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 and only if this improves readability.
69 The presentation is one inspired by 'indent -i4 -kr -nut'.
71 The main priority in FFmpeg is simplicity and small code size in order to
72 minimize the bug count.
75 Use the JavaDoc/Doxygen format (see examples below) so that code documentation
76 can be generated automatically. All nontrivial functions should have a comment
77 above them explaining what the function does, even if it is just one sentence.
78 All structures and their member variables should be documented, too.
91 typedef struct Foobar@{
92 int var1; /**< var1 description */
93 int var2; ///< var2 description
94 /** var3 description */
102 * @@param my_parameter description of my_parameter
103 * @@return return value description
105 int myfunc(int my_parameter)
109 @subsection C language features
111 FFmpeg is programmed in the ISO C90 language with a few additional
112 features from ISO C99, namely:
115 the @samp{inline} keyword;
119 designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
121 compound literals (@samp{x = (struct s) @{ 17, 23 @};})
124 These features are supported by all compilers we care about, so we will not
125 accept patches to remove their use unless they absolutely do not impair
126 clarity and performance.
128 All code must compile with recent versions of GCC and a number of other
129 currently supported compilers. To ensure compatibility, please do not use
130 additional C99 features or GCC extensions. Especially watch out for:
133 mixing statements and declarations;
135 @samp{long long} (use @samp{int64_t} instead);
137 @samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;
139 GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
142 @subsection Naming conventions
143 All names are using underscores (_), not CamelCase. For example, @samp{avfilter_get_video_buffer} is
144 a valid function name and @samp{AVFilterGetVideo} is not. The only exception from this are structure names;
145 they should always be in the CamelCase
147 There are following conventions for naming variables and functions:
150 For local variables no prefix is required.
152 For variables and functions declared as @code{static} no prefixes are required.
154 For variables and functions used internally by the library, @code{ff_} prefix should be used.
155 For example, @samp{ff_w64_demuxer}.
157 For variables and functions used internally across multiple libraries, use @code{avpriv_}. For example,
158 @samp{avpriv_aac_parse_header}.
160 For exported names, each library has its own prefixes. Just check the existing code and name accordingly.
163 @subsection Miscellanous conventions
166 fprintf and printf are forbidden in libavformat and libavcodec,
167 please use av_log() instead.
169 Casts should be used only when necessary. Unneeded parentheses
170 should also be avoided if they don't make the code easier to understand.
173 @section Development Policy
177 Contributions should be licensed under the LGPL 2.1, including an
178 "or any later version" clause, or the MIT license. GPL 2 including
179 an "or any later version" clause is also acceptable, but LGPL is
182 You must not commit code which breaks FFmpeg! (Meaning unfinished but
183 enabled code which breaks compilation or compiles but does not work or
184 breaks the regression tests)
185 You can commit unfinished stuff (for testing etc), but it must be disabled
186 (#ifdef etc) by default so it does not interfere with other developers'
189 You do not have to over-test things. If it works for you, and you think it
190 should work for others, then commit. If your code has problems
191 (portability, triggers compiler bugs, unusual environment etc) they will be
192 reported and eventually fixed.
194 Do not commit unrelated changes together, split them into self-contained
195 pieces. Also do not forget that if part B depends on part A, but A does not
196 depend on B, then A can and should be committed first and separate from B.
197 Keeping changes well split into self-contained parts makes reviewing and
198 understanding them on the commit log mailing list easier. This also helps
199 in case of debugging later on.
200 Also if you have doubts about splitting or not splitting, do not hesitate to
201 ask/discuss it on the developer mailing list.
203 Do not change behavior of the programs (renaming options etc) or public
204 API or ABI without first discussing it on the ffmpeg-devel mailing list.
205 Do not remove functionality from the code. Just improve!
207 Note: Redundant code can be removed.
209 Do not commit changes to the build system (Makefiles, configure script)
210 which change behavior, defaults etc, without asking first. The same
211 applies to compiler warning fixes, trivial looking fixes and to code
212 maintained by other developers. We usually have a reason for doing things
213 the way we do. Send your changes as patches to the ffmpeg-devel mailing
214 list, and if the code maintainers say OK, you may commit. This does not
215 apply to files you wrote and/or maintain.
217 We refuse source indentation and other cosmetic changes if they are mixed
218 with functional changes, such commits will be rejected and removed. Every
219 developer has his own indentation style, you should not change it. Of course
220 if you (re)write something, you can use your own style, even though we would
221 prefer if the indentation throughout FFmpeg was consistent (Many projects
222 force a given indentation style - we do not.). If you really need to make
223 indentation changes (try to avoid this), separate them strictly from real
226 NOTE: If you had to put if()@{ .. @} over a large (> 5 lines) chunk of code,
227 then either do NOT change the indentation of the inner part within (do not
228 move it to the right)! or do so in a separate commit
230 Always fill out the commit log message. Describe in a few lines what you
231 changed and why. You can refer to mailing list postings if you fix a
232 particular bug. Comments such as "fixed!" or "Changed it." are unacceptable.
234 area changed: Short 1 line description
236 details describing what and why and giving references.
238 Make sure the author of the commit is set correctly. (see git commit --author)
239 If you apply a patch, send an
240 answer to ffmpeg-devel (or wherever you got the patch from) saying that
241 you applied the patch.
243 When applying patches that have been discussed (at length) on the mailing
244 list, reference the thread in the log message.
246 Do NOT commit to code actively maintained by others without permission.
247 Send a patch to ffmpeg-devel instead. If no one answers within a reasonable
248 timeframe (12h for build failures and security fixes, 3 days small changes,
249 1 week for big patches) then commit your patch if you think it is OK.
250 Also note, the maintainer can simply ask for more time to review!
252 Subscribe to the ffmpeg-cvslog mailing list. The diffs of all commits
253 are sent there and reviewed by all the other developers. Bugs and possible
254 improvements or general questions regarding commits are discussed there. We
255 expect you to react if problems with your code are uncovered.
257 Update the documentation if you change behavior or add features. If you are
258 unsure how best to do this, send a patch to ffmpeg-devel, the documentation
259 maintainer(s) will review and commit your stuff.
261 Try to keep important discussions and requests (also) on the public
262 developer mailing list, so that all developers can benefit from them.
264 Never write to unallocated memory, never write over the end of arrays,
265 always check values read from some untrusted source before using them
266 as array index or other risky things.
268 Remember to check if you need to bump versions for the specific libav
269 parts (libavutil, libavcodec, libavformat) you are changing. You need
270 to change the version integer.
271 Incrementing the first component means no backward compatibility to
272 previous versions (e.g. removal of a function from the public API).
273 Incrementing the second component means backward compatible change
274 (e.g. addition of a function to the public API or extension of an
275 existing data structure).
276 Incrementing the third component means a noteworthy binary compatible
277 change (e.g. encoder bug fix that matters for the decoder).
279 Compiler warnings indicate potential bugs or code with bad style. If a type of
280 warning always points to correct and clean code, that warning should
281 be disabled, not the code changed.
282 Thus the remaining warnings can either be bugs or correct code.
283 If it is a bug, the bug has to be fixed. If it is not, the code should
284 be changed to not generate a warning unless that causes a slowdown
285 or obfuscates the code.
287 If you add a new file, give it a proper license header. Do not copy and
288 paste it from a random place, use an existing file as template.
291 We think our rules are not too hard. If you have comments, contact us.
293 Note, these rules are mostly borrowed from the MPlayer project.
295 @anchor{Submitting patches}
296 @section Submitting patches
298 First, read the @ref{Coding Rules} above if you did not yet, in particular
299 the rules regarding patch submission.
301 When you submit your patch, please use @code{git format-patch} or
302 @code{git send-email}. We cannot read other diffs :-)
304 Also please do not submit a patch which contains several unrelated changes.
305 Split it into separate, self-contained pieces. This does not mean splitting
306 file by file. Instead, make the patch as small as possible while still
307 keeping it as a logical unit that contains an individual change, even
308 if it spans multiple files. This makes reviewing your patches much easier
309 for us and greatly increases your chances of getting your patch applied.
311 Use the patcheck tool of FFmpeg to check your patch.
312 The tool is located in the tools directory.
314 Run the @ref{Regression Tests} before submitting a patch in order to verify
315 it does not cause unexpected problems.
317 Patches should be posted as base64 encoded attachments (or any other
318 encoding which ensures that the patch will not be trashed during
319 transmission) to the ffmpeg-devel mailing list, see
320 @url{http://lists.ffmpeg.org/mailman/listinfo/ffmpeg-devel}
322 It also helps quite a bit if you tell us what the patch does (for example
323 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
326 Also please if you send several patches, send each patch as a separate mail,
327 do not attach several unrelated patches to the same mail.
329 Your patch will be reviewed on the mailing list. You will likely be asked
330 to make some changes and are expected to send in an improved version that
331 incorporates the requests from the review. This process may go through
332 several iterations. Once your patch is deemed good enough, some developer
333 will pick it up and commit it to the official FFmpeg tree.
335 Give us a few days to react. But if some time passes without reaction,
336 send a reminder by email. Your patch should eventually be dealt with.
339 @section New codecs or formats checklist
343 Did you use av_cold for codec initialization and close functions?
345 Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
346 AVInputFormat/AVOutputFormat struct?
348 Did you bump the minor version number (and reset the micro version
349 number) in @file{libavcodec/version.h} or @file{libavformat/version.h}?
351 Did you register it in @file{allcodecs.c} or @file{allformats.c}?
353 Did you add the CodecID to @file{avcodec.h}?
355 If it has a fourCC, did you add it to @file{libavformat/riff.c},
356 even if it is only a decoder?
358 Did you add a rule to compile the appropriate files in the Makefile?
359 Remember to do this even if you're just adding a format to a file that is
360 already being compiled by some other rule, like a raw demuxer.
362 Did you add an entry to the table of supported formats or codecs in
363 @file{doc/general.texi}?
365 Did you add an entry in the Changelog?
367 If it depends on a parser or a library, did you add that dependency in
370 Did you @code{git add} the appropriate files before committing?
372 Did you make sure it compiles standalone, i.e. with
373 @code{configure --disable-everything --enable-decoder=foo}
374 (or @code{--enable-demuxer} or whatever your component is)?
378 @section patch submission checklist
382 Does @code{make fate} pass with the patch applied?
384 Was the patch generated with git format-patch or send-email?
386 Did you sign off your patch? (git commit -s)
387 See @url{http://kerneltrap.org/files/Jeremy/DCO.txt} for the meaning
390 Did you provide a clear git commit log message?
392 Is the patch against latest FFmpeg git master branch?
394 Are you subscribed to ffmpeg-devel?
395 (the list is subscribers only due to spam)
397 Have you checked that the changes are minimal, so that the same cannot be
398 achieved with a smaller patch and/or simpler final code?
400 If the change is to speed critical code, did you benchmark it?
402 If you did any benchmarks, did you provide them in the mail?
404 Have you checked that the patch does not introduce buffer overflows or
405 other security issues?
407 Did you test your decoder or demuxer against damaged data? If no, see
408 tools/trasher and the noise bitstream filter. Your decoder or demuxer
409 should not crash or end in a (near) infinite loop when fed damaged data.
411 Does the patch not mix functional and cosmetic changes?
413 Did you add tabs or trailing whitespace to the code? Both are forbidden.
415 Is the patch attached to the email you send?
417 Is the mime type of the patch correct? It should be text/x-diff or
418 text/x-patch or at least text/plain and not application/octet-stream.
420 If the patch fixes a bug, did you provide a verbose analysis of the bug?
422 If the patch fixes a bug, did you provide enough information, including
423 a sample, so the bug can be reproduced and the fix can be verified?
424 Note please do not attach samples >100k to mails but rather provide a
425 URL, you can upload to ftp://upload.ffmpeg.org
427 Did you provide a verbose summary about what the patch does change?
429 Did you provide a verbose explanation why it changes things like it does?
431 Did you provide a verbose summary of the user visible advantages and
432 disadvantages if the patch is applied?
434 Did you provide an example so we can verify the new feature added by the
437 If you added a new file, did you insert a license header? It should be
438 taken from FFmpeg, not randomly copied and pasted from somewhere else.
440 You should maintain alphabetical order in alphabetically ordered lists as
441 long as doing so does not break API/ABI compatibility.
443 Lines with similar content should be aligned vertically when doing so
444 improves readability.
446 Consider to add a regression test for your code.
448 If you added YASM code please check that things still work with --disable-yasm
451 @section Patch review process
453 All patches posted to ffmpeg-devel will be reviewed, unless they contain a
454 clear note that the patch is not for the git master branch.
455 Reviews and comments will be posted as replies to the patch on the
456 mailing list. The patch submitter then has to take care of every comment,
457 that can be by resubmitting a changed patch or by discussion. Resubmitted
458 patches will themselves be reviewed like any other patch. If at some point
459 a patch passes review with no comments then it is approved, that can for
460 simple and small patches happen immediately while large patches will generally
461 have to be changed and reviewed many times before they are approved.
462 After a patch is approved it will be committed to the repository.
464 We will review all submitted patches, but sometimes we are quite busy so
465 especially for large patches this can take several weeks.
467 If you feel that the review process is too slow and you are willing to try to
468 take over maintainership of the area of code you change then just clone
469 git master and maintain the area of code there. We will merge each area from
470 where its best maintained.
472 When resubmitting patches, please do not make any significant changes
473 not related to the comments received during review. Such patches will
474 be rejected. Instead, submit significant changes or new features as
477 @section Regression tests
479 Before submitting a patch (or committing to the repository), you should at least
480 test that you did not break anything.
482 Running 'make fate' accomplishes this, please see @file{doc/fate.txt} for details.
484 [Of course, some patches may change the results of the regression tests. In
485 this case, the reference results of the regression tests shall be modified