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{ffplay.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 libavcodec or libavformat in your program
28 You can integrate all the source code of the libraries to link them
29 statically to avoid any version problem. All you need is to provide a
30 'config.mak' and a 'config.h' in the parent directory. See the defines
31 generated by ./configure to understand what is needed.
33 You can use libavcodec or libavformat in your commercial program, but
34 @emph{any patch you make must be published}. The best way to proceed is
35 to send your patches to the FFmpeg mailing list.
39 There are 3 ways by which code gets into ffmpeg.
41 @item Submitting Patches to the main developer mailing list
42 see @ref{Submitting patches} for details.
43 @item Directly committing changes to the main tree.
44 @item Committing changes to a git clone, for example on github.com or
45 gitorious.org. And asking us to merge these changes.
48 Whichever way, changes should be reviewed by the maintainer of the code
49 before they are committed. And they should follow the @ref{Coding Rules}.
50 The developer making the commit and the author are responsible for their changes
51 and should try to fix issues their commit causes.
56 @subsection Code formatting conventions
58 There are the following guidelines regarding the indentation in files:
63 The TAB character is forbidden outside of Makefiles as is any
64 form of trailing whitespace. Commits containing either will be
65 rejected by the git repository.
67 You should try to limit your code lines to 80 characters; however, do so if
68 and only if this improves readability.
70 The presentation is one inspired by 'indent -i4 -kr -nut'.
72 The main priority in FFmpeg is simplicity and small code size in order to
73 minimize the bug count.
76 Use the JavaDoc/Doxygen format (see examples below) so that code documentation
77 can be generated automatically. All nontrivial functions should have a comment
78 above them explaining what the function does, even if it is just one sentence.
79 All structures and their member variables should be documented, too.
81 Avoid Qt-style and similar Doxygen syntax with @code{!} in it, i.e. replace
82 @code{//!} with @code{///} and similar. Also @@ syntax should be employed
83 for markup commands, i.e. use @code{@@param} and not @code{\param}.
97 typedef struct Foobar@{
98 int var1; /**< var1 description */
99 int var2; ///< var2 description
100 /** var3 description */
108 * @@param my_parameter description of my_parameter
109 * @@return return value description
111 int myfunc(int my_parameter)
115 @subsection C language features
117 FFmpeg is programmed in the ISO C90 language with a few additional
118 features from ISO C99, namely:
121 the @samp{inline} keyword;
125 designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
127 compound literals (@samp{x = (struct s) @{ 17, 23 @};})
130 These features are supported by all compilers we care about, so we will not
131 accept patches to remove their use unless they absolutely do not impair
132 clarity and performance.
134 All code must compile with recent versions of GCC and a number of other
135 currently supported compilers. To ensure compatibility, please do not use
136 additional C99 features or GCC extensions. Especially watch out for:
139 mixing statements and declarations;
141 @samp{long long} (use @samp{int64_t} instead);
143 @samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;
145 GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
148 @subsection Naming conventions
149 All names are using underscores (_), not CamelCase. For example, @samp{avfilter_get_video_buffer} is
150 a valid function name and @samp{AVFilterGetVideo} is not. The exception from this are type names, like
151 for example structs and enums; they should always be in the CamelCase
154 There are following conventions for naming variables and functions:
157 For local variables no prefix is required.
159 For variables and functions declared as @code{static} no prefixes are required.
161 For variables and functions used internally by the library, @code{ff_} prefix
163 For example, @samp{ff_w64_demuxer}.
165 For variables and functions used internally across multiple libraries, use
166 @code{avpriv_}. For example, @samp{avpriv_aac_parse_header}.
168 For exported names, each library has its own prefixes. Just check the existing
169 code and name accordingly.
172 @subsection Miscellanous conventions
175 fprintf and printf are forbidden in libavformat and libavcodec,
176 please use av_log() instead.
178 Casts should be used only when necessary. Unneeded parentheses
179 should also be avoided if they don't make the code easier to understand.
182 @subsection Editor configuration
183 In order to configure Vim to follow FFmpeg formatting conventions, paste
184 the following snippet into your @file{.vimrc}:
186 " indentation rules for FFmpeg: 4 spaces, no tabs
192 " allow tabs in Makefiles
193 autocmd FileType make set noexpandtab shiftwidth=8 softtabstop=8
194 " Trailing whitespace and tabs are forbidden, so highlight them.
195 highlight ForbiddenWhitespace ctermbg=red guibg=red
196 match ForbiddenWhitespace /\s\+$\|\t/
197 " Do not highlight spaces at the end of line while typing on that line.
198 autocmd InsertEnter * match ForbiddenWhitespace /\t\|\s\+\%#\@@<!$/
201 For Emacs, add these roughly equivalent lines to your @file{.emacs.d/init.el}:
203 (c-add-style "ffmpeg"
206 (indent-tabs-mode nil)
207 (show-trailing-whitespace t)
209 (statement-cont . (c-lineup-assignments +)))
212 (setq c-default-style "ffmpeg")
215 @section Development Policy
219 Contributions should be licensed under the LGPL 2.1, including an
220 "or any later version" clause, or the MIT license. GPL 2 including
221 an "or any later version" clause is also acceptable, but LGPL is
224 You must not commit code which breaks FFmpeg! (Meaning unfinished but
225 enabled code which breaks compilation or compiles but does not work or
226 breaks the regression tests)
227 You can commit unfinished stuff (for testing etc), but it must be disabled
228 (#ifdef etc) by default so it does not interfere with other developers'
231 You do not have to over-test things. If it works for you, and you think it
232 should work for others, then commit. If your code has problems
233 (portability, triggers compiler bugs, unusual environment etc) they will be
234 reported and eventually fixed.
236 Do not commit unrelated changes together, split them into self-contained
237 pieces. Also do not forget that if part B depends on part A, but A does not
238 depend on B, then A can and should be committed first and separate from B.
239 Keeping changes well split into self-contained parts makes reviewing and
240 understanding them on the commit log mailing list easier. This also helps
241 in case of debugging later on.
242 Also if you have doubts about splitting or not splitting, do not hesitate to
243 ask/discuss it on the developer mailing list.
245 Do not change behavior of the programs (renaming options etc) or public
246 API or ABI without first discussing it on the ffmpeg-devel mailing list.
247 Do not remove functionality from the code. Just improve!
249 Note: Redundant code can be removed.
251 Do not commit changes to the build system (Makefiles, configure script)
252 which change behavior, defaults etc, without asking first. The same
253 applies to compiler warning fixes, trivial looking fixes and to code
254 maintained by other developers. We usually have a reason for doing things
255 the way we do. Send your changes as patches to the ffmpeg-devel mailing
256 list, and if the code maintainers say OK, you may commit. This does not
257 apply to files you wrote and/or maintain.
259 We refuse source indentation and other cosmetic changes if they are mixed
260 with functional changes, such commits will be rejected and removed. Every
261 developer has his own indentation style, you should not change it. Of course
262 if you (re)write something, you can use your own style, even though we would
263 prefer if the indentation throughout FFmpeg was consistent (Many projects
264 force a given indentation style - we do not.). If you really need to make
265 indentation changes (try to avoid this), separate them strictly from real
268 NOTE: If you had to put if()@{ .. @} over a large (> 5 lines) chunk of code,
269 then either do NOT change the indentation of the inner part within (do not
270 move it to the right)! or do so in a separate commit
272 Always fill out the commit log message. Describe in a few lines what you
273 changed and why. You can refer to mailing list postings if you fix a
274 particular bug. Comments such as "fixed!" or "Changed it." are unacceptable.
276 area changed: Short 1 line description
278 details describing what and why and giving references.
280 Make sure the author of the commit is set correctly. (see git commit --author)
281 If you apply a patch, send an
282 answer to ffmpeg-devel (or wherever you got the patch from) saying that
283 you applied the patch.
285 When applying patches that have been discussed (at length) on the mailing
286 list, reference the thread in the log message.
288 Do NOT commit to code actively maintained by others without permission.
289 Send a patch to ffmpeg-devel instead. If no one answers within a reasonable
290 timeframe (12h for build failures and security fixes, 3 days small changes,
291 1 week for big patches) then commit your patch if you think it is OK.
292 Also note, the maintainer can simply ask for more time to review!
294 Subscribe to the ffmpeg-cvslog mailing list. The diffs of all commits
295 are sent there and reviewed by all the other developers. Bugs and possible
296 improvements or general questions regarding commits are discussed there. We
297 expect you to react if problems with your code are uncovered.
299 Update the documentation if you change behavior or add features. If you are
300 unsure how best to do this, send a patch to ffmpeg-devel, the documentation
301 maintainer(s) will review and commit your stuff.
303 Try to keep important discussions and requests (also) on the public
304 developer mailing list, so that all developers can benefit from them.
306 Never write to unallocated memory, never write over the end of arrays,
307 always check values read from some untrusted source before using them
308 as array index or other risky things.
310 Remember to check if you need to bump versions for the specific libav*
311 parts (libavutil, libavcodec, libavformat) you are changing. You need
312 to change the version integer.
313 Incrementing the first component means no backward compatibility to
314 previous versions (e.g. removal of a function from the public API).
315 Incrementing the second component means backward compatible change
316 (e.g. addition of a function to the public API or extension of an
317 existing data structure).
318 Incrementing the third component means a noteworthy binary compatible
319 change (e.g. encoder bug fix that matters for the decoder).
321 Compiler warnings indicate potential bugs or code with bad style. If a type of
322 warning always points to correct and clean code, that warning should
323 be disabled, not the code changed.
324 Thus the remaining warnings can either be bugs or correct code.
325 If it is a bug, the bug has to be fixed. If it is not, the code should
326 be changed to not generate a warning unless that causes a slowdown
327 or obfuscates the code.
329 If you add a new file, give it a proper license header. Do not copy and
330 paste it from a random place, use an existing file as template.
333 We think our rules are not too hard. If you have comments, contact us.
335 Note, these rules are mostly borrowed from the MPlayer project.
337 @anchor{Submitting patches}
338 @section Submitting patches
340 First, read the @ref{Coding Rules} above if you did not yet, in particular
341 the rules regarding patch submission.
343 When you submit your patch, please use @code{git format-patch} or
344 @code{git send-email}. We cannot read other diffs :-)
346 Also please do not submit a patch which contains several unrelated changes.
347 Split it into separate, self-contained pieces. This does not mean splitting
348 file by file. Instead, make the patch as small as possible while still
349 keeping it as a logical unit that contains an individual change, even
350 if it spans multiple files. This makes reviewing your patches much easier
351 for us and greatly increases your chances of getting your patch applied.
353 Use the patcheck tool of FFmpeg to check your patch.
354 The tool is located in the tools directory.
356 Run the @ref{Regression tests} before submitting a patch in order to verify
357 it does not cause unexpected problems.
359 Patches should be posted as base64 encoded attachments (or any other
360 encoding which ensures that the patch will not be trashed during
361 transmission) to the ffmpeg-devel mailing list, see
362 @url{http://lists.ffmpeg.org/mailman/listinfo/ffmpeg-devel}
364 It also helps quite a bit if you tell us what the patch does (for example
365 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
368 Also please if you send several patches, send each patch as a separate mail,
369 do not attach several unrelated patches to the same mail.
371 Your patch will be reviewed on the mailing list. You will likely be asked
372 to make some changes and are expected to send in an improved version that
373 incorporates the requests from the review. This process may go through
374 several iterations. Once your patch is deemed good enough, some developer
375 will pick it up and commit it to the official FFmpeg tree.
377 Give us a few days to react. But if some time passes without reaction,
378 send a reminder by email. Your patch should eventually be dealt with.
381 @section New codecs or formats checklist
385 Did you use av_cold for codec initialization and close functions?
387 Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
388 AVInputFormat/AVOutputFormat struct?
390 Did you bump the minor version number (and reset the micro version
391 number) in @file{libavcodec/version.h} or @file{libavformat/version.h}?
393 Did you register it in @file{allcodecs.c} or @file{allformats.c}?
395 Did you add the CodecID to @file{avcodec.h}?
397 If it has a fourCC, did you add it to @file{libavformat/riff.c},
398 even if it is only a decoder?
400 Did you add a rule to compile the appropriate files in the Makefile?
401 Remember to do this even if you're just adding a format to a file that is
402 already being compiled by some other rule, like a raw demuxer.
404 Did you add an entry to the table of supported formats or codecs in
405 @file{doc/general.texi}?
407 Did you add an entry in the Changelog?
409 If it depends on a parser or a library, did you add that dependency in
412 Did you @code{git add} the appropriate files before committing?
414 Did you make sure it compiles standalone, i.e. with
415 @code{configure --disable-everything --enable-decoder=foo}
416 (or @code{--enable-demuxer} or whatever your component is)?
420 @section patch submission checklist
424 Does @code{make fate} pass with the patch applied?
426 Was the patch generated with git format-patch or send-email?
428 Did you sign off your patch? (git commit -s)
429 See @url{http://kerneltrap.org/files/Jeremy/DCO.txt} for the meaning
432 Did you provide a clear git commit log message?
434 Is the patch against latest FFmpeg git master branch?
436 Are you subscribed to ffmpeg-devel?
437 (the list is subscribers only due to spam)
439 Have you checked that the changes are minimal, so that the same cannot be
440 achieved with a smaller patch and/or simpler final code?
442 If the change is to speed critical code, did you benchmark it?
444 If you did any benchmarks, did you provide them in the mail?
446 Have you checked that the patch does not introduce buffer overflows or
447 other security issues?
449 Did you test your decoder or demuxer against damaged data? If no, see
450 tools/trasher and the noise bitstream filter. Your decoder or demuxer
451 should not crash or end in a (near) infinite loop when fed damaged data.
453 Does the patch not mix functional and cosmetic changes?
455 Did you add tabs or trailing whitespace to the code? Both are forbidden.
457 Is the patch attached to the email you send?
459 Is the mime type of the patch correct? It should be text/x-diff or
460 text/x-patch or at least text/plain and not application/octet-stream.
462 If the patch fixes a bug, did you provide a verbose analysis of the bug?
464 If the patch fixes a bug, did you provide enough information, including
465 a sample, so the bug can be reproduced and the fix can be verified?
466 Note please do not attach samples >100k to mails but rather provide a
467 URL, you can upload to ftp://upload.ffmpeg.org
469 Did you provide a verbose summary about what the patch does change?
471 Did you provide a verbose explanation why it changes things like it does?
473 Did you provide a verbose summary of the user visible advantages and
474 disadvantages if the patch is applied?
476 Did you provide an example so we can verify the new feature added by the
479 If you added a new file, did you insert a license header? It should be
480 taken from FFmpeg, not randomly copied and pasted from somewhere else.
482 You should maintain alphabetical order in alphabetically ordered lists as
483 long as doing so does not break API/ABI compatibility.
485 Lines with similar content should be aligned vertically when doing so
486 improves readability.
488 Consider to add a regression test for your code.
490 If you added YASM code please check that things still work with --disable-yasm
493 @section Patch review process
495 All patches posted to ffmpeg-devel will be reviewed, unless they contain a
496 clear note that the patch is not for the git master branch.
497 Reviews and comments will be posted as replies to the patch on the
498 mailing list. The patch submitter then has to take care of every comment,
499 that can be by resubmitting a changed patch or by discussion. Resubmitted
500 patches will themselves be reviewed like any other patch. If at some point
501 a patch passes review with no comments then it is approved, that can for
502 simple and small patches happen immediately while large patches will generally
503 have to be changed and reviewed many times before they are approved.
504 After a patch is approved it will be committed to the repository.
506 We will review all submitted patches, but sometimes we are quite busy so
507 especially for large patches this can take several weeks.
509 If you feel that the review process is too slow and you are willing to try to
510 take over maintainership of the area of code you change then just clone
511 git master and maintain the area of code there. We will merge each area from
512 where its best maintained.
514 When resubmitting patches, please do not make any significant changes
515 not related to the comments received during review. Such patches will
516 be rejected. Instead, submit significant changes or new features as
519 @anchor{Regression tests}
520 @section Regression tests
522 Before submitting a patch (or committing to the repository), you should at least
523 test that you did not break anything.
525 Running 'make fate' accomplishes this, please see @url{fate.html} for details.
527 [Of course, some patches may change the results of the regression tests. In
528 this case, the reference results of the regression tests shall be modified