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.
40 FFmpeg is programmed in the ISO C90 language with a few additional
41 features from ISO C99, namely:
44 the @samp{inline} keyword;
48 designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
50 compound literals (@samp{x = (struct s) @{ 17, 23 @};})
53 These features are supported by all compilers we care about, so we will not
54 accept patches to remove their use unless they absolutely do not impair
55 clarity and performance.
57 All code must compile with GCC 2.95 and GCC 3.3. Currently, FFmpeg also
58 compiles with several other compilers, such as the Compaq ccc compiler
59 or Sun Studio 9, and we would like to keep it that way unless it would
60 be exceedingly involved. To ensure compatibility, please do not use any
61 additional C99 features or GCC extensions. Especially watch out for:
64 mixing statements and declarations;
66 @samp{long long} (use @samp{int64_t} instead);
68 @samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;
70 GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
74 The presentation is one inspired by 'indent -i4 -kr -nut'.
75 The TAB character is forbidden outside of Makefiles as is any
76 form of trailing whitespace. Commits containing either will be
77 rejected by the git repository.
79 The main priority in FFmpeg is simplicity and small code size in order to
80 minimize the bug count.
82 Comments: Use the JavaDoc/Doxygen
83 format (see examples below) so that code documentation
84 can be generated automatically. All nontrivial functions should have a comment
85 above them explaining what the function does, even if it is just one sentence.
86 All structures and their member variables should be documented, too.
99 typedef struct Foobar@{
100 int var1; /**< var1 description */
101 int var2; ///< var2 description
102 /** var3 description */
110 * @@param my_parameter description of my_parameter
111 * @@return return value description
113 int myfunc(int my_parameter)
117 fprintf and printf are forbidden in libavformat and libavcodec,
118 please use av_log() instead.
120 Casts should be used only when necessary. Unneeded parentheses
121 should also be avoided if they don't make the code easier to understand.
123 @section Development Policy
127 Contributions should be licensed under the LGPL 2.1, including an
128 "or any later version" clause, or the MIT license. GPL 2 including
129 an "or any later version" clause is also acceptable, but LGPL is
132 You must not commit code which breaks FFmpeg! (Meaning unfinished but
133 enabled code which breaks compilation or compiles but does not work or
134 breaks the regression tests)
135 You can commit unfinished stuff (for testing etc), but it must be disabled
136 (#ifdef etc) by default so it does not interfere with other developers'
139 You do not have to over-test things. If it works for you, and you think it
140 should work for others, then commit. If your code has problems
141 (portability, triggers compiler bugs, unusual environment etc) they will be
142 reported and eventually fixed.
144 Do not commit unrelated changes together, split them into self-contained
145 pieces. Also do not forget that if part B depends on part A, but A does not
146 depend on B, then A can and should be committed first and separate from B.
147 Keeping changes well split into self-contained parts makes reviewing and
148 understanding them on the commit log mailing list easier. This also helps
149 in case of debugging later on.
150 Also if you have doubts about splitting or not splitting, do not hesitate to
151 ask/discuss it on the developer mailing list.
153 Do not change behavior of the programs (renaming options etc) or public
154 API or ABI without first discussing it on the ffmpeg-devel mailing list.
155 Do not remove functionality from the code. Just improve!
157 Note: Redundant code can be removed.
159 Do not commit changes to the build system (Makefiles, configure script)
160 which change behavior, defaults etc, without asking first. The same
161 applies to compiler warning fixes, trivial looking fixes and to code
162 maintained by other developers. We usually have a reason for doing things
163 the way we do. Send your changes as patches to the ffmpeg-devel mailing
164 list, and if the code maintainers say OK, you may commit. This does not
165 apply to files you wrote and/or maintain.
167 We refuse source indentation and other cosmetic changes if they are mixed
168 with functional changes, such commits will be rejected and removed. Every
169 developer has his own indentation style, you should not change it. Of course
170 if you (re)write something, you can use your own style, even though we would
171 prefer if the indentation throughout FFmpeg was consistent (Many projects
172 force a given indentation style - we do not.). If you really need to make
173 indentation changes (try to avoid this), separate them strictly from real
176 NOTE: If you had to put if()@{ .. @} over a large (> 5 lines) chunk of code,
177 then either do NOT change the indentation of the inner part within (do not
178 move it to the right)! or do so in a separate commit
180 Always fill out the commit log message. Describe in a few lines what you
181 changed and why. You can refer to mailing list postings if you fix a
182 particular bug. Comments such as "fixed!" or "Changed it." are unacceptable.
184 If you apply a patch by someone else, include the name and email address in
185 the log message. Since the ffmpeg-cvslog mailing list is publicly
186 archived you should add some SPAM protection to the email address. Send an
187 answer to ffmpeg-devel (or wherever you got the patch from) saying that
188 you applied the patch.
190 When applying patches that have been discussed (at length) on the mailing
191 list, reference the thread in the log message.
193 Do NOT commit to code actively maintained by others without permission.
194 Send a patch to ffmpeg-devel instead. If no one answers within a reasonable
195 timeframe (12h for build failures and security fixes, 3 days small changes,
196 1 week for big patches) then commit your patch if you think it is OK.
197 Also note, the maintainer can simply ask for more time to review!
199 Subscribe to the ffmpeg-cvslog mailing list. The diffs of all commits
200 are sent there and reviewed by all the other developers. Bugs and possible
201 improvements or general questions regarding commits are discussed there. We
202 expect you to react if problems with your code are uncovered.
204 Update the documentation if you change behavior or add features. If you are
205 unsure how best to do this, send a patch to ffmpeg-devel, the documentation
206 maintainer(s) will review and commit your stuff.
208 Try to keep important discussions and requests (also) on the public
209 developer mailing list, so that all developers can benefit from them.
211 Never write to unallocated memory, never write over the end of arrays,
212 always check values read from some untrusted source before using them
213 as array index or other risky things.
215 Remember to check if you need to bump versions for the specific libav
216 parts (libavutil, libavcodec, libavformat) you are changing. You need
217 to change the version integer.
218 Incrementing the first component means no backward compatibility to
219 previous versions (e.g. removal of a function from the public API).
220 Incrementing the second component means backward compatible change
221 (e.g. addition of a function to the public API or extension of an
222 existing data structure).
223 Incrementing the third component means a noteworthy binary compatible
224 change (e.g. encoder bug fix that matters for the decoder).
226 Compiler warnings indicate potential bugs or code with bad style. If a type of
227 warning always points to correct and clean code, that warning should
228 be disabled, not the code changed.
229 Thus the remaining warnings can either be bugs or correct code.
230 If it is a bug, the bug has to be fixed. If it is not, the code should
231 be changed to not generate a warning unless that causes a slowdown
232 or obfuscates the code.
234 If you add a new file, give it a proper license header. Do not copy and
235 paste it from a random place, use an existing file as template.
238 We think our rules are not too hard. If you have comments, contact us.
240 Note, these rules are mostly borrowed from the MPlayer project.
242 @section Submitting patches
244 First, (@pxref{Coding Rules}) above if you did not yet.
246 When you submit your patch, try to send a unified diff (diff '-up'
247 option). We cannot read other diffs :-)
249 Also please do not submit a patch which contains several unrelated changes.
250 Split it into separate, self-contained pieces. This does not mean splitting
251 file by file. Instead, make the patch as small as possible while still
252 keeping it as a logical unit that contains an individual change, even
253 if it spans multiple files. This makes reviewing your patches much easier
254 for us and greatly increases your chances of getting your patch applied.
256 Use the patcheck tool of FFmpeg to check your patch.
257 The tool is located in the tools directory.
259 Run the regression tests before submitting a patch so that you can
260 verify that there are no big problems.
262 Patches should be posted as base64 encoded attachments (or any other
263 encoding which ensures that the patch will not be trashed during
264 transmission) to the ffmpeg-devel mailing list, see
265 @url{http://lists.ffmpeg.org/mailman/listinfo/ffmpeg-devel}
267 It also helps quite a bit if you tell us what the patch does (for example
268 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
271 Also please if you send several patches, send each patch as a separate mail,
272 do not attach several unrelated patches to the same mail.
274 Your patch will be reviewed on the mailing list. You will likely be asked
275 to make some changes and are expected to send in an improved version that
276 incorporates the requests from the review. This process may go through
277 several iterations. Once your patch is deemed good enough, some developer
278 will pick it up and commit it to the official FFmpeg tree.
280 Give us a few days to react. But if some time passes without reaction,
281 send a reminder by email. Your patch should eventually be dealt with.
284 @section New codecs or formats checklist
288 Did you use av_cold for codec initialization and close functions?
290 Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
291 AVInputFormat/AVOutputFormat struct?
293 Did you bump the minor version number (and reset the micro version
294 number) in @file{avcodec.h} or @file{avformat.h}?
296 Did you register it in @file{allcodecs.c} or @file{allformats.c}?
298 Did you add the CodecID to @file{avcodec.h}?
300 If it has a fourcc, did you add it to @file{libavformat/riff.c},
301 even if it is only a decoder?
303 Did you add a rule to compile the appropriate files in the Makefile?
304 Remember to do this even if you're just adding a format to a file that is
305 already being compiled by some other rule, like a raw demuxer.
307 Did you add an entry to the table of supported formats or codecs in
308 @file{doc/general.texi}?
310 Did you add an entry in the Changelog?
312 If it depends on a parser or a library, did you add that dependency in
315 Did you "git add" the appropriate files before committing?
318 @section patch submission checklist
322 Does 'make fate' pass with the patch applied?
324 Was the patch generated with git format-patch or send-email?
326 Did you sign off your patch? (git commit -s)
327 See @url{http://kerneltrap.org/files/Jeremy/DCO.txt} for the meaning
330 Did you provide a clear git commit log message?
332 Is the patch against latest FFmpeg git master branch?
334 Are you subscribed to ffmpeg-dev?
335 (the list is subscribers only due to spam)
337 Have you checked that the changes are minimal, so that the same cannot be
338 achieved with a smaller patch and/or simpler final code?
340 If the change is to speed critical code, did you benchmark it?
342 If you did any benchmarks, did you provide them in the mail?
344 Have you checked that the patch does not introduce buffer overflows or
345 other security issues?
347 Did you test your decoder or demuxer against damaged data? If no, see
348 tools/trasher and the noise bitstream filter. Your decoder or demuxer
349 should not crash or end in a (near) infinite loop when fed damaged data.
351 Does the patch not mix functional and cosmetic changes?
353 Did you add tabs or trailing whitespace to the code? Both are forbidden.
355 Is the patch attached to the email you send?
357 Is the mime type of the patch correct? It should be text/x-diff or
358 text/x-patch or at least text/plain and not application/octet-stream.
360 If the patch fixes a bug, did you provide a verbose analysis of the bug?
362 If the patch fixes a bug, did you provide enough information, including
363 a sample, so the bug can be reproduced and the fix can be verified?
364 Note please do not attach samples >100k to mails but rather provide a
365 URL, you can upload to ftp://upload.ffmpeg.org
367 Did you provide a verbose summary about what the patch does change?
369 Did you provide a verbose explanation why it changes things like it does?
371 Did you provide a verbose summary of the user visible advantages and
372 disadvantages if the patch is applied?
374 Did you provide an example so we can verify the new feature added by the
377 If you added a new file, did you insert a license header? It should be
378 taken from FFmpeg, not randomly copied and pasted from somewhere else.
380 You should maintain alphabetical order in alphabetically ordered lists as
381 long as doing so does not break API/ABI compatibility.
383 Lines with similar content should be aligned vertically when doing so
384 improves readability.
387 @section Patch review process
389 All patches posted to ffmpeg-devel will be reviewed, unless they contain a
390 clear note that the patch is not for the git master branch.
391 Reviews and comments will be posted as replies to the patch on the
392 mailing list. The patch submitter then has to take care of every comment,
393 that can be by resubmitting a changed patch or by discussion. Resubmitted
394 patches will themselves be reviewed like any other patch. If at some point
395 a patch passes review with no comments then it is approved, that can for
396 simple and small patches happen immediately while large patches will generally
397 have to be changed and reviewed many times before they are approved.
398 After a patch is approved it will be committed to the repository.
400 We will review all submitted patches, but sometimes we are quite busy so
401 especially for large patches this can take several weeks.
403 When resubmitting patches, please do not make any significant changes
404 not related to the comments received during review. Such patches will
405 be rejected. Instead, submit significant changes or new features as
408 @section Regression tests
410 Before submitting a patch (or committing to the repository), you should at least
411 test that you did not break anything.
413 The regression tests build a synthetic video stream and a synthetic
414 audio stream. These are then encoded and decoded with all codecs or
415 formats. The CRC (or MD5) of each generated file is recorded in a
416 result file. A 'diff' is launched to compare the reference results and
417 the result file. The output is checked immediately after each test
420 The regression tests then go on to test the FFserver code with a
421 limited set of streams. It is important that this step runs correctly
424 Run 'make test' to test all the codecs and formats. Commands like
425 'make regtest-mpeg2' can be used to run a single test. By default,
426 make will abort if any test fails. To run all tests regardless,
427 use make -k. To get a more verbose output, use 'make V=1 test' or
430 Run 'make fulltest' to test all the codecs, formats and FFserver.
432 [Of course, some patches may change the results of the regression tests. In
433 this case, the reference results of the regression tests shall be modified