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 libav in your program
28 Shared libraries should be used whenever is possible in order to reduce
29 the effort distributors have to pour to support programs and to ensure
30 only the public api is used.
32 You can use Libav in your commercial program, but you must abide to the
33 license, LGPL or GPL depending on the specific features used, please refer
34 to @url{http://libav.org/legal.html} for a quick checklist and to
35 @url{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.GPLv2},
36 @url{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.GPLv3},
37 @url{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.LGPLv2.1},
38 @url{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.LGPLv3} for the
39 exact text of the licenses.
40 Any modification to the source code can be suggested for inclusion.
41 The best way to proceed is to send your patches to the Libav mailing list.
46 Libav is programmed in the ISO C90 language with a few additional
47 features from ISO C99, namely:
50 the @samp{inline} keyword;
54 designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
56 compound literals (@samp{x = (struct s) @{ 17, 23 @};})
59 These features are supported by all compilers we care about, so we will not
60 accept patches to remove their use unless they absolutely do not impair
61 clarity and performance.
63 All code must compile with GCC 2.95 and GCC 3.3. Currently, Libav also
64 compiles with several other compilers, such as the Compaq ccc compiler
65 or Sun Studio 9, and we would like to keep it that way unless it would
66 be exceedingly involved. To ensure compatibility, please do not use any
67 additional C99 features or GCC extensions. Especially watch out for:
70 mixing statements and declarations;
72 @samp{long long} (use @samp{int64_t} instead);
74 @samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;
76 GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
80 The presentation is one inspired by 'indent -i4 -kr -nut'.
81 The TAB character is forbidden outside of Makefiles as is any
82 form of trailing whitespace. Commits containing either will be
83 rejected by the git repository.
85 The main priority in Libav is simplicity and small code size in order to
86 minimize the bug count.
88 Comments: Use the JavaDoc/Doxygen
89 format (see examples below) so that code documentation
90 can be generated automatically. All nontrivial functions should have a comment
91 above them explaining what the function does, even if it is just one sentence.
92 All structures and their member variables should be documented, too.
105 typedef struct Foobar@{
106 int var1; /**< var1 description */
107 int var2; ///< var2 description
108 /** var3 description */
116 * @@param my_parameter description of my_parameter
117 * @@return return value description
119 int myfunc(int my_parameter)
123 fprintf and printf are forbidden in libavformat and libavcodec,
124 please use av_log() instead.
126 Casts should be used only when necessary. Unneeded parentheses
127 should also be avoided if they don't make the code easier to understand.
129 @section Development Policy
133 Contributions should be licensed under the LGPL 2.1, including an
134 "or any later version" clause, or the MIT license. GPL 2 including
135 an "or any later version" clause is also acceptable, but LGPL is
138 All the patches MUST be reviewed in the mailing list before they are
141 The Libav coding style should remain consistent. Changes to
142 conform will be suggested during the review or implemented on commit.
144 Patches should be generated using @code{git format-patch} or directly sent
145 using @code{git send-email}.
146 Please make sure you give the proper credit by setting the correct author
149 The commit message should have a short first line in the form of
150 @samp{topic: short description} as header, separated by a newline
151 from the body consting in few lines explaining the reason of the patch.
152 Referring to the issue on the bug tracker does not exempt to report an
155 Work in progress patches should be sent to the mailing list with the [WIP]
158 Branches in public personal repos are advised as way to
159 work on issues collaboratively.
161 You do not have to over-test things. If it works for you and you think it
162 should work for others, send it to the mailing list for review.
163 If you have doubt about portability please state it in the submission so
164 people with specific hardware could test it.
166 Do not commit unrelated changes together, split them into self-contained
167 pieces. Also do not forget that if part B depends on part A, but A does not
168 depend on B, then A can and should be committed first and separate from B.
169 Keeping changes well split into self-contained parts makes reviewing and
170 understanding them on the commit log mailing list easier. This also helps
171 in case of debugging later on.
173 Patches that change behavior of the programs (renaming options etc) or
174 public API or ABI should be discussed in depth and possible few days should
175 pass between discussion and commit.
176 Changes to the build system (Makefiles, configure script) which alter
177 the expected behavior should be considered in the same regard.
179 When applying patches that have been discussed (at length) on the mailing
180 list, reference the thread in the log message.
182 Subscribe to the libav-devel and libav-commits mailing list.
183 Bugs and possible improvements or general questions regarding commits
184 are discussed on libav-devel. We expect you to react if problems with
185 your code are uncovered.
187 Update the documentation if you change behavior or add features. If you are
188 unsure how best to do this, send an [RFC] patch to libav-devel.
190 All discussions and decisions should be reported on the public developer
191 mailing list, so that there is a reference to them.
192 Other media (e.g. IRC) should be used for coordination and immediate
195 Never write to unallocated memory, never write over the end of arrays,
196 always check values read from some untrusted source before using them
197 as array index or other risky things. Always use valgrind to doublecheck.
199 Remember to check if you need to bump versions for the specific libav
200 parts (libavutil, libavcodec, libavformat) you are changing. You need
201 to change the version integer.
202 Incrementing the first component means no backward compatibility to
203 previous versions (e.g. removal of a function from the public API).
204 Incrementing the second component means backward compatible change
205 (e.g. addition of a function to the public API or extension of an
206 existing data structure).
207 Incrementing the third component means a noteworthy binary compatible
208 change (e.g. encoder bug fix that matters for the decoder).
210 Compiler warnings indicate potential bugs or code with bad style.
211 If it is a bug, the bug has to be fixed. If it is not, the code should
212 be changed to not generate a warning unless that causes a slowdown
213 or obfuscates the code.
214 If a type of warning leads to too many false positives, that warning
215 should be disabled, not the code changed.
217 If you add a new file, give it a proper license header. Do not copy and
218 paste it from a random place, use an existing file as template.
221 We think our rules are not too hard. If you have comments, contact us.
223 Note, some rules were borrowed from the MPlayer project.
225 @section Submitting patches
227 First, read the (@pxref{Coding Rules}) above if you did not yet, in particular
228 the rules regarding patch submission.
230 As stated already, please do not submit a patch which contains several
232 Split it into separate, self-contained pieces. This does not mean splitting
233 file by file. Instead, make the patch as small as possible while still
234 keeping it as a logical unit that contains an individual change, even
235 if it spans multiple files. This makes reviewing your patches much easier
236 for us and greatly increases your chances of getting your patch applied.
238 Use the patcheck tool of Libav to check your patch.
239 The tool is located in the tools directory.
241 Run the @pxref{Regression Tests} before submitting a patch in order to verify
242 it does not cause unexpected problems.
244 Patches should be posted as base64 encoded attachments (or any other
245 encoding which ensures that the patch will not be trashed during
246 transmission) to the libav-devel mailing list, see
247 @url{https://lists.libav.org/mailman/listinfo/libav-devel}
249 It also helps quite a bit if you tell us what the patch does (for example
250 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
251 and has no lrint()'). This kind of explanation should be the body of the
254 Also please if you send several patches, send each patch as a separate mail,
255 do not attach several unrelated patches to the same mail.
257 Use @code{git send-email} when possible since it will properly send patches
258 without requiring extra care.
260 Your patch will be reviewed on the mailing list. You will likely be asked
261 to make some changes and are expected to send in an improved version that
262 incorporates the requests from the review. This process may go through
263 several iterations. Once your patch is deemed good enough, it will be
264 committed to the official Libav tree.
266 Give us a few days to react. But if some time passes without reaction,
267 send a reminder by email. Your patch should eventually be dealt with.
270 @section New codecs or formats checklist
274 Did you use av_cold for codec initialization and close functions?
276 Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
277 AVInputFormat/AVOutputFormat struct?
279 Did you bump the minor version number (and reset the micro version
280 number) in @file{avcodec.h} or @file{avformat.h}?
282 Did you register it in @file{allcodecs.c} or @file{allformats.c}?
284 Did you add the CodecID to @file{avcodec.h}?
286 If it has a fourcc, did you add it to @file{libavformat/riff.c},
287 even if it is only a decoder?
289 Did you add a rule to compile the appropriate files in the Makefile?
290 Remember to do this even if you are just adding a format to a file that
291 is already being compiled by some other rule, like a raw demuxer.
293 Did you add an entry to the table of supported formats or codecs in
294 @file{doc/general.texi}?
296 Did you add an entry in the Changelog?
298 If it depends on a parser or a library, did you add that dependency in
301 Did you @code{git add} the appropriate files before committing?
303 Did you make sure it compiles standalone, i.e. with
304 @code{configure --disable-everything --enable-decoder=foo}
305 (or @code{--enable-demuxer} or whatever your component is)?
309 @section patch submission checklist
313 Do the regression tests pass with the patch applied?
315 Does @code{make checkheaders} pass with the patch applied?
317 Is the patch against latest Libav git master branch?
319 Are you subscribed to libav-devel?
320 (@url{https://lists.libav.org/mailman/listinfo/libav-devel}
321 the list is subscribers)
323 Have you checked that the changes are minimal, so that the same cannot be
324 achieved with a smaller patch and/or simpler final code?
326 If the change is to speed critical code, did you benchmark it?
328 If you did any benchmarks, did you provide them in the mail?
330 Have you checked that the patch does not introduce buffer overflows or
331 other security issues?
333 Did you test your decoder or demuxer against damaged data? If no, see
334 tools/trasher and the noise bitstream filter. Your decoder or demuxer
335 should not crash or end in a (near) infinite loop when fed damaged data.
337 Does the patch not mix functional and cosmetic changes?
339 Did you add tabs or trailing whitespace to the code? Both are forbidden.
341 Is the patch attached to the email you send?
343 Is the mime type of the patch correct? It should be text/x-diff or
344 text/x-patch or at least text/plain and not application/octet-stream.
346 If the patch fixes a bug, did you provide a verbose analysis of the bug?
348 If the patch fixes a bug, did you provide enough information, including
349 a sample, so the bug can be reproduced and the fix can be verified?
350 Note please do not attach samples >100k to mails but rather provide a
351 URL, you can upload to ftp://upload.libav.org
353 Did you provide a verbose summary about what the patch does change?
355 Did you provide a verbose explanation why it changes things like it does?
357 Did you provide a verbose summary of the user visible advantages and
358 disadvantages if the patch is applied?
360 Did you provide an example so we can verify the new feature added by the
363 If you added a new file, did you insert a license header? It should be
364 taken from Libav, not randomly copied and pasted from somewhere else.
366 You should maintain alphabetical order in alphabetically ordered lists as
367 long as doing so does not break API/ABI compatibility.
369 Lines with similar content should be aligned vertically when doing so
370 improves readability.
373 @section Patch review process
375 All patches posted to libav-devel will be reviewed, unless they contain a
376 clear note that the patch is not for the git master branch.
377 Reviews and comments will be posted as replies to the patch on the
378 mailing list. The patch submitter then has to take care of every comment,
379 that can be by resubmitting a changed patch or by discussion. Resubmitted
380 patches will themselves be reviewed like any other patch. If at some point
381 a patch passes review with no comments then it is approved, that can for
382 simple and small patches happen immediately while large patches will generally
383 have to be changed and reviewed many times before they are approved.
384 After a patch is approved it will be committed to the repository.
386 We will review all submitted patches, but sometimes we are quite busy so
387 especially for large patches this can take several weeks.
389 When resubmitting patches, if their size grew or during the review different
390 issues arisen please split the patch so each issue has a specific patch.
392 @anchor{Regression Tests}
393 @section Regression Tests
395 Before submitting a patch (or committing to the repository), you should at
396 least make sure that it does not break anything.
398 If the code changed has already a test present in FATE you should run it,
399 otherwise it is advised to add it.
401 Improvements to codec or demuxer might change the FATE results. Make sure
402 to commit the update reference with the change and to explain in the comment
403 why the expected result changed.
405 Please refer to @file{doc/fate.txt}.