[libav.git] / doc / developer.texi
1 \input texinfo @c -*- texinfo -*-
3 @settitle Developer Documentation
4 @titlepage
5 @center @titlefont{Developer Documentation}
6 @end titlepage
8 @top
10 @contents
12 @chapter Developers Guide
14 @section API
15 @itemize @bullet
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{avplay.c} to use it in a
21 player. See @file{libavformat/output-example.c} to use it to generate
22 audio or video streams.
24 @end itemize
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 @uref{http://libav.org/legal.html, our legal page} for a quick checklist and to
35 the following links for the exact text of each license:
36 @uref{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.GPLv2, GPL version 2},
37 @uref{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.GPLv3, GPL version 3},
38 @uref{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.LGPLv2.1, LGPL version 2.1},
39 @uref{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.LGPLv3, LGPL version 3}.
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
42 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
43 mailing list.
45 @anchor{Coding Rules}
46 @section Coding Rules
48 @subsection Code formatting conventions
49 The code is written in K&R C style. That means the following:
50 @itemize @bullet
51 @item
52 The control statements are formatted by putting space betwen the statement
53 and parenthesis in the following way:
54 @example
55 for (i = 0; i < filter->input_count; i++) @{
56 @end example
57 @item
58 The case statement is always located at the same level as the switch itself:
59 @example
60 switch (link->init_state) @{
61 case AVLINK_INIT:
62 continue;
64 av_log(filter, AV_LOG_INFO, "circular filter chain detected");
65 return 0;
66 @end example
67 @item
68 Braces in function declarations are written on the new line:
69 @example
70 const char *avfilter_configuration(void)
71 @{
73 @}
74 @end example
75 @item
76 In case of a single-statement if, no curly braces are required:
77 @example
78 if (!pic || !picref)
79 goto fail;
80 @end example
81 @item
82 Do not put spaces immediately inside parenthesis. @samp{if (ret)} is
83 a valid style; @samp{if ( ret )} is not.
84 @end itemize
86 There are the following guidelines regarding the indentation in files:
87 @itemize @bullet
88 @item
89 Indent size is 4.
90 @item
91 The TAB character is forbidden outside of Makefiles as is any
92 form of trailing whitespace. Commits containing either will be
93 rejected by the git repository.
94 @item
95 You should try to limit your code lines to 80 characters; however, do so if
96 and only if this improves readability.
97 @end itemize
98 The presentation is one inspired by 'indent -i4 -kr -nut'.
100 The main priority in Libav is simplicity and small code size in order to
101 minimize the bug count.
103 @subsection Comments
104 Use the JavaDoc/Doxygen format (see examples below) so that code documentation
105 can be generated automatically. All nontrivial functions should have a comment
106 above them explaining what the function does, even if it is just one sentence.
107 All structures and their member variables should be documented, too.
109 Avoid Qt-style and similar Doxygen syntax with @code{!} in it, i.e. replace
110 @code{//!} with @code{///} and similar. Also @@ syntax should be employed
111 for markup commands, i.e. use @code{@@param} and not @code{\param}.
113 @example
114 /**
115 * @@file
116 * MPEG codec.
117 * @@author ...
118 */
120 /**
121 * Summary sentence.
122 * more text ...
123 * ...
124 */
125 typedef struct Foobar@{
126 int var1; /**< var1 description */
127 int var2; ///< var2 description
128 /** var3 description */
129 int var3;
130 @} Foobar;
132 /**
133 * Summary sentence.
134 * more text ...
135 * ...
136 * @@param my_parameter description of my_parameter
137 * @@return return value description
138 */
139 int myfunc(int my_parameter)
140 ...
141 @end example
143 @subsection C language features
145 Libav is programmed in the ISO C90 language with a few additional
146 features from ISO C99, namely:
147 @itemize @bullet
148 @item
149 the @samp{inline} keyword;
150 @item
151 @samp{//} comments;
152 @item
153 designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
154 @item
155 compound literals (@samp{x = (struct s) @{ 17, 23 @};})
156 @end itemize
158 These features are supported by all compilers we care about, so we will not
159 accept patches to remove their use unless they absolutely do not impair
160 clarity and performance.
162 All code must compile with recent versions of GCC and a number of other
163 currently supported compilers. To ensure compatibility, please do not use
164 additional C99 features or GCC extensions. Especially watch out for:
165 @itemize @bullet
166 @item
167 mixing statements and declarations;
168 @item
169 @samp{long long} (use @samp{int64_t} instead);
170 @item
171 @samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;
172 @item
173 GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
174 @end itemize
176 @subsection Naming conventions
177 All names are using underscores (_), not CamelCase. For example,
178 @samp{avfilter_get_video_buffer} is a valid function name and
179 @samp{AVFilterGetVideo} is not. The only exception from this are structure
180 names; they should always be in the CamelCase
182 There are following conventions for naming variables and functions:
183 @itemize @bullet
184 @item
185 For local variables no prefix is required.
186 @item
187 For variables and functions declared as @code{static} no prefixes are required.
188 @item
189 For variables and functions used internally by the library, @code{ff_} prefix
190 should be used.
191 For example, @samp{ff_w64_demuxer}.
192 @item
193 For variables and functions used internally across multiple libraries, use
194 @code{avpriv_}. For example, @samp{avpriv_aac_parse_header}.
195 @item
196 For exported names, each library has its own prefixes. Just check the existing
197 code and name accordingly.
198 @end itemize
200 @subsection Miscellanous conventions
201 @itemize @bullet
202 @item
203 fprintf and printf are forbidden in libavformat and libavcodec,
204 please use av_log() instead.
205 @item
206 Casts should be used only when necessary. Unneeded parentheses
207 should also be avoided if they don't make the code easier to understand.
208 @end itemize
210 @section Development Policy
212 @enumerate
213 @item
214 Contributions should be licensed under the LGPL 2.1, including an
215 "or any later version" clause, or the MIT license. GPL 2 including
216 an "or any later version" clause is also acceptable, but LGPL is
217 preferred.
218 @item
219 All the patches MUST be reviewed in the mailing list before they are
220 committed.
221 @item
222 The Libav coding style should remain consistent. Changes to
223 conform will be suggested during the review or implemented on commit.
224 @item
225 Patches should be generated using @code{git format-patch} or directly sent
226 using @code{git send-email}.
227 Please make sure you give the proper credit by setting the correct author
228 in the commit.
229 @item
230 The commit message should have a short first line in the form of
231 @samp{topic: short description} as header, separated by a newline
232 from the body consting in few lines explaining the reason of the patch.
233 Referring to the issue on the bug tracker does not exempt to report an
234 excerpt of the bug.
235 @item
236 Work in progress patches should be sent to the mailing list with the [WIP]
237 or the [RFC] tag.
238 @item
239 Branches in public personal repos are advised as way to
240 work on issues collaboratively.
241 @item
242 You do not have to over-test things. If it works for you and you think it
243 should work for others, send it to the mailing list for review.
244 If you have doubt about portability please state it in the submission so
245 people with specific hardware could test it.
246 @item
247 Do not commit unrelated changes together, split them into self-contained
248 pieces. Also do not forget that if part B depends on part A, but A does not
249 depend on B, then A can and should be committed first and separate from B.
250 Keeping changes well split into self-contained parts makes reviewing and
251 understanding them on the commit log mailing list easier. This also helps
252 in case of debugging later on.
253 @item
254 Patches that change behavior of the programs (renaming options etc) or
255 public API or ABI should be discussed in depth and possible few days should
256 pass between discussion and commit.
257 Changes to the build system (Makefiles, configure script) which alter
258 the expected behavior should be considered in the same regard.
259 @item
260 When applying patches that have been discussed (at length) on the mailing
261 list, reference the thread in the log message.
262 @item
263 Subscribe to the
264 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel} and
265 @uref{https://lists.libav.org/mailman/listinfo/libav-commits, libav-commits}
266 mailing lists.
267 Bugs and possible improvements or general questions regarding commits
268 are discussed on libav-devel. We expect you to react if problems with
269 your code are uncovered.
270 @item
271 Update the documentation if you change behavior or add features. If you are
272 unsure how best to do this, send an [RFC] patch to libav-devel.
273 @item
274 All discussions and decisions should be reported on the public developer
275 mailing list, so that there is a reference to them.
276 Other media (e.g. IRC) should be used for coordination and immediate
277 collaboration.
278 @item
279 Never write to unallocated memory, never write over the end of arrays,
280 always check values read from some untrusted source before using them
281 as array index or other risky things. Always use valgrind to doublecheck.
282 @item
283 Remember to check if you need to bump versions for the specific libav
284 parts (libavutil, libavcodec, libavformat) you are changing. You need
285 to change the version integer.
286 Incrementing the first component means no backward compatibility to
287 previous versions (e.g. removal of a function from the public API).
288 Incrementing the second component means backward compatible change
289 (e.g. addition of a function to the public API or extension of an
290 existing data structure).
291 Incrementing the third component means a noteworthy binary compatible
292 change (e.g. encoder bug fix that matters for the decoder).
293 @item
294 Compiler warnings indicate potential bugs or code with bad style.
295 If it is a bug, the bug has to be fixed. If it is not, the code should
296 be changed to not generate a warning unless that causes a slowdown
297 or obfuscates the code.
298 If a type of warning leads to too many false positives, that warning
299 should be disabled, not the code changed.
300 @item
301 If you add a new file, give it a proper license header. Do not copy and
302 paste it from a random place, use an existing file as template.
303 @end enumerate
305 We think our rules are not too hard. If you have comments, contact us.
307 Note, some rules were borrowed from the MPlayer project.
309 @section Submitting patches
311 First, read the @ref{Coding Rules} above if you did not yet, in particular
312 the rules regarding patch submission.
314 As stated already, please do not submit a patch which contains several
315 unrelated changes.
316 Split it into separate, self-contained pieces. This does not mean splitting
317 file by file. Instead, make the patch as small as possible while still
318 keeping it as a logical unit that contains an individual change, even
319 if it spans multiple files. This makes reviewing your patches much easier
320 for us and greatly increases your chances of getting your patch applied.
322 Use the patcheck tool of Libav to check your patch.
323 The tool is located in the tools directory.
325 Run the @ref{Regression Tests} before submitting a patch in order to verify
326 it does not cause unexpected problems.
328 Patches should be posted as base64 encoded attachments (or any other
329 encoding which ensures that the patch will not be trashed during
330 transmission) to the
331 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
332 mailing list.
334 It also helps quite a bit if you tell us what the patch does (for example
335 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
336 and has no lrint()'). This kind of explanation should be the body of the
337 commit message.
339 Also please if you send several patches, send each patch as a separate mail,
340 do not attach several unrelated patches to the same mail.
342 Use @code{git send-email} when possible since it will properly send patches
343 without requiring extra care.
345 Your patch will be reviewed on the mailing list. You will likely be asked
346 to make some changes and are expected to send in an improved version that
347 incorporates the requests from the review. This process may go through
348 several iterations. Once your patch is deemed good enough, it will be
349 committed to the official Libav tree.
351 Give us a few days to react. But if some time passes without reaction,
352 send a reminder by email. Your patch should eventually be dealt with.
355 @section New codecs or formats checklist
357 @enumerate
358 @item
359 Did you use av_cold for codec initialization and close functions?
360 @item
361 Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
362 AVInputFormat/AVOutputFormat struct?
363 @item
364 Did you bump the minor version number (and reset the micro version
365 number) in @file{libavcodec/version.h} or @file{libavformat/version.h}?
366 @item
367 Did you register it in @file{allcodecs.c} or @file{allformats.c}?
368 @item
369 Did you add the CodecID to @file{avcodec.h}?
370 @item
371 If it has a fourcc, did you add it to @file{libavformat/riff.c},
372 even if it is only a decoder?
373 @item
374 Did you add a rule to compile the appropriate files in the Makefile?
375 Remember to do this even if you are just adding a format to a file that
376 is already being compiled by some other rule, like a raw demuxer.
377 @item
378 Did you add an entry to the table of supported formats or codecs in
379 @file{doc/general.texi}?
380 @item
381 Did you add an entry in the Changelog?
382 @item
383 If it depends on a parser or a library, did you add that dependency in
384 configure?
385 @item
386 Did you @code{git add} the appropriate files before committing?
387 @item
388 Did you make sure it compiles standalone, i.e. with
389 @code{configure --disable-everything --enable-decoder=foo}
390 (or @code{--enable-demuxer} or whatever your component is)?
391 @end enumerate
394 @section patch submission checklist
396 @enumerate
397 @item
398 Does @code{make fate} pass with the patch applied?
399 @item
400 Does @code{make checkheaders} pass with the patch applied?
401 @item
402 Is the patch against latest Libav git master branch?
403 @item
404 Are you subscribed to the
405 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
406 mailing list? (Only list subscribers are allowed to post.)
407 @item
408 Have you checked that the changes are minimal, so that the same cannot be
409 achieved with a smaller patch and/or simpler final code?
410 @item
411 If the change is to speed critical code, did you benchmark it?
412 @item
413 If you did any benchmarks, did you provide them in the mail?
414 @item
415 Have you checked that the patch does not introduce buffer overflows or
416 other security issues?
417 @item
418 Did you test your decoder or demuxer against damaged data? If no, see
419 tools/trasher and the noise bitstream filter. Your decoder or demuxer
420 should not crash or end in a (near) infinite loop when fed damaged data.
421 @item
422 Does the patch not mix functional and cosmetic changes?
423 @item
424 Did you add tabs or trailing whitespace to the code? Both are forbidden.
425 @item
426 Is the patch attached to the email you send?
427 @item
428 Is the mime type of the patch correct? It should be text/x-diff or
429 text/x-patch or at least text/plain and not application/octet-stream.
430 @item
431 If the patch fixes a bug, did you provide a verbose analysis of the bug?
432 @item
433 If the patch fixes a bug, did you provide enough information, including
434 a sample, so the bug can be reproduced and the fix can be verified?
435 Note please do not attach samples >100k to mails but rather provide a
436 URL, you can upload to ftp://upload.libav.org
437 @item
438 Did you provide a verbose summary about what the patch does change?
439 @item
440 Did you provide a verbose explanation why it changes things like it does?
441 @item
442 Did you provide a verbose summary of the user visible advantages and
443 disadvantages if the patch is applied?
444 @item
445 Did you provide an example so we can verify the new feature added by the
446 patch easily?
447 @item
448 If you added a new file, did you insert a license header? It should be
449 taken from Libav, not randomly copied and pasted from somewhere else.
450 @item
451 You should maintain alphabetical order in alphabetically ordered lists as
452 long as doing so does not break API/ABI compatibility.
453 @item
454 Lines with similar content should be aligned vertically when doing so
455 improves readability.
456 @end enumerate
458 @section Patch review process
460 All patches posted to the
461 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
462 mailing list will be reviewed, unless they contain a
463 clear note that the patch is not for the git master branch.
464 Reviews and comments will be posted as replies to the patch on the
465 mailing list. The patch submitter then has to take care of every comment,
466 that can be by resubmitting a changed patch or by discussion. Resubmitted
467 patches will themselves be reviewed like any other patch. If at some point
468 a patch passes review with no comments then it is approved, that can for
469 simple and small patches happen immediately while large patches will generally
470 have to be changed and reviewed many times before they are approved.
471 After a patch is approved it will be committed to the repository.
473 We will review all submitted patches, but sometimes we are quite busy so
474 especially for large patches this can take several weeks.
476 When resubmitting patches, if their size grew or during the review different
477 issues arisen please split the patch so each issue has a specific patch.
479 @anchor{Regression Tests}
480 @section Regression Tests
482 Before submitting a patch (or committing to the repository), you should at
483 least make sure that it does not break anything.
485 If the code changed has already a test present in FATE you should run it,
486 otherwise it is advised to add it.
488 Improvements to codec or demuxer might change the FATE results. Make sure
489 to commit the update reference with the change and to explain in the comment
490 why the expected result changed.
492 Please refer to @file{doc/fate.txt}.
494 @bye