doc: Extend commit message section
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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
9a00374c 30only the public API is used.
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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
da9cea77 52The control statements are formatted by putting space between the statement
a0338b59 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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76Do not check for NULL values by comparison, @samp{if (p)} and
77@samp{if (!p)} are correct; @samp{if (p == NULL)} and @samp{if (p != NULL)}
78are not.
79@item
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80In case of a single-statement if, no curly braces are required:
81@example
82if (!pic || !picref)
83 goto fail;
84@end example
85@item
da9cea77 86Do not put spaces immediately inside parentheses. @samp{if (ret)} is
a0338b59 87a valid style; @samp{if ( ret )} is not.
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88@end itemize
89
9b9815ee 90There are the following guidelines regarding the indentation in files:
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91@itemize @bullet
92@item
a752069d 93Indent size is 4.
9b9815ee 94@item
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95The TAB character is forbidden outside of Makefiles as is any
96form of trailing whitespace. Commits containing either will be
faa6f1c3 97rejected by the git repository.
9b9815ee 98@item
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99You should try to limit your code lines to 80 characters; however, do so if
100and only if this improves readability.
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101@end itemize
102The presentation is one inspired by 'indent -i4 -kr -nut'.
a752069d 103
f8a45fa1 104The main priority in Libav is simplicity and small code size in order to
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105minimize the bug count.
106
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107@subsection Comments
108Use the JavaDoc/Doxygen format (see examples below) so that code documentation
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109can be generated automatically. All nontrivial functions should have a comment
110above them explaining what the function does, even if it is just one sentence.
111All structures and their member variables should be documented, too.
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112
113Avoid Qt-style and similar Doxygen syntax with @code{!} in it, i.e. replace
114@code{//!} with @code{///} and similar. Also @@ syntax should be employed
115for markup commands, i.e. use @code{@@param} and not @code{\param}.
116
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117@example
118/**
a2f31564 119 * @@file
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120 * MPEG codec.
121 * @@author ...
122 */
123
124/**
125 * Summary sentence.
126 * more text ...
127 * ...
128 */
129typedef struct Foobar@{
130 int var1; /**< var1 description */
131 int var2; ///< var2 description
132 /** var3 description */
133 int var3;
134@} Foobar;
135
136/**
137 * Summary sentence.
138 * more text ...
139 * ...
140 * @@param my_parameter description of my_parameter
141 * @@return return value description
142 */
143int myfunc(int my_parameter)
144...
145@end example
146
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147@subsection C language features
148
149Libav is programmed in the ISO C90 language with a few additional
150features from ISO C99, namely:
151@itemize @bullet
152@item
153the @samp{inline} keyword;
154@item
155@samp{//} comments;
156@item
157designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
158@item
159compound literals (@samp{x = (struct s) @{ 17, 23 @};})
160@end itemize
161
162These features are supported by all compilers we care about, so we will not
163accept patches to remove their use unless they absolutely do not impair
164clarity and performance.
165
166All code must compile with recent versions of GCC and a number of other
167currently supported compilers. To ensure compatibility, please do not use
168additional C99 features or GCC extensions. Especially watch out for:
169@itemize @bullet
170@item
171mixing statements and declarations;
172@item
173@samp{long long} (use @samp{int64_t} instead);
174@item
175@samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;
176@item
177GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
178@end itemize
179
180@subsection Naming conventions
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181All names are using underscores (_), not CamelCase. For example,
182@samp{avfilter_get_video_buffer} is a valid function name and
183@samp{AVFilterGetVideo} is not. The only exception from this are structure
184names; they should always be in the CamelCase
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185
186There are following conventions for naming variables and functions:
187@itemize @bullet
188@item
189For local variables no prefix is required.
190@item
191For variables and functions declared as @code{static} no prefixes are required.
192@item
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193For variables and functions used internally by the library, @code{ff_} prefix
194should be used.
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195For example, @samp{ff_w64_demuxer}.
196@item
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197For variables and functions used internally across multiple libraries, use
198@code{avpriv_}. For example, @samp{avpriv_aac_parse_header}.
9b9815ee 199@item
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200For exported names, each library has its own prefixes. Just check the existing
201code and name accordingly.
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202@end itemize
203
511cf612 204@subsection Miscellaneous conventions
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205@itemize @bullet
206@item
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207fprintf and printf are forbidden in libavformat and libavcodec,
208please use av_log() instead.
9b9815ee 209@item
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210Casts should be used only when necessary. Unneeded parentheses
211should also be avoided if they don't make the code easier to understand.
9b9815ee 212@end itemize
a752069d 213
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214@subsection Editor configuration
215In order to configure Vim to follow Libav formatting conventions, paste
216the following snippet into your @file{.vimrc}:
217@example
9a00374c 218" Indentation rules for Libav: 4 spaces, no tabs.
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219set expandtab
220set shiftwidth=4
221set softtabstop=4
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222set cindent
223set cinoptions=(0
9a00374c 224" Allow tabs in Makefiles.
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225autocmd FileType make set noexpandtab shiftwidth=8 softtabstop=8
226" Trailing whitespace and tabs are forbidden, so highlight them.
227highlight ForbiddenWhitespace ctermbg=red guibg=red
228match ForbiddenWhitespace /\s\+$\|\t/
229" Do not highlight spaces at the end of line while typing on that line.
230autocmd InsertEnter * match ForbiddenWhitespace /\t\|\s\+\%#\@@<!$/
231@end example
232
233For Emacs, add these roughly equivalent lines to your @file{.emacs.d/init.el}:
234@example
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235(c-add-style "libav"
236 '("k&r"
237 (c-basic-offset . 4)
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238 (indent-tabs-mode . nil)
239 (show-trailing-whitespace . t)
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240 (c-offsets-alist
241 (statement-cont . (c-lineup-assignments +)))
242 )
243 )
244(setq c-default-style "libav")
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245@end example
246
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247@section Development Policy
248
249@enumerate
250@item
251 Contributions should be licensed under the LGPL 2.1, including an
252 "or any later version" clause, or the MIT license. GPL 2 including
253 an "or any later version" clause is also acceptable, but LGPL is
254 preferred.
255@item
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256 All the patches MUST be reviewed in the mailing list before they are
257 committed.
258@item
259 The Libav coding style should remain consistent. Changes to
260 conform will be suggested during the review or implemented on commit.
261@item
262 Patches should be generated using @code{git format-patch} or directly sent
263 using @code{git send-email}.
264 Please make sure you give the proper credit by setting the correct author
265 in the commit.
a752069d 266@item
4c362a52 267 The commit message should have a short first line in the form of
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268 a @samp{topic: short description} as a header, separated by a newline
269 from the body consisting of an explanation of why the change is necessary.
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270 If the commit fixes a known bug on the bug tracker, the commit message
271 should include its bug ID. Referring to the issue on the bug tracker does
272 not exempt you from writing an excerpt of the bug in the commit message.
273 If the patch is a bug fix which should be backported to stable releases,
274 i.e. a non-API/ABI-breaking bug fix, add @code{CC: libav-stable@@libav.org}
275 to the bottom of your commit message, and make sure to CC your patch to
276 this address, too. Some git setups will do this automatically.
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277@item
278 Work in progress patches should be sent to the mailing list with the [WIP]
279 or the [RFC] tag.
280@item
281 Branches in public personal repos are advised as way to
282 work on issues collaboratively.
283@item
284 You do not have to over-test things. If it works for you and you think it
285 should work for others, send it to the mailing list for review.
286 If you have doubt about portability please state it in the submission so
287 people with specific hardware could test it.
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288@item
289 Do not commit unrelated changes together, split them into self-contained
290 pieces. Also do not forget that if part B depends on part A, but A does not
291 depend on B, then A can and should be committed first and separate from B.
292 Keeping changes well split into self-contained parts makes reviewing and
293 understanding them on the commit log mailing list easier. This also helps
294 in case of debugging later on.
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295@item
296 Patches that change behavior of the programs (renaming options etc) or
297 public API or ABI should be discussed in depth and possible few days should
298 pass between discussion and commit.
299 Changes to the build system (Makefiles, configure script) which alter
300 the expected behavior should be considered in the same regard.
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301@item
302 When applying patches that have been discussed (at length) on the mailing
303 list, reference the thread in the log message.
304@item
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305 Subscribe to the
306 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel} and
307 @uref{https://lists.libav.org/mailman/listinfo/libav-commits, libav-commits}
308 mailing lists.
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309 Bugs and possible improvements or general questions regarding commits
310 are discussed on libav-devel. We expect you to react if problems with
311 your code are uncovered.
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312@item
313 Update the documentation if you change behavior or add features. If you are
4c362a52 314 unsure how best to do this, send an [RFC] patch to libav-devel.
a752069d 315@item
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316 All discussions and decisions should be reported on the public developer
317 mailing list, so that there is a reference to them.
318 Other media (e.g. IRC) should be used for coordination and immediate
319 collaboration.
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320@item
321 Never write to unallocated memory, never write over the end of arrays,
322 always check values read from some untrusted source before using them
9a00374c 323 as array index or other risky things. Always use valgrind to double-check.
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324@item
325 Remember to check if you need to bump versions for the specific libav
326 parts (libavutil, libavcodec, libavformat) you are changing. You need
327 to change the version integer.
328 Incrementing the first component means no backward compatibility to
329 previous versions (e.g. removal of a function from the public API).
330 Incrementing the second component means backward compatible change
331 (e.g. addition of a function to the public API or extension of an
332 existing data structure).
333 Incrementing the third component means a noteworthy binary compatible
334 change (e.g. encoder bug fix that matters for the decoder).
335@item
4c362a52 336 Compiler warnings indicate potential bugs or code with bad style.
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337 If it is a bug, the bug has to be fixed. If it is not, the code should
338 be changed to not generate a warning unless that causes a slowdown
339 or obfuscates the code.
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340 If a type of warning leads to too many false positives, that warning
341 should be disabled, not the code changed.
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342@item
343 If you add a new file, give it a proper license header. Do not copy and
344 paste it from a random place, use an existing file as template.
345@end enumerate
346
347We think our rules are not too hard. If you have comments, contact us.
348
4c362a52 349Note, some rules were borrowed from the MPlayer project.
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350
351@section Submitting patches
352
4c989761 353First, read the @ref{Coding Rules} above if you did not yet, in particular
4c362a52 354the rules regarding patch submission.
a752069d 355
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356As stated already, please do not submit a patch which contains several
357unrelated changes.
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358Split it into separate, self-contained pieces. This does not mean splitting
359file by file. Instead, make the patch as small as possible while still
360keeping it as a logical unit that contains an individual change, even
361if it spans multiple files. This makes reviewing your patches much easier
362for us and greatly increases your chances of getting your patch applied.
363
f8a45fa1 364Use the patcheck tool of Libav to check your patch.
65214b62 365The tool is located in the tools directory.
24b403f3 366
4c989761 367Run the @ref{Regression Tests} before submitting a patch in order to verify
4c362a52 368it does not cause unexpected problems.
a752069d 369
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370It also helps quite a bit if you tell us what the patch does (for example
371'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
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372and has no lrint()'). This kind of explanation should be the body of the
373commit message.
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374
375Also please if you send several patches, send each patch as a separate mail,
376do not attach several unrelated patches to the same mail.
377
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378Patches should be posted to the
379@uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
380mailing list. Use @code{git send-email} when possible since it will properly
381send patches without requiring extra care. If you cannot, then send patches
382as base64-encoded attachments, so your patch is not trashed during
383transmission.
4c362a52 384
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385Your patch will be reviewed on the mailing list. You will likely be asked
386to make some changes and are expected to send in an improved version that
387incorporates the requests from the review. This process may go through
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388several iterations. Once your patch is deemed good enough, it will be
389committed to the official Libav tree.
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390
391Give us a few days to react. But if some time passes without reaction,
392send a reminder by email. Your patch should eventually be dealt with.
393
394
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395@section New codecs or formats checklist
396
397@enumerate
398@item
399 Did you use av_cold for codec initialization and close functions?
400@item
401 Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
402 AVInputFormat/AVOutputFormat struct?
403@item
7dbcc4f8 404 Did you bump the minor version number (and reset the micro version
dd8d808b 405 number) in @file{libavcodec/version.h} or @file{libavformat/version.h}?
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406@item
407 Did you register it in @file{allcodecs.c} or @file{allformats.c}?
408@item
36ef5369 409 Did you add the AVCodecID to @file{avcodec.h}?
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410 When adding new codec IDs, also add an entry to the codec descriptor
411 list in @file{libavcodec/codec_desc.c}.
a752069d 412@item
9a00374c 413 If it has a FourCC, did you add it to @file{libavformat/riff.c},
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414 even if it is only a decoder?
415@item
416 Did you add a rule to compile the appropriate files in the Makefile?
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417 Remember to do this even if you are just adding a format to a file that
418 is already being compiled by some other rule, like a raw demuxer.
a752069d 419@item
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420 Did you add an entry to the table of supported formats or codecs in
421 @file{doc/general.texi}?
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422@item
423 Did you add an entry in the Changelog?
424@item
425 If it depends on a parser or a library, did you add that dependency in
426 configure?
427@item
4c362a52 428 Did you @code{git add} the appropriate files before committing?
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429@item
430 Did you make sure it compiles standalone, i.e. with
431 @code{configure --disable-everything --enable-decoder=foo}
432 (or @code{--enable-demuxer} or whatever your component is)?
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433@end enumerate
434
af1ca249 435
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436@section patch submission checklist
437
438@enumerate
439@item
4982e1dd 440 Does @code{make check} pass with the patch applied?
a752069d 441@item
f8a45fa1 442 Is the patch against latest Libav git master branch?
a752069d 443@item
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444 Are you subscribed to the
445 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
446 mailing list? (Only list subscribers are allowed to post.)
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447@item
448 Have you checked that the changes are minimal, so that the same cannot be
449 achieved with a smaller patch and/or simpler final code?
450@item
451 If the change is to speed critical code, did you benchmark it?
452@item
453 If you did any benchmarks, did you provide them in the mail?
454@item
455 Have you checked that the patch does not introduce buffer overflows or
456 other security issues?
457@item
458 Did you test your decoder or demuxer against damaged data? If no, see
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459 tools/trasher, the noise bitstream filter, and
460 @uref{http://caca.zoy.org/wiki/zzuf, zzuf}. Your decoder or demuxer
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461 should not crash, end in a (near) infinite loop, or allocate ridiculous
462 amounts of memory when fed damaged data.
a752069d 463@item
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464 Does the patch not mix functional and cosmetic changes?
465@item
466 Did you add tabs or trailing whitespace to the code? Both are forbidden.
467@item
468 Is the patch attached to the email you send?
469@item
470 Is the mime type of the patch correct? It should be text/x-diff or
471 text/x-patch or at least text/plain and not application/octet-stream.
472@item
473 If the patch fixes a bug, did you provide a verbose analysis of the bug?
474@item
475 If the patch fixes a bug, did you provide enough information, including
476 a sample, so the bug can be reproduced and the fix can be verified?
477 Note please do not attach samples >100k to mails but rather provide a
21de9204 478 URL, you can upload to ftp://upload.libav.org
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479@item
480 Did you provide a verbose summary about what the patch does change?
481@item
482 Did you provide a verbose explanation why it changes things like it does?
483@item
484 Did you provide a verbose summary of the user visible advantages and
485 disadvantages if the patch is applied?
486@item
487 Did you provide an example so we can verify the new feature added by the
488 patch easily?
489@item
490 If you added a new file, did you insert a license header? It should be
f8a45fa1 491 taken from Libav, not randomly copied and pasted from somewhere else.
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492@item
493 You should maintain alphabetical order in alphabetically ordered lists as
494 long as doing so does not break API/ABI compatibility.
495@item
496 Lines with similar content should be aligned vertically when doing so
497 improves readability.
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498@item
499 Make sure you check the return values of function and return appropriate
500 error codes. Especially memory allocation functions like @code{malloc()}
501 are notoriously left unchecked, which is a serious problem.
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502@end enumerate
503
504@section Patch review process
505
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506All patches posted to the
507@uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
508mailing list will be reviewed, unless they contain a
87800dc2 509clear note that the patch is not for the git master branch.
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510Reviews and comments will be posted as replies to the patch on the
511mailing list. The patch submitter then has to take care of every comment,
512that can be by resubmitting a changed patch or by discussion. Resubmitted
513patches will themselves be reviewed like any other patch. If at some point
514a patch passes review with no comments then it is approved, that can for
515simple and small patches happen immediately while large patches will generally
516have to be changed and reviewed many times before they are approved.
517After a patch is approved it will be committed to the repository.
518
519We will review all submitted patches, but sometimes we are quite busy so
520especially for large patches this can take several weeks.
521
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522When resubmitting patches, if their size grew or during the review different
523issues arisen please split the patch so each issue has a specific patch.
a752069d 524
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525@anchor{Regression Tests}
526@section Regression Tests
a752069d 527
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528Before submitting a patch (or committing to the repository), you should at
529least make sure that it does not break anything.
a752069d 530
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531If the code changed has already a test present in FATE you should run it,
532otherwise it is advised to add it.
a752069d 533
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534Improvements to codec or demuxer might change the FATE results. Make sure
535to commit the update reference with the change and to explain in the comment
536why the expected result changed.
a752069d 537
86ae5124 538Please refer to @url{fate.html}.
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539
540@bye