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  1. \input texinfo @c -*- texinfo -*-
  2. @settitle Developer Documentation
  3. @titlepage
  4. @center @titlefont{Developer Documentation}
  5. @end titlepage
  6. @top
  7. @contents
  8. @chapter Developers Guide
  9. @section API
  10. @itemize @bullet
  11. @item libavcodec is the library containing the codecs (both encoding and
  12. decoding). Look at @file{libavcodec/apiexample.c} to see how to use it.
  13. @item libavformat is the library containing the file format handling (mux and
  14. demux code for several formats). Look at @file{ffplay.c} to use it in a
  15. player. See @file{libavformat/output-example.c} to use it to generate
  16. audio or video streams.
  17. @end itemize
  18. @section Integrating libavcodec or libavformat in your program
  19. You can integrate all the source code of the libraries to link them
  20. statically to avoid any version problem. All you need is to provide a
  21. 'config.mak' and a 'config.h' in the parent directory. See the defines
  22. generated by ./configure to understand what is needed.
  23. You can use libavcodec or libavformat in your commercial program, but
  24. @emph{any patch you make must be published}. The best way to proceed is
  25. to send your patches to the FFmpeg mailing list.
  26. @section Contributing
  27. There are 3 ways by which code gets into ffmpeg.
  28. @itemize @bullet
  29. @item Submitting Patches to the main developer mailing list
  30. see @ref{Submitting patches} for details.
  31. @item Directly committing changes to the main tree.
  32. @item Committing changes to a git clone, for example on github.com or
  33. gitorious.org. And asking us to merge these changes.
  34. @end itemize
  35. Whichever way, changes should be reviewed by the maintainer of the code
  36. before they are committed. And they should follow the @ref{Coding Rules}.
  37. The developer making the commit and the author are responsible for their changes
  38. and should try to fix issues their commit causes.
  39. @anchor{Coding Rules}
  40. @section Coding Rules
  41. @subsection Code formatting conventions
  42. There are the following guidelines regarding the indentation in files:
  43. @itemize @bullet
  44. @item
  45. Indent size is 4.
  46. @item
  47. The TAB character is forbidden outside of Makefiles as is any
  48. form of trailing whitespace. Commits containing either will be
  49. rejected by the git repository.
  50. @item
  51. You should try to limit your code lines to 80 characters; however, do so if
  52. and only if this improves readability.
  53. @end itemize
  54. The presentation is one inspired by 'indent -i4 -kr -nut'.
  55. The main priority in FFmpeg is simplicity and small code size in order to
  56. minimize the bug count.
  57. @subsection Comments
  58. Use the JavaDoc/Doxygen format (see examples below) so that code documentation
  59. can be generated automatically. All nontrivial functions should have a comment
  60. above them explaining what the function does, even if it is just one sentence.
  61. All structures and their member variables should be documented, too.
  62. Avoid Qt-style and similar Doxygen syntax with @code{!} in it, i.e. replace
  63. @code{//!} with @code{///} and similar. Also @@ syntax should be employed
  64. for markup commands, i.e. use @code{@@param} and not @code{\param}.
  65. @example
  66. /**
  67. * @@file
  68. * MPEG codec.
  69. * @@author ...
  70. */
  71. /**
  72. * Summary sentence.
  73. * more text ...
  74. * ...
  75. */
  76. typedef struct Foobar@{
  77. int var1; /**< var1 description */
  78. int var2; ///< var2 description
  79. /** var3 description */
  80. int var3;
  81. @} Foobar;
  82. /**
  83. * Summary sentence.
  84. * more text ...
  85. * ...
  86. * @@param my_parameter description of my_parameter
  87. * @@return return value description
  88. */
  89. int myfunc(int my_parameter)
  90. ...
  91. @end example
  92. @subsection C language features
  93. FFmpeg is programmed in the ISO C90 language with a few additional
  94. features from ISO C99, namely:
  95. @itemize @bullet
  96. @item
  97. the @samp{inline} keyword;
  98. @item
  99. @samp{//} comments;
  100. @item
  101. designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
  102. @item
  103. compound literals (@samp{x = (struct s) @{ 17, 23 @};})
  104. @end itemize
  105. These features are supported by all compilers we care about, so we will not
  106. accept patches to remove their use unless they absolutely do not impair
  107. clarity and performance.
  108. All code must compile with recent versions of GCC and a number of other
  109. currently supported compilers. To ensure compatibility, please do not use
  110. additional C99 features or GCC extensions. Especially watch out for:
  111. @itemize @bullet
  112. @item
  113. mixing statements and declarations;
  114. @item
  115. @samp{long long} (use @samp{int64_t} instead);
  116. @item
  117. @samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;
  118. @item
  119. GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
  120. @end itemize
  121. @subsection Naming conventions
  122. All names are using underscores (_), not CamelCase. For example, @samp{avfilter_get_video_buffer} is
  123. a valid function name and @samp{AVFilterGetVideo} is not. The exception from this are type names, like
  124. for example structs and enums; they should always be in the CamelCase
  125. There are following conventions for naming variables and functions:
  126. @itemize @bullet
  127. @item
  128. For local variables no prefix is required.
  129. @item
  130. For variables and functions declared as @code{static} no prefixes are required.
  131. @item
  132. For variables and functions used internally by the library, @code{ff_} prefix
  133. should be used.
  134. For example, @samp{ff_w64_demuxer}.
  135. @item
  136. For variables and functions used internally across multiple libraries, use
  137. @code{avpriv_}. For example, @samp{avpriv_aac_parse_header}.
  138. @item
  139. For exported names, each library has its own prefixes. Just check the existing
  140. code and name accordingly.
  141. @end itemize
  142. @subsection Miscellanous conventions
  143. @itemize @bullet
  144. @item
  145. fprintf and printf are forbidden in libavformat and libavcodec,
  146. please use av_log() instead.
  147. @item
  148. Casts should be used only when necessary. Unneeded parentheses
  149. should also be avoided if they don't make the code easier to understand.
  150. @end itemize
  151. @section Development Policy
  152. @enumerate
  153. @item
  154. Contributions should be licensed under the LGPL 2.1, including an
  155. "or any later version" clause, or the MIT license. GPL 2 including
  156. an "or any later version" clause is also acceptable, but LGPL is
  157. preferred.
  158. @item
  159. You must not commit code which breaks FFmpeg! (Meaning unfinished but
  160. enabled code which breaks compilation or compiles but does not work or
  161. breaks the regression tests)
  162. You can commit unfinished stuff (for testing etc), but it must be disabled
  163. (#ifdef etc) by default so it does not interfere with other developers'
  164. work.
  165. @item
  166. You do not have to over-test things. If it works for you, and you think it
  167. should work for others, then commit. If your code has problems
  168. (portability, triggers compiler bugs, unusual environment etc) they will be
  169. reported and eventually fixed.
  170. @item
  171. Do not commit unrelated changes together, split them into self-contained
  172. pieces. Also do not forget that if part B depends on part A, but A does not
  173. depend on B, then A can and should be committed first and separate from B.
  174. Keeping changes well split into self-contained parts makes reviewing and
  175. understanding them on the commit log mailing list easier. This also helps
  176. in case of debugging later on.
  177. Also if you have doubts about splitting or not splitting, do not hesitate to
  178. ask/discuss it on the developer mailing list.
  179. @item
  180. Do not change behavior of the programs (renaming options etc) or public
  181. API or ABI without first discussing it on the ffmpeg-devel mailing list.
  182. Do not remove functionality from the code. Just improve!
  183. Note: Redundant code can be removed.
  184. @item
  185. Do not commit changes to the build system (Makefiles, configure script)
  186. which change behavior, defaults etc, without asking first. The same
  187. applies to compiler warning fixes, trivial looking fixes and to code
  188. maintained by other developers. We usually have a reason for doing things
  189. the way we do. Send your changes as patches to the ffmpeg-devel mailing
  190. list, and if the code maintainers say OK, you may commit. This does not
  191. apply to files you wrote and/or maintain.
  192. @item
  193. We refuse source indentation and other cosmetic changes if they are mixed
  194. with functional changes, such commits will be rejected and removed. Every
  195. developer has his own indentation style, you should not change it. Of course
  196. if you (re)write something, you can use your own style, even though we would
  197. prefer if the indentation throughout FFmpeg was consistent (Many projects
  198. force a given indentation style - we do not.). If you really need to make
  199. indentation changes (try to avoid this), separate them strictly from real
  200. changes.
  201. NOTE: If you had to put if()@{ .. @} over a large (> 5 lines) chunk of code,
  202. then either do NOT change the indentation of the inner part within (do not
  203. move it to the right)! or do so in a separate commit
  204. @item
  205. Always fill out the commit log message. Describe in a few lines what you
  206. changed and why. You can refer to mailing list postings if you fix a
  207. particular bug. Comments such as "fixed!" or "Changed it." are unacceptable.
  208. Recommended format:
  209. area changed: Short 1 line description
  210. details describing what and why and giving references.
  211. @item
  212. Make sure the author of the commit is set correctly. (see git commit --author)
  213. If you apply a patch, send an
  214. answer to ffmpeg-devel (or wherever you got the patch from) saying that
  215. you applied the patch.
  216. @item
  217. When applying patches that have been discussed (at length) on the mailing
  218. list, reference the thread in the log message.
  219. @item
  220. Do NOT commit to code actively maintained by others without permission.
  221. Send a patch to ffmpeg-devel instead. If no one answers within a reasonable
  222. timeframe (12h for build failures and security fixes, 3 days small changes,
  223. 1 week for big patches) then commit your patch if you think it is OK.
  224. Also note, the maintainer can simply ask for more time to review!
  225. @item
  226. Subscribe to the ffmpeg-cvslog mailing list. The diffs of all commits
  227. are sent there and reviewed by all the other developers. Bugs and possible
  228. improvements or general questions regarding commits are discussed there. We
  229. expect you to react if problems with your code are uncovered.
  230. @item
  231. Update the documentation if you change behavior or add features. If you are
  232. unsure how best to do this, send a patch to ffmpeg-devel, the documentation
  233. maintainer(s) will review and commit your stuff.
  234. @item
  235. Try to keep important discussions and requests (also) on the public
  236. developer mailing list, so that all developers can benefit from them.
  237. @item
  238. Never write to unallocated memory, never write over the end of arrays,
  239. always check values read from some untrusted source before using them
  240. as array index or other risky things.
  241. @item
  242. Remember to check if you need to bump versions for the specific libav
  243. parts (libavutil, libavcodec, libavformat) you are changing. You need
  244. to change the version integer.
  245. Incrementing the first component means no backward compatibility to
  246. previous versions (e.g. removal of a function from the public API).
  247. Incrementing the second component means backward compatible change
  248. (e.g. addition of a function to the public API or extension of an
  249. existing data structure).
  250. Incrementing the third component means a noteworthy binary compatible
  251. change (e.g. encoder bug fix that matters for the decoder).
  252. @item
  253. Compiler warnings indicate potential bugs or code with bad style. If a type of
  254. warning always points to correct and clean code, that warning should
  255. be disabled, not the code changed.
  256. Thus the remaining warnings can either be bugs or correct code.
  257. If it is a bug, the bug has to be fixed. If it is not, the code should
  258. be changed to not generate a warning unless that causes a slowdown
  259. or obfuscates the code.
  260. @item
  261. If you add a new file, give it a proper license header. Do not copy and
  262. paste it from a random place, use an existing file as template.
  263. @end enumerate
  264. We think our rules are not too hard. If you have comments, contact us.
  265. Note, these rules are mostly borrowed from the MPlayer project.
  266. @anchor{Submitting patches}
  267. @section Submitting patches
  268. First, read the @ref{Coding Rules} above if you did not yet, in particular
  269. the rules regarding patch submission.
  270. When you submit your patch, please use @code{git format-patch} or
  271. @code{git send-email}. We cannot read other diffs :-)
  272. Also please do not submit a patch which contains several unrelated changes.
  273. Split it into separate, self-contained pieces. This does not mean splitting
  274. file by file. Instead, make the patch as small as possible while still
  275. keeping it as a logical unit that contains an individual change, even
  276. if it spans multiple files. This makes reviewing your patches much easier
  277. for us and greatly increases your chances of getting your patch applied.
  278. Use the patcheck tool of FFmpeg to check your patch.
  279. The tool is located in the tools directory.
  280. Run the @ref{Regression Tests} before submitting a patch in order to verify
  281. it does not cause unexpected problems.
  282. Patches should be posted as base64 encoded attachments (or any other
  283. encoding which ensures that the patch will not be trashed during
  284. transmission) to the ffmpeg-devel mailing list, see
  285. @url{http://lists.ffmpeg.org/mailman/listinfo/ffmpeg-devel}
  286. It also helps quite a bit if you tell us what the patch does (for example
  287. 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
  288. and has no lrint()')
  289. Also please if you send several patches, send each patch as a separate mail,
  290. do not attach several unrelated patches to the same mail.
  291. Your patch will be reviewed on the mailing list. You will likely be asked
  292. to make some changes and are expected to send in an improved version that
  293. incorporates the requests from the review. This process may go through
  294. several iterations. Once your patch is deemed good enough, some developer
  295. will pick it up and commit it to the official FFmpeg tree.
  296. Give us a few days to react. But if some time passes without reaction,
  297. send a reminder by email. Your patch should eventually be dealt with.
  298. @section New codecs or formats checklist
  299. @enumerate
  300. @item
  301. Did you use av_cold for codec initialization and close functions?
  302. @item
  303. Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
  304. AVInputFormat/AVOutputFormat struct?
  305. @item
  306. Did you bump the minor version number (and reset the micro version
  307. number) in @file{libavcodec/version.h} or @file{libavformat/version.h}?
  308. @item
  309. Did you register it in @file{allcodecs.c} or @file{allformats.c}?
  310. @item
  311. Did you add the CodecID to @file{avcodec.h}?
  312. @item
  313. If it has a fourCC, did you add it to @file{libavformat/riff.c},
  314. even if it is only a decoder?
  315. @item
  316. Did you add a rule to compile the appropriate files in the Makefile?
  317. Remember to do this even if you're just adding a format to a file that is
  318. already being compiled by some other rule, like a raw demuxer.
  319. @item
  320. Did you add an entry to the table of supported formats or codecs in
  321. @file{doc/general.texi}?
  322. @item
  323. Did you add an entry in the Changelog?
  324. @item
  325. If it depends on a parser or a library, did you add that dependency in
  326. configure?
  327. @item
  328. Did you @code{git add} the appropriate files before committing?
  329. @item
  330. Did you make sure it compiles standalone, i.e. with
  331. @code{configure --disable-everything --enable-decoder=foo}
  332. (or @code{--enable-demuxer} or whatever your component is)?
  333. @end enumerate
  334. @section patch submission checklist
  335. @enumerate
  336. @item
  337. Does @code{make fate} pass with the patch applied?
  338. @item
  339. Was the patch generated with git format-patch or send-email?
  340. @item
  341. Did you sign off your patch? (git commit -s)
  342. See @url{http://kerneltrap.org/files/Jeremy/DCO.txt} for the meaning
  343. of sign off.
  344. @item
  345. Did you provide a clear git commit log message?
  346. @item
  347. Is the patch against latest FFmpeg git master branch?
  348. @item
  349. Are you subscribed to ffmpeg-devel?
  350. (the list is subscribers only due to spam)
  351. @item
  352. Have you checked that the changes are minimal, so that the same cannot be
  353. achieved with a smaller patch and/or simpler final code?
  354. @item
  355. If the change is to speed critical code, did you benchmark it?
  356. @item
  357. If you did any benchmarks, did you provide them in the mail?
  358. @item
  359. Have you checked that the patch does not introduce buffer overflows or
  360. other security issues?
  361. @item
  362. Did you test your decoder or demuxer against damaged data? If no, see
  363. tools/trasher and the noise bitstream filter. Your decoder or demuxer
  364. should not crash or end in a (near) infinite loop when fed damaged data.
  365. @item
  366. Does the patch not mix functional and cosmetic changes?
  367. @item
  368. Did you add tabs or trailing whitespace to the code? Both are forbidden.
  369. @item
  370. Is the patch attached to the email you send?
  371. @item
  372. Is the mime type of the patch correct? It should be text/x-diff or
  373. text/x-patch or at least text/plain and not application/octet-stream.
  374. @item
  375. If the patch fixes a bug, did you provide a verbose analysis of the bug?
  376. @item
  377. If the patch fixes a bug, did you provide enough information, including
  378. a sample, so the bug can be reproduced and the fix can be verified?
  379. Note please do not attach samples >100k to mails but rather provide a
  380. URL, you can upload to ftp://upload.ffmpeg.org
  381. @item
  382. Did you provide a verbose summary about what the patch does change?
  383. @item
  384. Did you provide a verbose explanation why it changes things like it does?
  385. @item
  386. Did you provide a verbose summary of the user visible advantages and
  387. disadvantages if the patch is applied?
  388. @item
  389. Did you provide an example so we can verify the new feature added by the
  390. patch easily?
  391. @item
  392. If you added a new file, did you insert a license header? It should be
  393. taken from FFmpeg, not randomly copied and pasted from somewhere else.
  394. @item
  395. You should maintain alphabetical order in alphabetically ordered lists as
  396. long as doing so does not break API/ABI compatibility.
  397. @item
  398. Lines with similar content should be aligned vertically when doing so
  399. improves readability.
  400. @item
  401. Consider to add a regression test for your code.
  402. @item
  403. If you added YASM code please check that things still work with --disable-yasm
  404. @end enumerate
  405. @section Patch review process
  406. All patches posted to ffmpeg-devel will be reviewed, unless they contain a
  407. clear note that the patch is not for the git master branch.
  408. Reviews and comments will be posted as replies to the patch on the
  409. mailing list. The patch submitter then has to take care of every comment,
  410. that can be by resubmitting a changed patch or by discussion. Resubmitted
  411. patches will themselves be reviewed like any other patch. If at some point
  412. a patch passes review with no comments then it is approved, that can for
  413. simple and small patches happen immediately while large patches will generally
  414. have to be changed and reviewed many times before they are approved.
  415. After a patch is approved it will be committed to the repository.
  416. We will review all submitted patches, but sometimes we are quite busy so
  417. especially for large patches this can take several weeks.
  418. If you feel that the review process is too slow and you are willing to try to
  419. take over maintainership of the area of code you change then just clone
  420. git master and maintain the area of code there. We will merge each area from
  421. where its best maintained.
  422. When resubmitting patches, please do not make any significant changes
  423. not related to the comments received during review. Such patches will
  424. be rejected. Instead, submit significant changes or new features as
  425. separate patches.
  426. @section Regression tests
  427. Before submitting a patch (or committing to the repository), you should at least
  428. test that you did not break anything.
  429. Running 'make fate' accomplishes this, please see @file{doc/fate.txt} for details.
  430. [Of course, some patches may change the results of the regression tests. In
  431. this case, the reference results of the regression tests shall be modified
  432. accordingly].
  433. @bye