Mention to send a patch before changing API or ABI.
[libav.git] / doc / developer.texi
1 \input texinfo @c -*- texinfo -*-
3 @settitle Developer Documentation
4 @titlepage
5 @sp 7
6 @center @titlefont{Developer Documentation}
7 @sp 3
8 @end titlepage
11 @chapter Developers Guide
13 @section API
14 @itemize @bullet
15 @item libavcodec is the library containing the codecs (both encoding and
16 decoding). Look at @file{libavcodec/apiexample.c} to see how to use it.
18 @item libavformat is the library containing the file format handling (mux and
19 demux code for several formats). Look at @file{ffplay.c} to use it in a
20 player. See @file{libavformat/output-example.c} to use it to generate
21 audio or video streams.
23 @end itemize
25 @section Integrating libavcodec or libavformat in your program
27 You can integrate all the source code of the libraries to link them
28 statically to avoid any version problem. All you need is to provide a
29 'config.mak' and a 'config.h' in the parent directory. See the defines
30 generated by ./configure to understand what is needed.
32 You can use libavcodec or libavformat in your commercial program, but
33 @emph{any patch you make must be published}. The best way to proceed is
34 to send your patches to the FFmpeg mailing list.
36 @anchor{Coding Rules}
37 @section Coding Rules
39 FFmpeg is programmed in the ISO C90 language with a few additional
40 features from ISO C99, namely:
41 @itemize @bullet
42 @item
43 the @samp{inline} keyword;
44 @item
45 @samp{//} comments;
46 @item
47 designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
48 @item
49 compound literals (@samp{x = (struct s) @{ 17, 23 @};})
50 @end itemize
52 These features are supported by all compilers we care about, so we will not
53 accept patches to remove their use unless they absolutely do not impair
54 clarity and performance.
56 All code must compile with GCC 2.95 and GCC 3.3. Currently, FFmpeg also
57 compiles with several other compilers, such as the Compaq ccc compiler
58 or Sun Studio 9, and we would like to keep it that way unless it would
59 be exceedingly involved. To ensure compatibility, please do not use any
60 additional C99 features or GCC extensions. Especially watch out for:
61 @itemize @bullet
62 @item
63 mixing statements and declarations;
64 @item
65 @samp{long long} (use @samp{int64_t} instead);
66 @item
67 @samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;
68 @item
69 GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
70 @end itemize
72 Indent size is 4.
73 The presentation is one inspired by 'indent -i4 -kr -nut'.
74 The TAB character is forbidden outside of Makefiles as is any
75 form of trailing whitespace. Commits containing either will be
76 rejected by the Subversion repository.
78 The main priority in FFmpeg is simplicity and small code size in order to
79 minimize the bug count.
81 Comments: Use the JavaDoc/Doxygen
82 format (see examples below) so that code documentation
83 can be generated automatically. All nontrivial functions should have a comment
84 above them explaining what the function does, even if it is just one sentence.
85 All structures and their member variables should be documented, too.
86 @example
87 /**
88 * @@file mpeg.c
89 * MPEG codec.
90 * @@author ...
91 */
93 /**
94 * Summary sentence.
95 * more text ...
96 * ...
97 */
98 typedef struct Foobar@{
99 int var1; /**< var1 description */
100 int var2; ///< var2 description
101 /** var3 description */
102 int var3;
103 @} Foobar;
105 /**
106 * Summary sentence.
107 * more text ...
108 * ...
109 * @@param my_parameter description of my_parameter
110 * @@return return value description
111 */
112 int myfunc(int my_parameter)
113 ...
114 @end example
116 fprintf and printf are forbidden in libavformat and libavcodec,
117 please use av_log() instead.
119 Casts should be used only when necessary. Unneeded parentheses
120 should also be avoided if they don't make the code easier to understand.
122 @section Development Policy
124 @enumerate
125 @item
126 Contributions should be licensed under the LGPL 2.1, including an
127 "or any later version" clause, or the MIT license. GPL 2 including
128 an "or any later version" clause is also acceptable, but LGPL is
129 preferred.
130 @item
131 You must not commit code which breaks FFmpeg! (Meaning unfinished but
132 enabled code which breaks compilation or compiles but does not work or
133 breaks the regression tests)
134 You can commit unfinished stuff (for testing etc), but it must be disabled
135 (#ifdef etc) by default so it does not interfere with other developers'
136 work.
137 @item
138 You do not have to over-test things. If it works for you, and you think it
139 should work for others, then commit. If your code has problems
140 (portability, triggers compiler bugs, unusual environment etc) they will be
141 reported and eventually fixed.
142 @item
143 Do not commit unrelated changes together, split them into self-contained
144 pieces. Also do not forget that if part B depends on part A, but A does not
145 depend on B, then A can and should be committed first and separate from B.
146 Keeping changes well split into self-contained parts makes reviewing and
147 understanding them on the commit log mailing list easier. This also helps
148 in case of debugging later on.
149 Also if you have doubts about splitting or not splitting, do not hesitate to
150 ask/discuss it on the developer mailing list.
151 @item
152 Do not change behavior of the program (renaming options etc) or public
153 API or ABI without first discussing it on the ffmpeg-devel mailing list.
154 Do not remove functionality from the code. Just improve!
156 Note: Redundant code can be removed.
157 @item
158 Do not commit changes to the build system (Makefiles, configure script)
159 which change behavior, defaults etc, without asking first. The same
160 applies to compiler warning fixes, trivial looking fixes and to code
161 maintained by other developers. We usually have a reason for doing things
162 the way we do. Send your changes as patches to the ffmpeg-devel mailing
163 list, and if the code maintainers say OK, you may commit. This does not
164 apply to files you wrote and/or maintain.
165 @item
166 We refuse source indentation and other cosmetic changes if they are mixed
167 with functional changes, such commits will be rejected and removed. Every
168 developer has his own indentation style, you should not change it. Of course
169 if you (re)write something, you can use your own style, even though we would
170 prefer if the indentation throughout FFmpeg was consistent (Many projects
171 force a given indentation style - we do not.). If you really need to make
172 indentation changes (try to avoid this), separate them strictly from real
173 changes.
175 NOTE: If you had to put if()@{ .. @} over a large (> 5 lines) chunk of code,
176 then either do NOT change the indentation of the inner part within (do not
177 move it to the right)! or do so in a separate commit
178 @item
179 Always fill out the commit log message. Describe in a few lines what you
180 changed and why. You can refer to mailing list postings if you fix a
181 particular bug. Comments such as "fixed!" or "Changed it." are unacceptable.
182 @item
183 If you apply a patch by someone else, include the name and email address in
184 the log message. Since the ffmpeg-cvslog mailing list is publicly
185 archived you should add some SPAM protection to the email address. Send an
186 answer to ffmpeg-devel (or wherever you got the patch from) saying that
187 you applied the patch.
188 @item
189 When applying patches that have been discussed (at length) on the mailing
190 list, reference the thread in the log message.
191 @item
192 Do NOT commit to code actively maintained by others without permission.
193 Send a patch to ffmpeg-devel instead. If no one answers within a reasonable
194 timeframe (12h for build failures and security fixes, 3 days small changes,
195 1 week for big patches) then commit your patch if you think it is OK.
196 Also note, the maintainer can simply ask for more time to review!
197 @item
198 Subscribe to the ffmpeg-cvslog mailing list. The diffs of all commits
199 are sent there and reviewed by all the other developers. Bugs and possible
200 improvements or general questions regarding commits are discussed there. We
201 expect you to react if problems with your code are uncovered.
202 @item
203 Update the documentation if you change behavior or add features. If you are
204 unsure how best to do this, send a patch to ffmpeg-devel, the documentation
205 maintainer(s) will review and commit your stuff.
206 @item
207 Try to keep important discussions and requests (also) on the public
208 developer mailing list, so that all developers can benefit from them.
209 @item
210 Never write to unallocated memory, never write over the end of arrays,
211 always check values read from some untrusted source before using them
212 as array index or other risky things.
213 @item
214 Remember to check if you need to bump versions for the specific libav
215 parts (libavutil, libavcodec, libavformat) you are changing. You need
216 to change the version integer.
217 Incrementing the first component means no backward compatibility to
218 previous versions (e.g. removal of a function from the public API).
219 Incrementing the second component means backward compatible change
220 (e.g. addition of a function to the public API or extension of an
221 existing data structure).
222 Incrementing the third component means a noteworthy binary compatible
223 change (e.g. encoder bug fix that matters for the decoder).
224 @item
225 Compiler warnings indicate potential bugs or code with bad style. If a type of
226 warning always points to correct and clean code, that warning should
227 be disabled, not the code changed.
228 Thus the remaining warnings can either be bugs or correct code.
229 If it is a bug, the bug has to be fixed. If it is not, the code should
230 be changed to not generate a warning unless that causes a slowdown
231 or obfuscates the code.
232 @item
233 If you add a new file, give it a proper license header. Do not copy and
234 paste it from a random place, use an existing file as template.
235 @end enumerate
237 We think our rules are not too hard. If you have comments, contact us.
239 Note, these rules are mostly borrowed from the MPlayer project.
241 @section Submitting patches
243 First, (@pxref{Coding Rules}) above if you did not yet.
245 When you submit your patch, try to send a unified diff (diff '-up'
246 option). We cannot read other diffs :-)
248 Also please do not submit a patch which contains several unrelated changes.
249 Split it into separate, self-contained pieces. This does not mean splitting
250 file by file. Instead, make the patch as small as possible while still
251 keeping it as a logical unit that contains an individual change, even
252 if it spans multiple files. This makes reviewing your patches much easier
253 for us and greatly increases your chances of getting your patch applied.
255 Use the patcheck tool of FFmpeg to check your patch.
256 The tool is located in the tools directory.
258 Run the regression tests before submitting a patch so that you can
259 verify that there are no big problems.
261 Patches should be posted as base64 encoded attachments (or any other
262 encoding which ensures that the patch will not be trashed during
263 transmission) to the ffmpeg-devel mailing list, see
264 @url{}
266 It also helps quite a bit if you tell us what the patch does (for example
267 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
268 and has no lrint()')
270 Also please if you send several patches, send each patch as a separate mail,
271 do not attach several unrelated patches to the same mail.
273 Your patch will be reviewed on the mailing list. You will likely be asked
274 to make some changes and are expected to send in an improved version that
275 incorporates the requests from the review. This process may go through
276 several iterations. Once your patch is deemed good enough, some developer
277 will pick it up and commit it to the official FFmpeg tree.
279 Give us a few days to react. But if some time passes without reaction,
280 send a reminder by email. Your patch should eventually be dealt with.
283 @section New codecs or formats checklist
285 @enumerate
286 @item
287 Did you use av_cold for codec initialization and close functions?
288 @item
289 Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
290 AVInputFormat/AVOutputFormat struct?
291 @item
292 Did you bump the minor version number (and reset the micro version
293 number) in @file{avcodec.h} or @file{avformat.h}?
294 @item
295 Did you register it in @file{allcodecs.c} or @file{allformats.c}?
296 @item
297 Did you add the CodecID to @file{avcodec.h}?
298 @item
299 If it has a fourcc, did you add it to @file{libavformat/riff.c},
300 even if it is only a decoder?
301 @item
302 Did you add a rule to compile the appropriate files in the Makefile?
303 Remember to do this even if you're just adding a format to a file that is
304 already being compiled by some other rule, like a raw demuxer.
305 @item
306 Did you add an entry to the table of supported formats or codecs in
307 @file{doc/general.texi}?
308 @item
309 Did you add an entry in the Changelog?
310 @item
311 If it depends on a parser or a library, did you add that dependency in
312 configure?
313 @item
314 Did you "svn add" the appropriate files before commiting?
315 @end enumerate
317 @section patch submission checklist
319 @enumerate
320 @item
321 Do the regression tests pass with the patch applied?
322 @item
323 Does @code{make checkheaders} pass with the patch applied?
324 @item
325 Is the patch a unified diff?
326 @item
327 Is the patch against latest FFmpeg SVN?
328 @item
329 Are you subscribed to ffmpeg-dev?
330 (the list is subscribers only due to spam)
331 @item
332 Have you checked that the changes are minimal, so that the same cannot be
333 achieved with a smaller patch and/or simpler final code?
334 @item
335 If the change is to speed critical code, did you benchmark it?
336 @item
337 If you did any benchmarks, did you provide them in the mail?
338 @item
339 Have you checked that the patch does not introduce buffer overflows or
340 other security issues?
341 @item
342 Did you test your decoder or demuxer against damaged data? If no, see
343 tools/trasher and the noise bitstream filter. Your decoder or demuxer
344 should not crash or end in a (near) infinite loop when fed damaged data.
345 @item
346 Is the patch created from the root of the source tree, so it can be
347 applied with @code{patch -p0}?
348 @item
349 Does the patch not mix functional and cosmetic changes?
350 @item
351 Did you add tabs or trailing whitespace to the code? Both are forbidden.
352 @item
353 Is the patch attached to the email you send?
354 @item
355 Is the mime type of the patch correct? It should be text/x-diff or
356 text/x-patch or at least text/plain and not application/octet-stream.
357 @item
358 If the patch fixes a bug, did you provide a verbose analysis of the bug?
359 @item
360 If the patch fixes a bug, did you provide enough information, including
361 a sample, so the bug can be reproduced and the fix can be verified?
362 Note please do not attach samples >100k to mails but rather provide a
363 URL, you can upload to
364 @item
365 Did you provide a verbose summary about what the patch does change?
366 @item
367 Did you provide a verbose explanation why it changes things like it does?
368 @item
369 Did you provide a verbose summary of the user visible advantages and
370 disadvantages if the patch is applied?
371 @item
372 Did you provide an example so we can verify the new feature added by the
373 patch easily?
374 @item
375 If you added a new file, did you insert a license header? It should be
376 taken from FFmpeg, not randomly copied and pasted from somewhere else.
377 @item
378 You should maintain alphabetical order in alphabetically ordered lists as
379 long as doing so does not break API/ABI compatibility.
380 @item
381 Lines with similar content should be aligned vertically when doing so
382 improves readability.
383 @item
384 Did you provide a suggestion for a clear commit log message?
385 @end enumerate
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 SVN.
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
406 separate patches.
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
418 has run.
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
422 as well.
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
428 'make V=2 test'.
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
434 accordingly].
436 @bye