e484520413d4c54b26dc3194d235bdc56b99b30b
[libav.git] / doc / developer.texi
1 \input texinfo @c -*- texinfo -*-
2
3 @settitle Developer Documentation
4 @titlepage
5 @center @titlefont{Developer Documentation}
6 @end titlepage
7
8 @top
9
10 @contents
11
12 @chapter Developers Guide
13
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.
18
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.
23
24 @end itemize
25
26 @section Integrating libav in your program
27
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.
31
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.
44
45 @anchor{Coding Rules}
46 @section Coding Rules
47
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 between 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;
63 case AVLINK_STARTINIT:
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 @{
72 return LIBAV_CONFIGURATION;
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 parentheses. @samp{if (ret)} is
83 a valid style; @samp{if ( ret )} is not.
84 @end itemize
85
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'.
99
100 The main priority in Libav is simplicity and small code size in order to
101 minimize the bug count.
102
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.
108
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}.
112
113 @example
114 /**
115 * @@file
116 * MPEG codec.
117 * @@author ...
118 */
119
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;
131
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
142
143 @subsection C language features
144
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
157
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.
161
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
175
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
181
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
199
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
209
210 @subsection Editor configuration
211 In order to configure Vim to follow Libav formatting conventions, paste
212 the following snippet into your @file{.vimrc}:
213 @example
214 " indentation rules for libav: 4 spaces, no tabs
215 set expandtab
216 set shiftwidth=4
217 set softtabstop=4
218 " allow tabs in Makefiles
219 autocmd FileType make set noexpandtab shiftwidth=8 softtabstop=8
220 " Trailing whitespace and tabs are forbidden, so highlight them.
221 highlight ForbiddenWhitespace ctermbg=red guibg=red
222 match ForbiddenWhitespace /\s\+$\|\t/
223 " Do not highlight spaces at the end of line while typing on that line.
224 autocmd InsertEnter * match ForbiddenWhitespace /\t\|\s\+\%#\@@<!$/
225 @end example
226
227 For Emacs, add these roughly equivalent lines to your @file{.emacs.d/init.el}:
228 @example
229 (setq c-default-style "k&r")
230 (setq-default c-basic-offset 4)
231 (setq-default indent-tabs-mode nil)
232 (setq-default show-trailing-whitespace t)
233 @end example
234
235 @section Development Policy
236
237 @enumerate
238 @item
239 Contributions should be licensed under the LGPL 2.1, including an
240 "or any later version" clause, or the MIT license. GPL 2 including
241 an "or any later version" clause is also acceptable, but LGPL is
242 preferred.
243 @item
244 All the patches MUST be reviewed in the mailing list before they are
245 committed.
246 @item
247 The Libav coding style should remain consistent. Changes to
248 conform will be suggested during the review or implemented on commit.
249 @item
250 Patches should be generated using @code{git format-patch} or directly sent
251 using @code{git send-email}.
252 Please make sure you give the proper credit by setting the correct author
253 in the commit.
254 @item
255 The commit message should have a short first line in the form of
256 @samp{topic: short description} as header, separated by a newline
257 from the body consting in few lines explaining the reason of the patch.
258 Referring to the issue on the bug tracker does not exempt to report an
259 excerpt of the bug.
260 @item
261 Work in progress patches should be sent to the mailing list with the [WIP]
262 or the [RFC] tag.
263 @item
264 Branches in public personal repos are advised as way to
265 work on issues collaboratively.
266 @item
267 You do not have to over-test things. If it works for you and you think it
268 should work for others, send it to the mailing list for review.
269 If you have doubt about portability please state it in the submission so
270 people with specific hardware could test it.
271 @item
272 Do not commit unrelated changes together, split them into self-contained
273 pieces. Also do not forget that if part B depends on part A, but A does not
274 depend on B, then A can and should be committed first and separate from B.
275 Keeping changes well split into self-contained parts makes reviewing and
276 understanding them on the commit log mailing list easier. This also helps
277 in case of debugging later on.
278 @item
279 Patches that change behavior of the programs (renaming options etc) or
280 public API or ABI should be discussed in depth and possible few days should
281 pass between discussion and commit.
282 Changes to the build system (Makefiles, configure script) which alter
283 the expected behavior should be considered in the same regard.
284 @item
285 When applying patches that have been discussed (at length) on the mailing
286 list, reference the thread in the log message.
287 @item
288 Subscribe to the
289 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel} and
290 @uref{https://lists.libav.org/mailman/listinfo/libav-commits, libav-commits}
291 mailing lists.
292 Bugs and possible improvements or general questions regarding commits
293 are discussed on libav-devel. We expect you to react if problems with
294 your code are uncovered.
295 @item
296 Update the documentation if you change behavior or add features. If you are
297 unsure how best to do this, send an [RFC] patch to libav-devel.
298 @item
299 All discussions and decisions should be reported on the public developer
300 mailing list, so that there is a reference to them.
301 Other media (e.g. IRC) should be used for coordination and immediate
302 collaboration.
303 @item
304 Never write to unallocated memory, never write over the end of arrays,
305 always check values read from some untrusted source before using them
306 as array index or other risky things. Always use valgrind to doublecheck.
307 @item
308 Remember to check if you need to bump versions for the specific libav
309 parts (libavutil, libavcodec, libavformat) you are changing. You need
310 to change the version integer.
311 Incrementing the first component means no backward compatibility to
312 previous versions (e.g. removal of a function from the public API).
313 Incrementing the second component means backward compatible change
314 (e.g. addition of a function to the public API or extension of an
315 existing data structure).
316 Incrementing the third component means a noteworthy binary compatible
317 change (e.g. encoder bug fix that matters for the decoder).
318 @item
319 Compiler warnings indicate potential bugs or code with bad style.
320 If it is a bug, the bug has to be fixed. If it is not, the code should
321 be changed to not generate a warning unless that causes a slowdown
322 or obfuscates the code.
323 If a type of warning leads to too many false positives, that warning
324 should be disabled, not the code changed.
325 @item
326 If you add a new file, give it a proper license header. Do not copy and
327 paste it from a random place, use an existing file as template.
328 @end enumerate
329
330 We think our rules are not too hard. If you have comments, contact us.
331
332 Note, some rules were borrowed from the MPlayer project.
333
334 @section Submitting patches
335
336 First, read the @ref{Coding Rules} above if you did not yet, in particular
337 the rules regarding patch submission.
338
339 As stated already, please do not submit a patch which contains several
340 unrelated changes.
341 Split it into separate, self-contained pieces. This does not mean splitting
342 file by file. Instead, make the patch as small as possible while still
343 keeping it as a logical unit that contains an individual change, even
344 if it spans multiple files. This makes reviewing your patches much easier
345 for us and greatly increases your chances of getting your patch applied.
346
347 Use the patcheck tool of Libav to check your patch.
348 The tool is located in the tools directory.
349
350 Run the @ref{Regression Tests} before submitting a patch in order to verify
351 it does not cause unexpected problems.
352
353 Patches should be posted as base64 encoded attachments (or any other
354 encoding which ensures that the patch will not be trashed during
355 transmission) to the
356 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
357 mailing list.
358
359 It also helps quite a bit if you tell us what the patch does (for example
360 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
361 and has no lrint()'). This kind of explanation should be the body of the
362 commit message.
363
364 Also please if you send several patches, send each patch as a separate mail,
365 do not attach several unrelated patches to the same mail.
366
367 Use @code{git send-email} when possible since it will properly send patches
368 without requiring extra care.
369
370 Your patch will be reviewed on the mailing list. You will likely be asked
371 to make some changes and are expected to send in an improved version that
372 incorporates the requests from the review. This process may go through
373 several iterations. Once your patch is deemed good enough, it will be
374 committed to the official Libav tree.
375
376 Give us a few days to react. But if some time passes without reaction,
377 send a reminder by email. Your patch should eventually be dealt with.
378
379
380 @section New codecs or formats checklist
381
382 @enumerate
383 @item
384 Did you use av_cold for codec initialization and close functions?
385 @item
386 Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
387 AVInputFormat/AVOutputFormat struct?
388 @item
389 Did you bump the minor version number (and reset the micro version
390 number) in @file{libavcodec/version.h} or @file{libavformat/version.h}?
391 @item
392 Did you register it in @file{allcodecs.c} or @file{allformats.c}?
393 @item
394 Did you add the CodecID to @file{avcodec.h}?
395 @item
396 If it has a fourcc, did you add it to @file{libavformat/riff.c},
397 even if it is only a decoder?
398 @item
399 Did you add a rule to compile the appropriate files in the Makefile?
400 Remember to do this even if you are just adding a format to a file that
401 is already being compiled by some other rule, like a raw demuxer.
402 @item
403 Did you add an entry to the table of supported formats or codecs in
404 @file{doc/general.texi}?
405 @item
406 Did you add an entry in the Changelog?
407 @item
408 If it depends on a parser or a library, did you add that dependency in
409 configure?
410 @item
411 Did you @code{git add} the appropriate files before committing?
412 @item
413 Did you make sure it compiles standalone, i.e. with
414 @code{configure --disable-everything --enable-decoder=foo}
415 (or @code{--enable-demuxer} or whatever your component is)?
416 @end enumerate
417
418
419 @section patch submission checklist
420
421 @enumerate
422 @item
423 Does @code{make fate} pass with the patch applied?
424 @item
425 Does @code{make checkheaders} pass with the patch applied?
426 @item
427 Is the patch against latest Libav git master branch?
428 @item
429 Are you subscribed to the
430 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
431 mailing list? (Only list subscribers are allowed to post.)
432 @item
433 Have you checked that the changes are minimal, so that the same cannot be
434 achieved with a smaller patch and/or simpler final code?
435 @item
436 If the change is to speed critical code, did you benchmark it?
437 @item
438 If you did any benchmarks, did you provide them in the mail?
439 @item
440 Have you checked that the patch does not introduce buffer overflows or
441 other security issues?
442 @item
443 Did you test your decoder or demuxer against damaged data? If no, see
444 tools/trasher and the noise bitstream filter. Your decoder or demuxer
445 should not crash or end in a (near) infinite loop when fed damaged data.
446 @item
447 Does the patch not mix functional and cosmetic changes?
448 @item
449 Did you add tabs or trailing whitespace to the code? Both are forbidden.
450 @item
451 Is the patch attached to the email you send?
452 @item
453 Is the mime type of the patch correct? It should be text/x-diff or
454 text/x-patch or at least text/plain and not application/octet-stream.
455 @item
456 If the patch fixes a bug, did you provide a verbose analysis of the bug?
457 @item
458 If the patch fixes a bug, did you provide enough information, including
459 a sample, so the bug can be reproduced and the fix can be verified?
460 Note please do not attach samples >100k to mails but rather provide a
461 URL, you can upload to ftp://upload.libav.org
462 @item
463 Did you provide a verbose summary about what the patch does change?
464 @item
465 Did you provide a verbose explanation why it changes things like it does?
466 @item
467 Did you provide a verbose summary of the user visible advantages and
468 disadvantages if the patch is applied?
469 @item
470 Did you provide an example so we can verify the new feature added by the
471 patch easily?
472 @item
473 If you added a new file, did you insert a license header? It should be
474 taken from Libav, not randomly copied and pasted from somewhere else.
475 @item
476 You should maintain alphabetical order in alphabetically ordered lists as
477 long as doing so does not break API/ABI compatibility.
478 @item
479 Lines with similar content should be aligned vertically when doing so
480 improves readability.
481 @end enumerate
482
483 @section Patch review process
484
485 All patches posted to the
486 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
487 mailing list will be reviewed, unless they contain a
488 clear note that the patch is not for the git master branch.
489 Reviews and comments will be posted as replies to the patch on the
490 mailing list. The patch submitter then has to take care of every comment,
491 that can be by resubmitting a changed patch or by discussion. Resubmitted
492 patches will themselves be reviewed like any other patch. If at some point
493 a patch passes review with no comments then it is approved, that can for
494 simple and small patches happen immediately while large patches will generally
495 have to be changed and reviewed many times before they are approved.
496 After a patch is approved it will be committed to the repository.
497
498 We will review all submitted patches, but sometimes we are quite busy so
499 especially for large patches this can take several weeks.
500
501 When resubmitting patches, if their size grew or during the review different
502 issues arisen please split the patch so each issue has a specific patch.
503
504 @anchor{Regression Tests}
505 @section Regression Tests
506
507 Before submitting a patch (or committing to the repository), you should at
508 least make sure that it does not break anything.
509
510 If the code changed has already a test present in FATE you should run it,
511 otherwise it is advised to add it.
512
513 Improvements to codec or demuxer might change the FATE results. Make sure
514 to commit the update reference with the change and to explain in the comment
515 why the expected result changed.
516
517 Please refer to @file{doc/fate.txt}.
518
519 @bye