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 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 20demux code for several formats). Look at @file{avplay.c} to use it in a 21player. See @file{libavformat/output-example.c} to use it to generate 22audio or video streams. 23 24@end itemize 25 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 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}. 40Any modification to the source code can be suggested for inclusion. 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. 44 45@anchor{Coding Rules} 46@section Coding Rules 47 48@subsection Code formatting conventions 49The code is written in K&R C style. That means the following: 50@itemize @bullet 51@item 52The control statements are formatted by putting space between the statement 53and parenthesis in the following way: 54@example 55for (i = 0; i < filter->input_count; i++) @{ 56@end example 57@item 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 67@item 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 75@item 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 82Do not put spaces immediately inside parentheses. @samp{if (ret)} is 83a valid style; @samp{if ( ret )} is not. 84@end itemize 85 86There are the following guidelines regarding the indentation in files: 87@itemize @bullet 88@item 89Indent size is 4. 90@item 91The TAB character is forbidden outside of Makefiles as is any 92form of trailing whitespace. Commits containing either will be 93rejected by the git repository. 94@item 95You should try to limit your code lines to 80 characters; however, do so if 96and only if this improves readability. 97@end itemize 98The presentation is one inspired by 'indent -i4 -kr -nut'. 99 100The main priority in Libav is simplicity and small code size in order to 101minimize the bug count. 102 103@subsection Comments 104Use the JavaDoc/Doxygen format (see examples below) so that code documentation 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. 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}. 112 113@example 114/** 115 * @@file 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 142 143@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 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 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 189For variables and functions used internally by the library, @code{ff_} prefix 190should be used. 191For example, @samp{ff_w64_demuxer}. 192@item 193For variables and functions used internally across multiple libraries, use 194@code{avpriv_}. For example, @samp{avpriv_aac_parse_header}. 195@item 196For exported names, each library has its own prefixes. Just check the existing 197code and name accordingly. 198@end itemize 199 200@subsection Miscellanous conventions 201@itemize @bullet 202@item 203fprintf and printf are forbidden in libavformat and libavcodec, 204please use av_log() instead. 205@item 206Casts should be used only when necessary. Unneeded parentheses 207should also be avoided if they don't make the code easier to understand. 208@end itemize 209 210@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,automake 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 234 235@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 330We think our rules are not too hard. If you have comments, contact us. 331 332Note, some rules were borrowed from the MPlayer project. 333 334@section Submitting patches 335 336First, read the @ref{Coding Rules} above if you did not yet, in particular 337the rules regarding patch submission. 338 339As stated already, please do not submit a patch which contains several 340unrelated changes. 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 347Use the patcheck tool of Libav to check your patch. 348The tool is located in the tools directory. 349 350Run the @ref{Regression Tests} before submitting a patch in order to verify 351it does not cause unexpected problems. 352 353Patches should be posted as base64 encoded attachments (or any other 354encoding which ensures that the patch will not be trashed during 355transmission) to the 356@uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel} 357mailing list. 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 361and has no lrint()'). This kind of explanation should be the body of the 362commit message. 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 367Use @code{git send-email} when possible since it will properly send patches 368without requiring extra care. 369 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 373several iterations. Once your patch is deemed good enough, it will be 374committed to the official Libav tree. 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. 378 379 380@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 check} pass with the patch applied? 424@item 425 Is the patch against latest Libav git master branch? 426@item 427 Are you subscribed to the 428 @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel} 429 mailing list? (Only list subscribers are allowed to post.) 430@item 431 Have you checked that the changes are minimal, so that the same cannot be 432 achieved with a smaller patch and/or simpler final code? 433@item 434 If the change is to speed critical code, did you benchmark it? 435@item 436 If you did any benchmarks, did you provide them in the mail? 437@item 438 Have you checked that the patch does not introduce buffer overflows or 439 other security issues? 440@item 441 Did you test your decoder or demuxer against damaged data? If no, see 442 tools/trasher and the noise bitstream filter. Your decoder or demuxer 443 should not crash or end in a (near) infinite loop when fed damaged data. 444@item 445 Does the patch not mix functional and cosmetic changes? 446@item 447 Did you add tabs or trailing whitespace to the code? Both are forbidden. 448@item 449 Is the patch attached to the email you send? 450@item 451 Is the mime type of the patch correct? It should be text/x-diff or 452 text/x-patch or at least text/plain and not application/octet-stream. 453@item 454 If the patch fixes a bug, did you provide a verbose analysis of the bug? 455@item 456 If the patch fixes a bug, did you provide enough information, including 457 a sample, so the bug can be reproduced and the fix can be verified? 458 Note please do not attach samples >100k to mails but rather provide a 459 URL, you can upload to ftp://upload.libav.org 460@item 461 Did you provide a verbose summary about what the patch does change? 462@item 463 Did you provide a verbose explanation why it changes things like it does? 464@item 465 Did you provide a verbose summary of the user visible advantages and 466 disadvantages if the patch is applied? 467@item 468 Did you provide an example so we can verify the new feature added by the 469 patch easily? 470@item 471 If you added a new file, did you insert a license header? It should be 472 taken from Libav, not randomly copied and pasted from somewhere else. 473@item 474 You should maintain alphabetical order in alphabetically ordered lists as 475 long as doing so does not break API/ABI compatibility. 476@item 477 Lines with similar content should be aligned vertically when doing so 478 improves readability. 479@end enumerate 480 481@section Patch review process 482 483All patches posted to the 484@uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel} 485mailing list will be reviewed, unless they contain a 486clear note that the patch is not for the git master branch. 487Reviews and comments will be posted as replies to the patch on the 488mailing list. The patch submitter then has to take care of every comment, 489that can be by resubmitting a changed patch or by discussion. Resubmitted 490patches will themselves be reviewed like any other patch. If at some point 491a patch passes review with no comments then it is approved, that can for 492simple and small patches happen immediately while large patches will generally 493have to be changed and reviewed many times before they are approved. 494After a patch is approved it will be committed to the repository. 495 496We will review all submitted patches, but sometimes we are quite busy so 497especially for large patches this can take several weeks. 498 499When resubmitting patches, if their size grew or during the review different 500issues arisen please split the patch so each issue has a specific patch. 501 502@anchor{Regression Tests} 503@section Regression Tests 504 505Before submitting a patch (or committing to the repository), you should at 506least make sure that it does not break anything. 507 508If the code changed has already a test present in FATE you should run it, 509otherwise it is advised to add it. 510 511Improvements to codec or demuxer might change the FATE results. Make sure 512to commit the update reference with the change and to explain in the comment 513why the expected result changed. 514 515Please refer to @url{fate.html}. 516 517@bye 518