doc: add editor configuration section with Vim and Emacs settings
[libav.git] / doc / developer.texi
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1\input texinfo @c -*- texinfo -*-
2
3@settitle Developer Documentation
4@titlepage
a752069d 5@center @titlefont{Developer Documentation}
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6@end titlepage
7
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8@top
9
10@contents
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11
12@chapter Developers Guide
13
14@section API
15@itemize @bullet
16@item libavcodec is the library containing the codecs (both encoding and
17decoding). 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
266463da 20demux code for several formats). Look at @file{avplay.c} to use it in a
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21player. See @file{libavformat/output-example.c} to use it to generate
22audio or video streams.
23
24@end itemize
25
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26@section Integrating libav in your program
27
28Shared libraries should be used whenever is possible in order to reduce
29the effort distributors have to pour to support programs and to ensure
30only the public api is used.
31
32You can use Libav in your commercial program, but you must abide to the
33license, LGPL or GPL depending on the specific features used, please refer
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34to @uref{http://libav.org/legal.html, our legal page} for a quick checklist and to
35the 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}.
4c362a52 40Any modification to the source code can be suggested for inclusion.
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41The best way to proceed is to send your patches to the
42@uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
43mailing list.
a752069d 44
72cdcc0b 45@anchor{Coding Rules}
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46@section Coding Rules
47
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48@subsection Code formatting conventions
49The code is written in K&R C style. That means the following:
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50@itemize @bullet
51@item
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52The control statements are formatted by putting space betwen the statement
53and parenthesis in the following way:
9b9815ee 54@example
84994421 55for (i = 0; i < filter->input_count; i++) @{
9b9815ee 56@end example
a752069d 57@item
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58The case statement is always located at the same level as the switch itself:
59@example
60switch (link->init_state) @{
61case AVLINK_INIT:
62 continue;
63case AVLINK_STARTINIT:
64 av_log(filter, AV_LOG_INFO, "circular filter chain detected");
65 return 0;
66@end example
a752069d 67@item
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68Braces in function declarations are written on the new line:
69@example
70const char *avfilter_configuration(void)
71@{
72 return LIBAV_CONFIGURATION;
73@}
74@end example
a752069d 75@item
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76In case of a single-statement if, no curly braces are required:
77@example
78if (!pic || !picref)
79 goto fail;
80@end example
81@item
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82Do not put spaces immediately inside parenthesis. @samp{if (ret)} is
83a valid style; @samp{if ( ret )} is not.
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84@end itemize
85
9b9815ee 86There are the following guidelines regarding the indentation in files:
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87@itemize @bullet
88@item
a752069d 89Indent size is 4.
9b9815ee 90@item
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91The TAB character is forbidden outside of Makefiles as is any
92form of trailing whitespace. Commits containing either will be
faa6f1c3 93rejected by the git repository.
9b9815ee 94@item
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95You should try to limit your code lines to 80 characters; however, do so if
96and only if this improves readability.
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97@end itemize
98The presentation is one inspired by 'indent -i4 -kr -nut'.
a752069d 99
f8a45fa1 100The main priority in Libav is simplicity and small code size in order to
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101minimize the bug count.
102
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103@subsection Comments
104Use the JavaDoc/Doxygen format (see examples below) so that code documentation
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105can be generated automatically. All nontrivial functions should have a comment
106above them explaining what the function does, even if it is just one sentence.
107All structures and their member variables should be documented, too.
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108
109Avoid Qt-style and similar Doxygen syntax with @code{!} in it, i.e. replace
110@code{//!} with @code{///} and similar. Also @@ syntax should be employed
111for markup commands, i.e. use @code{@@param} and not @code{\param}.
112
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113@example
114/**
a2f31564 115 * @@file
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116 * MPEG codec.
117 * @@author ...
118 */
119
120/**
121 * Summary sentence.
122 * more text ...
123 * ...
124 */
125typedef 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 */
139int myfunc(int my_parameter)
140...
141@end example
142
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143@subsection C language features
144
145Libav is programmed in the ISO C90 language with a few additional
146features from ISO C99, namely:
147@itemize @bullet
148@item
149the @samp{inline} keyword;
150@item
151@samp{//} comments;
152@item
153designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
154@item
155compound literals (@samp{x = (struct s) @{ 17, 23 @};})
156@end itemize
157
158These features are supported by all compilers we care about, so we will not
159accept patches to remove their use unless they absolutely do not impair
160clarity and performance.
161
162All code must compile with recent versions of GCC and a number of other
163currently supported compilers. To ensure compatibility, please do not use
164additional C99 features or GCC extensions. Especially watch out for:
165@itemize @bullet
166@item
167mixing 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
173GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
174@end itemize
175
176@subsection Naming conventions
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177All 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
180names; they should always be in the CamelCase
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181
182There are following conventions for naming variables and functions:
183@itemize @bullet
184@item
185For local variables no prefix is required.
186@item
187For variables and functions declared as @code{static} no prefixes are required.
188@item
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189For variables and functions used internally by the library, @code{ff_} prefix
190should be used.
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191For example, @samp{ff_w64_demuxer}.
192@item
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193For variables and functions used internally across multiple libraries, use
194@code{avpriv_}. For example, @samp{avpriv_aac_parse_header}.
9b9815ee 195@item
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196For exported names, each library has its own prefixes. Just check the existing
197code and name accordingly.
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198@end itemize
199
200@subsection Miscellanous conventions
201@itemize @bullet
202@item
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203fprintf and printf are forbidden in libavformat and libavcodec,
204please use av_log() instead.
9b9815ee 205@item
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206Casts should be used only when necessary. Unneeded parentheses
207should also be avoided if they don't make the code easier to understand.
9b9815ee 208@end itemize
a752069d 209
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210@subsection Editor configuration
211In order to configure Vim to follow Libav formatting conventions, paste
212the following snippet into your @file{.vimrc}:
213@example
214" indentation rules for libav: 4 spaces, no tabs
215set expandtab
216set shiftwidth=4
217set softtabstop=4
218" allow tabs in Makefiles
219autocmd FileType make set noexpandtab shiftwidth=8 softtabstop=8
220" Trailing whitespace and tabs are forbidden, so highlight them.
221highlight ForbiddenWhitespace ctermbg=red guibg=red
222match ForbiddenWhitespace /\s\+$\|\t/
223" Do not highlight spaces at the end of line while typing on that line.
224autocmd InsertEnter * match ForbiddenWhitespace /\t\|\s\+\%#\@@<!$/
225@end example
226
227For 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
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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
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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.
a752069d 254@item
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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.
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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.
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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.
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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
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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.
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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.
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295@item
296 Update the documentation if you change behavior or add features. If you are
4c362a52 297 unsure how best to do this, send an [RFC] patch to libav-devel.
a752069d 298@item
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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.
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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
4c362a52 306 as array index or other risky things. Always use valgrind to doublecheck.
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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
4c362a52 319 Compiler warnings indicate potential bugs or code with bad style.
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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.
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323 If a type of warning leads to too many false positives, that warning
324 should be disabled, not the code changed.
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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
330We think our rules are not too hard. If you have comments, contact us.
331
4c362a52 332Note, some rules were borrowed from the MPlayer project.
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333
334@section Submitting patches
335
4c989761 336First, read the @ref{Coding Rules} above if you did not yet, in particular
4c362a52 337the rules regarding patch submission.
a752069d 338
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339As stated already, please do not submit a patch which contains several
340unrelated changes.
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341Split it into separate, self-contained pieces. This does not mean splitting
342file by file. Instead, make the patch as small as possible while still
343keeping it as a logical unit that contains an individual change, even
344if it spans multiple files. This makes reviewing your patches much easier
345for us and greatly increases your chances of getting your patch applied.
346
f8a45fa1 347Use the patcheck tool of Libav to check your patch.
65214b62 348The tool is located in the tools directory.
24b403f3 349
4c989761 350Run the @ref{Regression Tests} before submitting a patch in order to verify
4c362a52 351it does not cause unexpected problems.
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352
353Patches should be posted as base64 encoded attachments (or any other
354encoding which ensures that the patch will not be trashed during
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355transmission) to the
356@uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
357mailing list.
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358
359It 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
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361and has no lrint()'). This kind of explanation should be the body of the
362commit message.
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363
364Also please if you send several patches, send each patch as a separate mail,
365do not attach several unrelated patches to the same mail.
366
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367Use @code{git send-email} when possible since it will properly send patches
368without requiring extra care.
369
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370Your patch will be reviewed on the mailing list. You will likely be asked
371to make some changes and are expected to send in an improved version that
372incorporates the requests from the review. This process may go through
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373several iterations. Once your patch is deemed good enough, it will be
374committed to the official Libav tree.
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375
376Give us a few days to react. But if some time passes without reaction,
377send a reminder by email. Your patch should eventually be dealt with.
378
379
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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
7dbcc4f8 389 Did you bump the minor version number (and reset the micro version
dd8d808b 390 number) in @file{libavcodec/version.h} or @file{libavformat/version.h}?
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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?
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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.
a752069d 402@item
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403 Did you add an entry to the table of supported formats or codecs in
404 @file{doc/general.texi}?
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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
4c362a52 411 Did you @code{git add} the appropriate files before committing?
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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)?
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416@end enumerate
417
af1ca249 418
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419@section patch submission checklist
420
421@enumerate
422@item
2dbdb309 423 Does @code{make fate} pass with the patch applied?
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424@item
425 Does @code{make checkheaders} pass with the patch applied?
426@item
f8a45fa1 427 Is the patch against latest Libav git master branch?
a752069d 428@item
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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.)
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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
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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
21de9204 461 URL, you can upload to ftp://upload.libav.org
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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
f8a45fa1 474 taken from Libav, not randomly copied and pasted from somewhere else.
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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.
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481@end enumerate
482
483@section Patch review process
484
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485All patches posted to the
486@uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
487mailing list will be reviewed, unless they contain a
87800dc2 488clear note that the patch is not for the git master branch.
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489Reviews and comments will be posted as replies to the patch on the
490mailing list. The patch submitter then has to take care of every comment,
491that can be by resubmitting a changed patch or by discussion. Resubmitted
492patches will themselves be reviewed like any other patch. If at some point
493a patch passes review with no comments then it is approved, that can for
494simple and small patches happen immediately while large patches will generally
495have to be changed and reviewed many times before they are approved.
496After a patch is approved it will be committed to the repository.
497
498We will review all submitted patches, but sometimes we are quite busy so
499especially for large patches this can take several weeks.
500
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501When resubmitting patches, if their size grew or during the review different
502issues arisen please split the patch so each issue has a specific patch.
a752069d 503
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504@anchor{Regression Tests}
505@section Regression Tests
a752069d 506
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507Before submitting a patch (or committing to the repository), you should at
508least make sure that it does not break anything.
a752069d 509
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510If the code changed has already a test present in FATE you should run it,
511otherwise it is advised to add it.
a752069d 512
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513Improvements to codec or demuxer might change the FATE results. Make sure
514to commit the update reference with the change and to explain in the comment
515why the expected result changed.
a752069d 516
4c362a52 517Please refer to @file{doc/fate.txt}.
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518
519@bye