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45 <h1 class="settitle">Developer Documentation</h1>
47 <a name="SEC_Contents"></a>
48 <h1>Table of Contents</h1>
49 <div class="contents">
52 <li><a name="toc-Developers-Guide" href="#Developers-Guide">1. Developers Guide</a>
54 <li><a name="toc-API" href="#API">1.1 API</a></li>
55 <li><a name="toc-Integrating-libavcodec-or-libavformat-in-your-program" href="#Integrating-libavcodec-or-libavformat-in-your-program">1.2 Integrating libavcodec or libavformat in your program</a></li>
56 <li><a name="toc-Contributing" href="#Contributing">1.3 Contributing</a></li>
57 <li><a name="toc-Coding-Rules-1" href="#Coding-Rules-1">1.4 Coding Rules</a></li>
58 <li><a name="toc-Development-Policy" href="#Development-Policy">1.5 Development Policy</a></li>
59 <li><a name="toc-Submitting-patches-1" href="#Submitting-patches-1">1.6 Submitting patches</a></li>
60 <li><a name="toc-New-codecs-or-formats-checklist" href="#New-codecs-or-formats-checklist">1.7 New codecs or formats checklist</a></li>
61 <li><a name="toc-patch-submission-checklist" href="#patch-submission-checklist">1.8 patch submission checklist</a></li>
62 <li><a name="toc-Patch-review-process" href="#Patch-review-process">1.9 Patch review process</a></li>
63 <li><a name="toc-Regression-tests" href="#Regression-tests">1.10 Regression tests</a></li>
70 <a name="Developers-Guide"></a>
71 <h1 class="chapter"><a href="developer.html#toc-Developers-Guide">1. Developers Guide</a></h1>
74 <h2 class="section"><a href="developer.html#toc-API">1.1 API</a></h2>
76 <li> libavcodec is the library containing the codecs (both encoding and
77 decoding). Look at ‘<tt>libavcodec/apiexample.c</tt>’ to see how to use it.
79 </li><li> libavformat is the library containing the file format handling (mux and
80 demux code for several formats). Look at ‘<tt>ffplay.c</tt>’ to use it in a
81 player. See ‘<tt>libavformat/output-example.c</tt>’ to use it to generate
82 audio or video streams.
86 <a name="Integrating-libavcodec-or-libavformat-in-your-program"></a>
87 <h2 class="section"><a href="developer.html#toc-Integrating-libavcodec-or-libavformat-in-your-program">1.2 Integrating libavcodec or libavformat in your program</a></h2>
89 <p>You can integrate all the source code of the libraries to link them
90 statically to avoid any version problem. All you need is to provide a
91 ’config.mak’ and a ’config.h’ in the parent directory. See the defines
92 generated by ./configure to understand what is needed.
94 <p>You can use libavcodec or libavformat in your commercial program, but
95 <em>any patch you make must be published</em>. The best way to proceed is
96 to send your patches to the FFmpeg mailing list.
98 <a name="Contributing"></a>
99 <h2 class="section"><a href="developer.html#toc-Contributing">1.3 Contributing</a></h2>
101 <p>There are 3 ways by which code gets into ffmpeg.
103 <li> Submiting Patches to the main developer mailing list
104 see <a href="#Submitting-patches">Submitting patches</a> for details.
105 </li><li> Directly commiting changes to the main tree.
106 </li><li> Commiting changes to a git clone, for example on github.com or
107 gitorious.org. And asking us to merge these changes.
110 <p>Whichever way, changes should be reviewed by the maintainer of the code
111 before they are commited. And they should follow the <a href="#Coding-Rules">Coding Rules</a>.
112 The developer making the commit and the author are responsible for their changes
113 and should try to fix issues their commit causes.
115 <p><a name="Coding-Rules"></a>
116 </p><a name="Coding-Rules-1"></a>
117 <h2 class="section"><a href="developer.html#toc-Coding-Rules-1">1.4 Coding Rules</a></h2>
119 <p>FFmpeg is programmed in the ISO C90 language with a few additional
120 features from ISO C99, namely:
123 the ‘<samp>inline</samp>’ keyword;
125 ‘<samp>//</samp>’ comments;
127 designated struct initializers (‘<samp>struct s x = { .i = 17 };</samp>’)
129 compound literals (‘<samp>x = (struct s) { 17, 23 };</samp>’)
132 <p>These features are supported by all compilers we care about, so we will not
133 accept patches to remove their use unless they absolutely do not impair
134 clarity and performance.
136 <p>All code must compile with recent versions of GCC and a number of other
137 currently supported compilers. To ensure compatibility, please do not use
138 additional C99 features or GCC extensions. Especially watch out for:
141 mixing statements and declarations;
143 ‘<samp>long long</samp>’ (use ‘<samp>int64_t</samp>’ instead);
145 ‘<samp>__attribute__</samp>’ not protected by ‘<samp>#ifdef __GNUC__</samp>’ or similar;
147 GCC statement expressions (‘<samp>(x = ({ int y = 4; y; })</samp>’).
151 The presentation is one inspired by ’indent -i4 -kr -nut’.
152 The TAB character is forbidden outside of Makefiles as is any
153 form of trailing whitespace. Commits containing either will be
154 rejected by the git repository.
156 <p>The main priority in FFmpeg is simplicity and small code size in order to
157 minimize the bug count.
159 <p>Comments: Use the JavaDoc/Doxygen
160 format (see examples below) so that code documentation
161 can be generated automatically. All nontrivial functions should have a comment
162 above them explaining what the function does, even if it is just one sentence.
163 All structures and their member variables should be documented, too.
164 </p><table><tr><td> </td><td><pre class="example">/**
175 typedef struct Foobar{
176 int var1; /**< var1 description */
177 int var2; ///< var2 description
178 /** var3 description */
186 * @param my_parameter description of my_parameter
187 * @return return value description
189 int myfunc(int my_parameter)
191 </pre></td></tr></table>
193 <p>fprintf and printf are forbidden in libavformat and libavcodec,
194 please use av_log() instead.
196 <p>Casts should be used only when necessary. Unneeded parentheses
197 should also be avoided if they don’t make the code easier to understand.
199 <a name="Development-Policy"></a>
200 <h2 class="section"><a href="developer.html#toc-Development-Policy">1.5 Development Policy</a></h2>
204 Contributions should be licensed under the LGPL 2.1, including an
205 "or any later version" clause, or the MIT license. GPL 2 including
206 an "or any later version" clause is also acceptable, but LGPL is
209 You must not commit code which breaks FFmpeg! (Meaning unfinished but
210 enabled code which breaks compilation or compiles but does not work or
211 breaks the regression tests)
212 You can commit unfinished stuff (for testing etc), but it must be disabled
213 (#ifdef etc) by default so it does not interfere with other developers’
216 You do not have to over-test things. If it works for you, and you think it
217 should work for others, then commit. If your code has problems
218 (portability, triggers compiler bugs, unusual environment etc) they will be
219 reported and eventually fixed.
221 Do not commit unrelated changes together, split them into self-contained
222 pieces. Also do not forget that if part B depends on part A, but A does not
223 depend on B, then A can and should be committed first and separate from B.
224 Keeping changes well split into self-contained parts makes reviewing and
225 understanding them on the commit log mailing list easier. This also helps
226 in case of debugging later on.
227 Also if you have doubts about splitting or not splitting, do not hesitate to
228 ask/discuss it on the developer mailing list.
230 Do not change behavior of the programs (renaming options etc) or public
231 API or ABI without first discussing it on the ffmpeg-devel mailing list.
232 Do not remove functionality from the code. Just improve!
234 <p> Note: Redundant code can be removed.
236 Do not commit changes to the build system (Makefiles, configure script)
237 which change behavior, defaults etc, without asking first. The same
238 applies to compiler warning fixes, trivial looking fixes and to code
239 maintained by other developers. We usually have a reason for doing things
240 the way we do. Send your changes as patches to the ffmpeg-devel mailing
241 list, and if the code maintainers say OK, you may commit. This does not
242 apply to files you wrote and/or maintain.
244 We refuse source indentation and other cosmetic changes if they are mixed
245 with functional changes, such commits will be rejected and removed. Every
246 developer has his own indentation style, you should not change it. Of course
247 if you (re)write something, you can use your own style, even though we would
248 prefer if the indentation throughout FFmpeg was consistent (Many projects
249 force a given indentation style - we do not.). If you really need to make
250 indentation changes (try to avoid this), separate them strictly from real
253 <p> NOTE: If you had to put if(){ .. } over a large (> 5 lines) chunk of code,
254 then either do NOT change the indentation of the inner part within (do not
255 move it to the right)! or do so in a separate commit
257 Always fill out the commit log message. Describe in a few lines what you
258 changed and why. You can refer to mailing list postings if you fix a
259 particular bug. Comments such as "fixed!" or "Changed it." are unacceptable.
261 area changed: Short 1 line description
263 <p> details describing what and why and giving references.
265 Make sure the author of the commit is set correctly. (see git commit –author)
266 If you apply a patch, send an
267 answer to ffmpeg-devel (or wherever you got the patch from) saying that
268 you applied the patch.
270 When applying patches that have been discussed (at length) on the mailing
271 list, reference the thread in the log message.
273 Do NOT commit to code actively maintained by others without permission.
274 Send a patch to ffmpeg-devel instead. If no one answers within a reasonable
275 timeframe (12h for build failures and security fixes, 3 days small changes,
276 1 week for big patches) then commit your patch if you think it is OK.
277 Also note, the maintainer can simply ask for more time to review!
279 Subscribe to the ffmpeg-cvslog mailing list. The diffs of all commits
280 are sent there and reviewed by all the other developers. Bugs and possible
281 improvements or general questions regarding commits are discussed there. We
282 expect you to react if problems with your code are uncovered.
284 Update the documentation if you change behavior or add features. If you are
285 unsure how best to do this, send a patch to ffmpeg-devel, the documentation
286 maintainer(s) will review and commit your stuff.
288 Try to keep important discussions and requests (also) on the public
289 developer mailing list, so that all developers can benefit from them.
291 Never write to unallocated memory, never write over the end of arrays,
292 always check values read from some untrusted source before using them
293 as array index or other risky things.
295 Remember to check if you need to bump versions for the specific libav
296 parts (libavutil, libavcodec, libavformat) you are changing. You need
297 to change the version integer.
298 Incrementing the first component means no backward compatibility to
299 previous versions (e.g. removal of a function from the public API).
300 Incrementing the second component means backward compatible change
301 (e.g. addition of a function to the public API or extension of an
302 existing data structure).
303 Incrementing the third component means a noteworthy binary compatible
304 change (e.g. encoder bug fix that matters for the decoder).
306 Compiler warnings indicate potential bugs or code with bad style. If a type of
307 warning always points to correct and clean code, that warning should
308 be disabled, not the code changed.
309 Thus the remaining warnings can either be bugs or correct code.
310 If it is a bug, the bug has to be fixed. If it is not, the code should
311 be changed to not generate a warning unless that causes a slowdown
312 or obfuscates the code.
314 If you add a new file, give it a proper license header. Do not copy and
315 paste it from a random place, use an existing file as template.
318 <p>We think our rules are not too hard. If you have comments, contact us.
320 <p>Note, these rules are mostly borrowed from the MPlayer project.
322 <p><a name="Submitting-patches"></a>
323 </p><a name="Submitting-patches-1"></a>
324 <h2 class="section"><a href="developer.html#toc-Submitting-patches-1">1.6 Submitting patches</a></h2>
326 <p>First, read the <a href="#Coding-Rules">Coding Rules</a> above if you did not yet, in particular
327 the rules regarding patch submission.
329 <p>When you submit your patch, please use <code>git format-patch</code> or
330 <code>git send-email</code>. We cannot read other diffs :-)
332 <p>Also please do not submit a patch which contains several unrelated changes.
333 Split it into separate, self-contained pieces. This does not mean splitting
334 file by file. Instead, make the patch as small as possible while still
335 keeping it as a logical unit that contains an individual change, even
336 if it spans multiple files. This makes reviewing your patches much easier
337 for us and greatly increases your chances of getting your patch applied.
339 <p>Use the patcheck tool of FFmpeg to check your patch.
340 The tool is located in the tools directory.
342 <p>Run the @ref{Regression Tests} before submitting a patch in order to verify
343 it does not cause unexpected problems.
345 <p>Patches should be posted as base64 encoded attachments (or any other
346 encoding which ensures that the patch will not be trashed during
347 transmission) to the ffmpeg-devel mailing list, see
348 <a href="http://lists.ffmpeg.org/mailman/listinfo/ffmpeg-devel">http://lists.ffmpeg.org/mailman/listinfo/ffmpeg-devel</a>
350 <p>It also helps quite a bit if you tell us what the patch does (for example
351 ’replaces lrint by lrintf’), and why (for example ’*BSD isn’t C99 compliant
352 and has no lrint()’)
354 <p>Also please if you send several patches, send each patch as a separate mail,
355 do not attach several unrelated patches to the same mail.
357 <p>Your patch will be reviewed on the mailing list. You will likely be asked
358 to make some changes and are expected to send in an improved version that
359 incorporates the requests from the review. This process may go through
360 several iterations. Once your patch is deemed good enough, some developer
361 will pick it up and commit it to the official FFmpeg tree.
363 <p>Give us a few days to react. But if some time passes without reaction,
364 send a reminder by email. Your patch should eventually be dealt with.
367 <a name="New-codecs-or-formats-checklist"></a>
368 <h2 class="section"><a href="developer.html#toc-New-codecs-or-formats-checklist">1.7 New codecs or formats checklist</a></h2>
372 Did you use av_cold for codec initialization and close functions?
374 Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
375 AVInputFormat/AVOutputFormat struct?
377 Did you bump the minor version number (and reset the micro version
378 number) in ‘<tt>avcodec.h</tt>’ or ‘<tt>avformat.h</tt>’?
380 Did you register it in ‘<tt>allcodecs.c</tt>’ or ‘<tt>allformats.c</tt>’?
382 Did you add the CodecID to ‘<tt>avcodec.h</tt>’?
384 If it has a fourcc, did you add it to ‘<tt>libavformat/riff.c</tt>’,
385 even if it is only a decoder?
387 Did you add a rule to compile the appropriate files in the Makefile?
388 Remember to do this even if you’re just adding a format to a file that is
389 already being compiled by some other rule, like a raw demuxer.
391 Did you add an entry to the table of supported formats or codecs in
392 ‘<tt>doc/general.texi</tt>’?
394 Did you add an entry in the Changelog?
396 If it depends on a parser or a library, did you add that dependency in
399 Did you <code>git add</code> the appropriate files before committing?
401 Did you make sure it compiles standalone, i.e. with
402 <code>configure --disable-everything --enable-decoder=foo</code>
403 (or <code>--enable-demuxer</code> or whatever your component is)?
407 <a name="patch-submission-checklist"></a>
408 <h2 class="section"><a href="developer.html#toc-patch-submission-checklist">1.8 patch submission checklist</a></h2>
412 Does <code>make fate</code> pass with the patch applied?
414 Was the patch generated with git format-patch or send-email?
416 Did you sign off your patch? (git commit -s)
417 See <a href="http://kerneltrap.org/files/Jeremy/DCO.txt">http://kerneltrap.org/files/Jeremy/DCO.txt</a> for the meaning
420 Did you provide a clear git commit log message?
422 Is the patch against latest FFmpeg git master branch?
424 Are you subscribed to ffmpeg-devel?
425 (the list is subscribers only due to spam)
427 Have you checked that the changes are minimal, so that the same cannot be
428 achieved with a smaller patch and/or simpler final code?
430 If the change is to speed critical code, did you benchmark it?
432 If you did any benchmarks, did you provide them in the mail?
434 Have you checked that the patch does not introduce buffer overflows or
435 other security issues?
437 Did you test your decoder or demuxer against damaged data? If no, see
438 tools/trasher and the noise bitstream filter. Your decoder or demuxer
439 should not crash or end in a (near) infinite loop when fed damaged data.
441 Does the patch not mix functional and cosmetic changes?
443 Did you add tabs or trailing whitespace to the code? Both are forbidden.
445 Is the patch attached to the email you send?
447 Is the mime type of the patch correct? It should be text/x-diff or
448 text/x-patch or at least text/plain and not application/octet-stream.
450 If the patch fixes a bug, did you provide a verbose analysis of the bug?
452 If the patch fixes a bug, did you provide enough information, including
453 a sample, so the bug can be reproduced and the fix can be verified?
454 Note please do not attach samples >100k to mails but rather provide a
455 URL, you can upload to ftp://upload.ffmpeg.org
457 Did you provide a verbose summary about what the patch does change?
459 Did you provide a verbose explanation why it changes things like it does?
461 Did you provide a verbose summary of the user visible advantages and
462 disadvantages if the patch is applied?
464 Did you provide an example so we can verify the new feature added by the
467 If you added a new file, did you insert a license header? It should be
468 taken from FFmpeg, not randomly copied and pasted from somewhere else.
470 You should maintain alphabetical order in alphabetically ordered lists as
471 long as doing so does not break API/ABI compatibility.
473 Lines with similar content should be aligned vertically when doing so
474 improves readability.
476 Consider to add a regression test for your code.
478 If you added YASM code please check that things still work with –disable-yasm
481 <a name="Patch-review-process"></a>
482 <h2 class="section"><a href="developer.html#toc-Patch-review-process">1.9 Patch review process</a></h2>
484 <p>All patches posted to ffmpeg-devel will be reviewed, unless they contain a
485 clear note that the patch is not for the git master branch.
486 Reviews and comments will be posted as replies to the patch on the
487 mailing list. The patch submitter then has to take care of every comment,
488 that can be by resubmitting a changed patch or by discussion. Resubmitted
489 patches will themselves be reviewed like any other patch. If at some point
490 a patch passes review with no comments then it is approved, that can for
491 simple and small patches happen immediately while large patches will generally
492 have to be changed and reviewed many times before they are approved.
493 After a patch is approved it will be committed to the repository.
495 <p>We will review all submitted patches, but sometimes we are quite busy so
496 especially for large patches this can take several weeks.
498 <p>If you feel that the review process is too slow and you are willing to try to
499 take over maintainership of the area of code you change then just clone
500 git master and maintain the area of code there. We will merge each area from
501 where its best maintained.
503 <p>When resubmitting patches, please do not make any significant changes
504 not related to the comments received during review. Such patches will
505 be rejected. Instead, submit significant changes or new features as
508 <a name="Regression-tests"></a>
509 <h2 class="section"><a href="developer.html#toc-Regression-tests">1.10 Regression tests</a></h2>
511 <p>Before submitting a patch (or committing to the repository), you should at least
512 test that you did not break anything.
514 <p>Running ’make fate’ accomplishes this, please see ‘<tt>doc/fate.txt</tt>’ for details.
516 <p>[Of course, some patches may change the results of the regression tests. In
517 this case, the reference results of the regression tests shall be modified
523 This document was generated by <em>Kyle Schwarz</em> on <em>September 2, 2011</em> using <a href="http://www.nongnu.org/texi2html/"><em>texi2html 1.82</em></a>.
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