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 betwen the statement and parenthesis
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 parenthesis. @samp{if (ret)} is a valid style; @samp{if ( ret )} is not.
85 There are the following guidelines regarding the indentation in files:
90 The TAB character is forbidden outside of Makefiles as is any
91 form of trailing whitespace. Commits containing either will be
92 rejected by the git repository.
94 You should try to limit your code lines to 80 characters; however, do so if and only if this improves readability.
96 The presentation is one inspired by 'indent -i4 -kr -nut'.
98 The main priority in Libav is simplicity and small code size in order to
99 minimize the bug count.
102 Use the JavaDoc/Doxygen format (see examples below) so that code documentation
103 can be generated automatically. All nontrivial functions should have a comment
104 above them explaining what the function does, even if it is just one sentence.
105 All structures and their member variables should be documented, too.
118 typedef struct Foobar@{
119 int var1; /**< var1 description */
120 int var2; ///< var2 description
121 /** var3 description */
129 * @@param my_parameter description of my_parameter
130 * @@return return value description
132 int myfunc(int my_parameter)
136 @subsection C language features
138 Libav is programmed in the ISO C90 language with a few additional
139 features from ISO C99, namely:
142 the @samp{inline} keyword;
146 designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
148 compound literals (@samp{x = (struct s) @{ 17, 23 @};})
151 These features are supported by all compilers we care about, so we will not
152 accept patches to remove their use unless they absolutely do not impair
153 clarity and performance.
155 All code must compile with recent versions of GCC and a number of other
156 currently supported compilers. To ensure compatibility, please do not use
157 additional C99 features or GCC extensions. Especially watch out for:
160 mixing statements and declarations;
162 @samp{long long} (use @samp{int64_t} instead);
164 @samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;
166 GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
169 @subsection Naming conventions
170 All names are using underscores (_), not CamelCase. For example, @samp{avfilter_get_video_buffer} is
171 a valid function name and @samp{AVFilterGetVideo} is not. The only exception from this are structure names;
172 they should always be in the CamelCase
174 There are following conventions for naming variables and functions:
177 For local variables no prefix is required.
179 For variables and functions declared as @code{static} no prefixes are required.
181 For variables and functions used internally by the library, @code{ff_} prefix should be used.
182 For example, @samp{ff_w64_demuxer}.
184 For variables and functions used internally across multiple libraries, use @code{avpriv_}. For example,
185 @samp{avpriv_aac_parse_header}.
187 For exported names, each library has its own prefixes. Just check the existing code and name accordingly.
190 @subsection Miscellanous conventions
193 fprintf and printf are forbidden in libavformat and libavcodec,
194 please use av_log() instead.
196 Casts should be used only when necessary. Unneeded parentheses
197 should also be avoided if they don't make the code easier to understand.
200 @section Development Policy
204 Contributions should be licensed under the LGPL 2.1, including an
205 "or any later version" clause, or the MIT license. GPL 2 including
206 an "or any later version" clause is also acceptable, but LGPL is
209 All the patches MUST be reviewed in the mailing list before they are
212 The Libav coding style should remain consistent. Changes to
213 conform will be suggested during the review or implemented on commit.
215 Patches should be generated using @code{git format-patch} or directly sent
216 using @code{git send-email}.
217 Please make sure you give the proper credit by setting the correct author
220 The commit message should have a short first line in the form of
221 @samp{topic: short description} as header, separated by a newline
222 from the body consting in few lines explaining the reason of the patch.
223 Referring to the issue on the bug tracker does not exempt to report an
226 Work in progress patches should be sent to the mailing list with the [WIP]
229 Branches in public personal repos are advised as way to
230 work on issues collaboratively.
232 You do not have to over-test things. If it works for you and you think it
233 should work for others, send it to the mailing list for review.
234 If you have doubt about portability please state it in the submission so
235 people with specific hardware could test it.
237 Do not commit unrelated changes together, split them into self-contained
238 pieces. Also do not forget that if part B depends on part A, but A does not
239 depend on B, then A can and should be committed first and separate from B.
240 Keeping changes well split into self-contained parts makes reviewing and
241 understanding them on the commit log mailing list easier. This also helps
242 in case of debugging later on.
244 Patches that change behavior of the programs (renaming options etc) or
245 public API or ABI should be discussed in depth and possible few days should
246 pass between discussion and commit.
247 Changes to the build system (Makefiles, configure script) which alter
248 the expected behavior should be considered in the same regard.
250 When applying patches that have been discussed (at length) on the mailing
251 list, reference the thread in the log message.
254 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel} and
255 @uref{https://lists.libav.org/mailman/listinfo/libav-commits, libav-commits}
257 Bugs and possible improvements or general questions regarding commits
258 are discussed on libav-devel. We expect you to react if problems with
259 your code are uncovered.
261 Update the documentation if you change behavior or add features. If you are
262 unsure how best to do this, send an [RFC] patch to libav-devel.
264 All discussions and decisions should be reported on the public developer
265 mailing list, so that there is a reference to them.
266 Other media (e.g. IRC) should be used for coordination and immediate
269 Never write to unallocated memory, never write over the end of arrays,
270 always check values read from some untrusted source before using them
271 as array index or other risky things. Always use valgrind to doublecheck.
273 Remember to check if you need to bump versions for the specific libav
274 parts (libavutil, libavcodec, libavformat) you are changing. You need
275 to change the version integer.
276 Incrementing the first component means no backward compatibility to
277 previous versions (e.g. removal of a function from the public API).
278 Incrementing the second component means backward compatible change
279 (e.g. addition of a function to the public API or extension of an
280 existing data structure).
281 Incrementing the third component means a noteworthy binary compatible
282 change (e.g. encoder bug fix that matters for the decoder).
284 Compiler warnings indicate potential bugs or code with bad style.
285 If it is a bug, the bug has to be fixed. If it is not, the code should
286 be changed to not generate a warning unless that causes a slowdown
287 or obfuscates the code.
288 If a type of warning leads to too many false positives, that warning
289 should be disabled, not the code changed.
291 If you add a new file, give it a proper license header. Do not copy and
292 paste it from a random place, use an existing file as template.
295 We think our rules are not too hard. If you have comments, contact us.
297 Note, some rules were borrowed from the MPlayer project.
299 @section Submitting patches
301 First, read the @ref{Coding Rules} above if you did not yet, in particular
302 the rules regarding patch submission.
304 As stated already, please do not submit a patch which contains several
306 Split it into separate, self-contained pieces. This does not mean splitting
307 file by file. Instead, make the patch as small as possible while still
308 keeping it as a logical unit that contains an individual change, even
309 if it spans multiple files. This makes reviewing your patches much easier
310 for us and greatly increases your chances of getting your patch applied.
312 Use the patcheck tool of Libav to check your patch.
313 The tool is located in the tools directory.
315 Run the @ref{Regression Tests} before submitting a patch in order to verify
316 it does not cause unexpected problems.
318 Patches should be posted as base64 encoded attachments (or any other
319 encoding which ensures that the patch will not be trashed during
321 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
324 It also helps quite a bit if you tell us what the patch does (for example
325 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
326 and has no lrint()'). This kind of explanation should be the body of the
329 Also please if you send several patches, send each patch as a separate mail,
330 do not attach several unrelated patches to the same mail.
332 Use @code{git send-email} when possible since it will properly send patches
333 without requiring extra care.
335 Your patch will be reviewed on the mailing list. You will likely be asked
336 to make some changes and are expected to send in an improved version that
337 incorporates the requests from the review. This process may go through
338 several iterations. Once your patch is deemed good enough, it will be
339 committed to the official Libav tree.
341 Give us a few days to react. But if some time passes without reaction,
342 send a reminder by email. Your patch should eventually be dealt with.
345 @section New codecs or formats checklist
349 Did you use av_cold for codec initialization and close functions?
351 Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
352 AVInputFormat/AVOutputFormat struct?
354 Did you bump the minor version number (and reset the micro version
355 number) in @file{libavcodec/version.h} or @file{libavformat/version.h}?
357 Did you register it in @file{allcodecs.c} or @file{allformats.c}?
359 Did you add the CodecID to @file{avcodec.h}?
361 If it has a fourcc, did you add it to @file{libavformat/riff.c},
362 even if it is only a decoder?
364 Did you add a rule to compile the appropriate files in the Makefile?
365 Remember to do this even if you are just adding a format to a file that
366 is already being compiled by some other rule, like a raw demuxer.
368 Did you add an entry to the table of supported formats or codecs in
369 @file{doc/general.texi}?
371 Did you add an entry in the Changelog?
373 If it depends on a parser or a library, did you add that dependency in
376 Did you @code{git add} the appropriate files before committing?
378 Did you make sure it compiles standalone, i.e. with
379 @code{configure --disable-everything --enable-decoder=foo}
380 (or @code{--enable-demuxer} or whatever your component is)?
384 @section patch submission checklist
388 Does @code{make fate} pass with the patch applied?
390 Does @code{make checkheaders} pass with the patch applied?
392 Is the patch against latest Libav git master branch?
394 Are you subscribed to the
395 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
396 mailing list? (Only list subscribers are allowed to post.)
398 Have you checked that the changes are minimal, so that the same cannot be
399 achieved with a smaller patch and/or simpler final code?
401 If the change is to speed critical code, did you benchmark it?
403 If you did any benchmarks, did you provide them in the mail?
405 Have you checked that the patch does not introduce buffer overflows or
406 other security issues?
408 Did you test your decoder or demuxer against damaged data? If no, see
409 tools/trasher and the noise bitstream filter. Your decoder or demuxer
410 should not crash or end in a (near) infinite loop when fed damaged data.
412 Does the patch not mix functional and cosmetic changes?
414 Did you add tabs or trailing whitespace to the code? Both are forbidden.
416 Is the patch attached to the email you send?
418 Is the mime type of the patch correct? It should be text/x-diff or
419 text/x-patch or at least text/plain and not application/octet-stream.
421 If the patch fixes a bug, did you provide a verbose analysis of the bug?
423 If the patch fixes a bug, did you provide enough information, including
424 a sample, so the bug can be reproduced and the fix can be verified?
425 Note please do not attach samples >100k to mails but rather provide a
426 URL, you can upload to ftp://upload.libav.org
428 Did you provide a verbose summary about what the patch does change?
430 Did you provide a verbose explanation why it changes things like it does?
432 Did you provide a verbose summary of the user visible advantages and
433 disadvantages if the patch is applied?
435 Did you provide an example so we can verify the new feature added by the
438 If you added a new file, did you insert a license header? It should be
439 taken from Libav, not randomly copied and pasted from somewhere else.
441 You should maintain alphabetical order in alphabetically ordered lists as
442 long as doing so does not break API/ABI compatibility.
444 Lines with similar content should be aligned vertically when doing so
445 improves readability.
448 @section Patch review process
450 All patches posted to the
451 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
452 mailing list will be reviewed, unless they contain a
453 clear note that the patch is not for the git master branch.
454 Reviews and comments will be posted as replies to the patch on the
455 mailing list. The patch submitter then has to take care of every comment,
456 that can be by resubmitting a changed patch or by discussion. Resubmitted
457 patches will themselves be reviewed like any other patch. If at some point
458 a patch passes review with no comments then it is approved, that can for
459 simple and small patches happen immediately while large patches will generally
460 have to be changed and reviewed many times before they are approved.
461 After a patch is approved it will be committed to the repository.
463 We will review all submitted patches, but sometimes we are quite busy so
464 especially for large patches this can take several weeks.
466 When resubmitting patches, if their size grew or during the review different
467 issues arisen please split the patch so each issue has a specific patch.
469 @anchor{Regression Tests}
470 @section Regression Tests
472 Before submitting a patch (or committing to the repository), you should at
473 least make sure that it does not break anything.
475 If the code changed has already a test present in FATE you should run it,
476 otherwise it is advised to add it.
478 Improvements to codec or demuxer might change the FATE results. Make sure
479 to commit the update reference with the change and to explain in the comment
480 why the expected result changed.
482 Please refer to @file{doc/fate.txt}.