected result changed.
517 Please refer to @url{fate.html}.