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.
92 typedef struct Foobar@{
93 int var1; /**< var1 description */
94 int var2; ///< var2 description
95 /** var3 description */
103 * @@param my_parameter description of my_parameter
104 * @@return return value description
106 int myfunc(int my_parameter)
110 @subsection C language features
112 FFmpeg is programmed in the ISO C90 language with a few additional
113 features from ISO C99, namely:
116 the @samp{inline} keyword;
120 designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
122 compound literals (@samp{x = (struct s) @{ 17, 23 @};})
125 These features are supported by all compilers we care about, so we will not
126 accept patches to remove their use unless they absolutely do not impair
127 clarity and performance.
129 All code must compile with recent versions of GCC and a number of other
130 currently supported compilers. To ensure compatibility, please do not use
131 additional C99 features or GCC extensions. Especially watch out for:
134 mixing statements and declarations;
136 @samp{long long} (use @samp{int64_t} instead);
138 @samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;
140 GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
143 @subsection Naming conventions
144 All names are using underscores (_), not CamelCase. For example, @samp{avfilter_get_video_buffer} is
145 a valid function name and @samp{AVFilterGetVideo} is not. The exception from this are type names, like
146 for example structs and enums; they should always be in the CamelCase
149 There are following conventions for naming variables and functions:
152 For local variables no prefix is required.
154 For variables and functions declared as @code{static} no prefixes are required.
156 For variables and functions used internally by the library, @code{ff_} prefix
158 For example, @samp{ff_w64_demuxer}.
160 For variables and functions used internally across multiple libraries, use
161 @code{avpriv_}. For example, @samp{avpriv_aac_parse_header}.
163 For exported names, each library has its own prefixes. Just check the existing
164 code and name accordingly.
167 @subsection Miscellanous conventions
170 fprintf and printf are forbidden in libavformat and libavcodec,
171 please use av_log() instead.
173 Casts should be used only when necessary. Unneeded parentheses
174 should also be avoided if they don't make the code easier to understand.
177 @section Development Policy
181 Contributions should be licensed under the LGPL 2.1, including an
182 "or any later version" clause, or the MIT license. GPL 2 including
183 an "or any later version" clause is also acceptable, but LGPL is
186 You must not commit code which breaks FFmpeg! (Meaning unfinished but
187 enabled code which breaks compilation or compiles but does not work or
188 breaks the regression tests)
189 You can commit unfinished stuff (for testing etc), but it must be disabled
190 (#ifdef etc) by default so it does not interfere with other developers'
193 You do not have to over-test things. If it works for you, and you think it
194 should work for others, then commit. If your code has problems
195 (portability, triggers compiler bugs, unusual environment etc) they will be
196 reported and eventually fixed.
198 Do not commit unrelated changes together, split them into self-contained
199 pieces. Also do not forget that if part B depends on part A, but A does not
200 depend on B, then A can and should be committed first and separate from B.
201 Keeping changes well split into self-contained parts makes reviewing and
202 understanding them on the commit log mailing list easier. This also helps
203 in case of debugging later on.
204 Also if you have doubts about splitting or not splitting, do not hesitate to
205 ask/discuss it on the developer mailing list.
207 Do not change behavior of the programs (renaming options etc) or public
208 API or ABI without first discussing it on the ffmpeg-devel mailing list.
209 Do not remove functionality from the code. Just improve!
211 Note: Redundant code can be removed.
213 Do not commit changes to the build system (Makefiles, configure script)
214 which change behavior, defaults etc, without asking first. The same
215 applies to compiler warning fixes, trivial looking fixes and to code
216 maintained by other developers. We usually have a reason for doing things
217 the way we do. Send your changes as patches to the ffmpeg-devel mailing
218 list, and if the code maintainers say OK, you may commit. This does not
219 apply to files you wrote and/or maintain.
221 We refuse source indentation and other cosmetic changes if they are mixed
222 with functional changes, such commits will be rejected and removed. Every
223 developer has his own indentation style, you should not change it. Of course
224 if you (re)write something, you can use your own style, even though we would
225 prefer if the indentation throughout FFmpeg was consistent (Many projects
226 force a given indentation style - we do not.). If you really need to make
227 indentation changes (try to avoid this), separate them strictly from real
230 NOTE: If you had to put if()@{ .. @} over a large (> 5 lines) chunk of code,
231 then either do NOT change the indentation of the inner part within (do not
232 move it to the right)! or do so in a separate commit
234 Always fill out the commit log message. Describe in a few lines what you
235 changed and why. You can refer to mailing list postings if you fix a
236 particular bug. Comments such as "fixed!" or "Changed it." are unacceptable.
238 area changed: Short 1 line description
240 details describing what and why and giving references.
242 Make sure the author of the commit is set correctly. (see git commit --author)
243 If you apply a patch, send an
244 answer to ffmpeg-devel (or wherever you got the patch from) saying that
245 you applied the patch.
247 When applying patches that have been discussed (at length) on the mailing
248 list, reference the thread in the log message.
250 Do NOT commit to code actively maintained by others without permission.
251 Send a patch to ffmpeg-devel instead. If no one answers within a reasonable
252 timeframe (12h for build failures and security fixes, 3 days small changes,
253 1 week for big patches) then commit your patch if you think it is OK.
254 Also note, the maintainer can simply ask for more time to review!
256 Subscribe to the ffmpeg-cvslog mailing list. The diffs of all commits
257 are sent there and reviewed by all the other developers. Bugs and possible
258 improvements or general questions regarding commits are discussed there. We
259 expect you to react if problems with 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 a patch to ffmpeg-devel, the documentation
263 maintainer(s) will review and commit your stuff.
265 Try to keep important discussions and requests (also) on the public
266 developer mailing list, so that all developers can benefit from them.
268 Never write to unallocated memory, never write over the end of arrays,
269 always check values read from some untrusted source before using them
270 as array index or other risky things.
272 Remember to check if you need to bump versions for the specific libav
273 parts (libavutil, libavcodec, libavformat) you are changing. You need
274 to change the version integer.
275 Incrementing the first component means no backward compatibility to
276 previous versions (e.g. removal of a function from the public API).
277 Incrementing the second component means backward compatible change
278 (e.g. addition of a function to the public API or extension of an
279 existing data structure).
280 Incrementing the third component means a noteworthy binary compatible
281 change (e.g. encoder bug fix that matters for the decoder).
283 Compiler warnings indicate potential bugs or code with bad style. If a type of
284 warning always points to correct and clean code, that warning should
285 be disabled, not the code changed.
286 Thus the remaining warnings can either be bugs or correct code.
287 If it is a bug, the bug has to be fixed. If it is not, the code should
288 be changed to not generate a warning unless that causes a slowdown
289 or obfuscates the code.
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, these rules are mostly borrowed from the MPlayer project.
299 @anchor{Submitting patches}
300 @section Submitting patches
302 First, read the @ref{Coding Rules} above if you did not yet, in particular
303 the rules regarding patch submission.
305 When you submit your patch, please use @code{git format-patch} or
306 @code{git send-email}. We cannot read other diffs :-)
308 Also please do not submit a patch which contains several unrelated changes.
309 Split it into separate, self-contained pieces. This does not mean splitting
310 file by file. Instead, make the patch as small as possible while still
311 keeping it as a logical unit that contains an individual change, even
312 if it spans multiple files. This makes reviewing your patches much easier
313 for us and greatly increases your chances of getting your patch applied.
315 Use the patcheck tool of FFmpeg to check your patch.
316 The tool is located in the tools directory.
318 Run the @ref{Regression Tests} before submitting a patch in order to verify
319 it does not cause unexpected problems.
321 Patches should be posted as base64 encoded attachments (or any other
322 encoding which ensures that the patch will not be trashed during
323 transmission) to the ffmpeg-devel mailing list, see
324 @url{http://lists.ffmpeg.org/mailman/listinfo/ffmpeg-devel}
326 It also helps quite a bit if you tell us what the patch does (for example
327 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
330 Also please if you send several patches, send each patch as a separate mail,
331 do not attach several unrelated patches to the same mail.
333 Your patch will be reviewed on the mailing list. You will likely be asked
334 to make some changes and are expected to send in an improved version that
335 incorporates the requests from the review. This process may go through
336 several iterations. Once your patch is deemed good enough, some developer
337 will pick it up and commit it to the official FFmpeg tree.
339 Give us a few days to react. But if some time passes without reaction,
340 send a reminder by email. Your patch should eventually be dealt with.
343 @section New codecs or formats checklist
347 Did you use av_cold for codec initialization and close functions?
349 Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
350 AVInputFormat/AVOutputFormat struct?
352 Did you bump the minor version number (and reset the micro version
353 number) in @file{libavcodec/version.h} or @file{libavformat/version.h}?
355 Did you register it in @file{allcodecs.c} or @file{allformats.c}?
357 Did you add the CodecID to @file{avcodec.h}?
359 If it has a fourCC, did you add it to @file{libavformat/riff.c},
360 even if it is only a decoder?
362 Did you add a rule to compile the appropriate files in the Makefile?
363 Remember to do this even if you're just adding a format to a file that is
364 already being compiled by some other rule, like a raw demuxer.
366 Did you add an entry to the table of supported formats or codecs in
367 @file{doc/general.texi}?
369 Did you add an entry in the Changelog?
371 If it depends on a parser or a library, did you add that dependency in
374 Did you @code{git add} the appropriate files before committing?
376 Did you make sure it compiles standalone, i.e. with
377 @code{configure --disable-everything --enable-decoder=foo}
378 (or @code{--enable-demuxer} or whatever your component is)?
382 @section patch submission checklist
386 Does @code{make fate} pass with the patch applied?
388 Was the patch generated with git format-patch or send-email?
390 Did you sign off your patch? (git commit -s)
391 See @url{http://kerneltrap.org/files/Jeremy/DCO.txt} for the meaning
394 Did you provide a clear git commit log message?
396 Is the patch against latest FFmpeg git master branch?
398 Are you subscribed to ffmpeg-devel?
399 (the list is subscribers only due to spam)
401 Have you checked that the changes are minimal, so that the same cannot be
402 achieved with a smaller patch and/or simpler final code?
404 If the change is to speed critical code, did you benchmark it?
406 If you did any benchmarks, did you provide them in the mail?
408 Have you checked that the patch does not introduce buffer overflows or
409 other security issues?
411 Did you test your decoder or demuxer against damaged data? If no, see
412 tools/trasher and the noise bitstream filter. Your decoder or demuxer
413 should not crash or end in a (near) infinite loop when fed damaged data.
415 Does the patch not mix functional and cosmetic changes?
417 Did you add tabs or trailing whitespace to the code? Both are forbidden.
419 Is the patch attached to the email you send?
421 Is the mime type of the patch correct? It should be text/x-diff or
422 text/x-patch or at least text/plain and not application/octet-stream.
424 If the patch fixes a bug, did you provide a verbose analysis of the bug?
426 If the patch fixes a bug, did you provide enough information, including
427 a sample, so the bug can be reproduced and the fix can be verified?
428 Note please do not attach samples >100k to mails but rather provide a
429 URL, you can upload to ftp://upload.ffmpeg.org
431 Did you provide a verbose summary about what the patch does change?
433 Did you provide a verbose explanation why it changes things like it does?
435 Did you provide a verbose summary of the user visible advantages and
436 disadvantages if the patch is applied?
438 Did you provide an example so we can verify the new feature added by the
441 If you added a new file, did you insert a license header? It should be
442 taken from FFmpeg, not randomly copied and pasted from somewhere else.
444 You should maintain alphabetical order in alphabetically ordered lists as
445 long as doing so does not break API/ABI compatibility.
447 Lines with similar content should be aligned vertically when doing so
448 improves readability.
450 Consider to add a regression test for your code.
452 If you added YASM code please check that things still work with --disable-yasm
455 @section Patch review process
457 All patches posted to ffmpeg-devel 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 If you feel that the review process is too slow and you are willing to try to
472 take over maintainership of the area of code you change then just clone
473 git master and maintain the area of code there. We will merge each area from
474 where its best maintained.
476 When resubmitting patches, please do not make any significant changes
477 not related to the comments received during review. Such patches will
478 be rejected. Instead, submit significant changes or new features as
481 @section Regression tests
483 Before submitting a patch (or committing to the repository), you should at least
484 test that you did not break anything.
486 Running 'make fate' accomplishes this, please see @file{doc/fate.txt} for details.
488 [Of course, some patches may change the results of the regression tests. In
489 this case, the reference results of the regression tests shall be modified