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
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 parenthesis. @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.
120 typedef struct Foobar@{
121 int var1; /**< var1 description */
122 int var2; ///< var2 description
123 /** var3 description */
131 * @@param my_parameter description of my_parameter
132 * @@return return value description
134 int myfunc(int my_parameter)
138 @subsection C language features
140 Libav is programmed in the ISO C90 language with a few additional
141 features from ISO C99, namely:
144 the @samp{inline} keyword;
148 designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
150 compound literals (@samp{x = (struct s) @{ 17, 23 @};})
153 These features are supported by all compilers we care about, so we will not
154 accept patches to remove their use unless they absolutely do not impair
155 clarity and performance.
157 All code must compile with recent versions of GCC and a number of other
158 currently supported compilers. To ensure compatibility, please do not use
159 additional C99 features or GCC extensions. Especially watch out for:
162 mixing statements and declarations;
164 @samp{long long} (use @samp{int64_t} instead);
166 @samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;
168 GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
171 @subsection Naming conventions
172 All names are using underscores (_), not CamelCase. For example,
173 @samp{avfilter_get_video_buffer} is a valid function name and
174 @samp{AVFilterGetVideo} is not. The only exception from this are structure
175 names; they should always be in the CamelCase
177 There are following conventions for naming variables and functions:
180 For local variables no prefix is required.
182 For variables and functions declared as @code{static} no prefixes are required.
184 For variables and functions used internally by the library, @code{ff_} prefix
186 For example, @samp{ff_w64_demuxer}.
188 For variables and functions used internally across multiple libraries, use
189 @code{avpriv_}. For example, @samp{avpriv_aac_parse_header}.
191 For exported names, each library has its own prefixes. Just check the existing
192 code and name accordingly.
195 @subsection Miscellanous conventions
198 fprintf and printf are forbidden in libavformat and libavcodec,
199 please use av_log() instead.
201 Casts should be used only when necessary. Unneeded parentheses
202 should also be avoided if they don't make the code easier to understand.
205 @section Development Policy
209 Contributions should be licensed under the LGPL 2.1, including an
210 "or any later version" clause, or the MIT license. GPL 2 including
211 an "or any later version" clause is also acceptable, but LGPL is
214 All the patches MUST be reviewed in the mailing list before they are
217 The Libav coding style should remain consistent. Changes to
218 conform will be suggested during the review or implemented on commit.
220 Patches should be generated using @code{git format-patch} or directly sent
221 using @code{git send-email}.
222 Please make sure you give the proper credit by setting the correct author
225 The commit message should have a short first line in the form of
226 @samp{topic: short description} as header, separated by a newline
227 from the body consting in few lines explaining the reason of the patch.
228 Referring to the issue on the bug tracker does not exempt to report an
231 Work in progress patches should be sent to the mailing list with the [WIP]
234 Branches in public personal repos are advised as way to
235 work on issues collaboratively.
237 You do not have to over-test things. If it works for you and you think it
238 should work for others, send it to the mailing list for review.
239 If you have doubt about portability please state it in the submission so
240 people with specific hardware could test it.
242 Do not commit unrelated changes together, split them into self-contained
243 pieces. Also do not forget that if part B depends on part A, but A does not
244 depend on B, then A can and should be committed first and separate from B.
245 Keeping changes well split into self-contained parts makes reviewing and
246 understanding them on the commit log mailing list easier. This also helps
247 in case of debugging later on.
249 Patches that change behavior of the programs (renaming options etc) or
250 public API or ABI should be discussed in depth and possible few days should
251 pass between discussion and commit.
252 Changes to the build system (Makefiles, configure script) which alter
253 the expected behavior should be considered in the same regard.
255 When applying patches that have been discussed (at length) on the mailing
256 list, reference the thread in the log message.
259 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel} and
260 @uref{https://lists.libav.org/mailman/listinfo/libav-commits, libav-commits}
262 Bugs and possible improvements or general questions regarding commits
263 are discussed on libav-devel. We expect you to react if problems with
264 your code are uncovered.
266 Update the documentation if you change behavior or add features. If you are
267 unsure how best to do this, send an [RFC] patch to libav-devel.
269 All discussions and decisions should be reported on the public developer
270 mailing list, so that there is a reference to them.
271 Other media (e.g. IRC) should be used for coordination and immediate
274 Never write to unallocated memory, never write over the end of arrays,
275 always check values read from some untrusted source before using them
276 as array index or other risky things. Always use valgrind to doublecheck.
278 Remember to check if you need to bump versions for the specific libav
279 parts (libavutil, libavcodec, libavformat) you are changing. You need
280 to change the version integer.
281 Incrementing the first component means no backward compatibility to
282 previous versions (e.g. removal of a function from the public API).
283 Incrementing the second component means backward compatible change
284 (e.g. addition of a function to the public API or extension of an
285 existing data structure).
286 Incrementing the third component means a noteworthy binary compatible
287 change (e.g. encoder bug fix that matters for the decoder).
289 Compiler warnings indicate potential bugs or code with bad style.
290 If it is a bug, the bug has to be fixed. If it is not, the code should
291 be changed to not generate a warning unless that causes a slowdown
292 or obfuscates the code.
293 If a type of warning leads to too many false positives, that warning
294 should be disabled, not the code changed.
296 If you add a new file, give it a proper license header. Do not copy and
297 paste it from a random place, use an existing file as template.
300 We think our rules are not too hard. If you have comments, contact us.
302 Note, some rules were borrowed from the MPlayer project.
304 @section Submitting patches
306 First, read the @ref{Coding Rules} above if you did not yet, in particular
307 the rules regarding patch submission.
309 As stated already, please do not submit a patch which contains several
311 Split it into separate, self-contained pieces. This does not mean splitting
312 file by file. Instead, make the patch as small as possible while still
313 keeping it as a logical unit that contains an individual change, even
314 if it spans multiple files. This makes reviewing your patches much easier
315 for us and greatly increases your chances of getting your patch applied.
317 Use the patcheck tool of Libav to check your patch.
318 The tool is located in the tools directory.
320 Run the @ref{Regression Tests} before submitting a patch in order to verify
321 it does not cause unexpected problems.
323 Patches should be posted as base64 encoded attachments (or any other
324 encoding which ensures that the patch will not be trashed during
326 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
329 It also helps quite a bit if you tell us what the patch does (for example
330 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
331 and has no lrint()'). This kind of explanation should be the body of the
334 Also please if you send several patches, send each patch as a separate mail,
335 do not attach several unrelated patches to the same mail.
337 Use @code{git send-email} when possible since it will properly send patches
338 without requiring extra care.
340 Your patch will be reviewed on the mailing list. You will likely be asked
341 to make some changes and are expected to send in an improved version that
342 incorporates the requests from the review. This process may go through
343 several iterations. Once your patch is deemed good enough, it will be
344 committed to the official Libav tree.
346 Give us a few days to react. But if some time passes without reaction,
347 send a reminder by email. Your patch should eventually be dealt with.
350 @section New codecs or formats checklist
354 Did you use av_cold for codec initialization and close functions?
356 Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
357 AVInputFormat/AVOutputFormat struct?
359 Did you bump the minor version number (and reset the micro version
360 number) in @file{libavcodec/version.h} or @file{libavformat/version.h}?
362 Did you register it in @file{allcodecs.c} or @file{allformats.c}?
364 Did you add the CodecID to @file{avcodec.h}?
366 If it has a fourcc, did you add it to @file{libavformat/riff.c},
367 even if it is only a decoder?
369 Did you add a rule to compile the appropriate files in the Makefile?
370 Remember to do this even if you are just adding a format to a file that
371 is already being compiled by some other rule, like a raw demuxer.
373 Did you add an entry to the table of supported formats or codecs in
374 @file{doc/general.texi}?
376 Did you add an entry in the Changelog?
378 If it depends on a parser or a library, did you add that dependency in
381 Did you @code{git add} the appropriate files before committing?
383 Did you make sure it compiles standalone, i.e. with
384 @code{configure --disable-everything --enable-decoder=foo}
385 (or @code{--enable-demuxer} or whatever your component is)?
389 @section patch submission checklist
393 Does @code{make fate} pass with the patch applied?
395 Does @code{make checkheaders} pass with the patch applied?
397 Is the patch against latest Libav git master branch?
399 Are you subscribed to the
400 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
401 mailing list? (Only list subscribers are allowed to post.)
403 Have you checked that the changes are minimal, so that the same cannot be
404 achieved with a smaller patch and/or simpler final code?
406 If the change is to speed critical code, did you benchmark it?
408 If you did any benchmarks, did you provide them in the mail?
410 Have you checked that the patch does not introduce buffer overflows or
411 other security issues?
413 Did you test your decoder or demuxer against damaged data? If no, see
414 tools/trasher and the noise bitstream filter. Your decoder or demuxer
415 should not crash or end in a (near) infinite loop when fed damaged data.
417 Does the patch not mix functional and cosmetic changes?
419 Did you add tabs or trailing whitespace to the code? Both are forbidden.
421 Is the patch attached to the email you send?
423 Is the mime type of the patch correct? It should be text/x-diff or
424 text/x-patch or at least text/plain and not application/octet-stream.
426 If the patch fixes a bug, did you provide a verbose analysis of the bug?
428 If the patch fixes a bug, did you provide enough information, including
429 a sample, so the bug can be reproduced and the fix can be verified?
430 Note please do not attach samples >100k to mails but rather provide a
431 URL, you can upload to ftp://upload.libav.org
433 Did you provide a verbose summary about what the patch does change?
435 Did you provide a verbose explanation why it changes things like it does?
437 Did you provide a verbose summary of the user visible advantages and
438 disadvantages if the patch is applied?
440 Did you provide an example so we can verify the new feature added by the
443 If you added a new file, did you insert a license header? It should be
444 taken from Libav, not randomly copied and pasted from somewhere else.
446 You should maintain alphabetical order in alphabetically ordered lists as
447 long as doing so does not break API/ABI compatibility.
449 Lines with similar content should be aligned vertically when doing so
450 improves readability.
453 @section Patch review process
455 All patches posted to the
456 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
457 mailing list will be reviewed, unless they contain a
458 clear note that the patch is not for the git master branch.
459 Reviews and comments will be posted as replies to the patch on the
460 mailing list. The patch submitter then has to take care of every comment,
461 that can be by resubmitting a changed patch or by discussion. Resubmitted
462 patches will themselves be reviewed like any other patch. If at some point
463 a patch passes review with no comments then it is approved, that can for
464 simple and small patches happen immediately while large patches will generally
465 have to be changed and reviewed many times before they are approved.
466 After a patch is approved it will be committed to the repository.
468 We will review all submitted patches, but sometimes we are quite busy so
469 especially for large patches this can take several weeks.
471 When resubmitting patches, if their size grew or during the review different
472 issues arisen please split the patch so each issue has a specific patch.
474 @anchor{Regression Tests}
475 @section Regression Tests
477 Before submitting a patch (or committing to the repository), you should at
478 least make sure that it does not break anything.
480 If the code changed has already a test present in FATE you should run it,
481 otherwise it is advised to add it.
483 Improvements to codec or demuxer might change the FATE results. Make sure
484 to commit the update reference with the change and to explain in the comment
485 why the expected result changed.
487 Please refer to @file{doc/fate.txt}.