developer.texi 18 KB

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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. @anchor{Coding Rules}
  27. @section Coding Rules
  28. FFmpeg is programmed in the ISO C90 language with a few additional
  29. features from ISO C99, namely:
  30. @itemize @bullet
  31. @item
  32. the @samp{inline} keyword;
  33. @item
  34. @samp{//} comments;
  35. @item
  36. designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
  37. @item
  38. compound literals (@samp{x = (struct s) @{ 17, 23 @};})
  39. @end itemize
  40. These features are supported by all compilers we care about, so we will not
  41. accept patches to remove their use unless they absolutely do not impair
  42. clarity and performance.
  43. All code must compile with recent versions of GCC and a number of other
  44. currently supported compilers. To ensure compatibility, please do not use
  45. additional C99 features or GCC extensions. Especially watch out for:
  46. @itemize @bullet
  47. @item
  48. mixing statements and declarations;
  49. @item
  50. @samp{long long} (use @samp{int64_t} instead);
  51. @item
  52. @samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;
  53. @item
  54. GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
  55. @end itemize
  56. Indent size is 4.
  57. The presentation is one inspired by 'indent -i4 -kr -nut'.
  58. The TAB character is forbidden outside of Makefiles as is any
  59. form of trailing whitespace. Commits containing either will be
  60. rejected by the git repository.
  61. The main priority in FFmpeg is simplicity and small code size in order to
  62. minimize the bug count.
  63. Comments: Use the JavaDoc/Doxygen
  64. format (see examples below) so that code documentation
  65. can be generated automatically. All nontrivial functions should have a comment
  66. above them explaining what the function does, even if it is just one sentence.
  67. All structures and their member variables should be documented, too.
  68. @example
  69. /**
  70. * @@file
  71. * MPEG codec.
  72. * @@author ...
  73. */
  74. /**
  75. * Summary sentence.
  76. * more text ...
  77. * ...
  78. */
  79. typedef struct Foobar@{
  80. int var1; /**< var1 description */
  81. int var2; ///< var2 description
  82. /** var3 description */
  83. int var3;
  84. @} Foobar;
  85. /**
  86. * Summary sentence.
  87. * more text ...
  88. * ...
  89. * @@param my_parameter description of my_parameter
  90. * @@return return value description
  91. */
  92. int myfunc(int my_parameter)
  93. ...
  94. @end example
  95. fprintf and printf are forbidden in libavformat and libavcodec,
  96. please use av_log() instead.
  97. Casts should be used only when necessary. Unneeded parentheses
  98. should also be avoided if they don't make the code easier to understand.
  99. @section Development Policy
  100. @enumerate
  101. @item
  102. Contributions should be licensed under the LGPL 2.1, including an
  103. "or any later version" clause, or the MIT license. GPL 2 including
  104. an "or any later version" clause is also acceptable, but LGPL is
  105. preferred.
  106. @item
  107. You must not commit code which breaks FFmpeg! (Meaning unfinished but
  108. enabled code which breaks compilation or compiles but does not work or
  109. breaks the regression tests)
  110. You can commit unfinished stuff (for testing etc), but it must be disabled
  111. (#ifdef etc) by default so it does not interfere with other developers'
  112. work.
  113. @item
  114. You do not have to over-test things. If it works for you, and you think it
  115. should work for others, then commit. If your code has problems
  116. (portability, triggers compiler bugs, unusual environment etc) they will be
  117. reported and eventually fixed.
  118. @item
  119. Do not commit unrelated changes together, split them into self-contained
  120. pieces. Also do not forget that if part B depends on part A, but A does not
  121. depend on B, then A can and should be committed first and separate from B.
  122. Keeping changes well split into self-contained parts makes reviewing and
  123. understanding them on the commit log mailing list easier. This also helps
  124. in case of debugging later on.
  125. Also if you have doubts about splitting or not splitting, do not hesitate to
  126. ask/discuss it on the developer mailing list.
  127. @item
  128. Do not change behavior of the programs (renaming options etc) or public
  129. API or ABI without first discussing it on the ffmpeg-devel mailing list.
  130. Do not remove functionality from the code. Just improve!
  131. Note: Redundant code can be removed.
  132. @item
  133. Do not commit changes to the build system (Makefiles, configure script)
  134. which change behavior, defaults etc, without asking first. The same
  135. applies to compiler warning fixes, trivial looking fixes and to code
  136. maintained by other developers. We usually have a reason for doing things
  137. the way we do. Send your changes as patches to the ffmpeg-devel mailing
  138. list, and if the code maintainers say OK, you may commit. This does not
  139. apply to files you wrote and/or maintain.
  140. @item
  141. We refuse source indentation and other cosmetic changes if they are mixed
  142. with functional changes, such commits will be rejected and removed. Every
  143. developer has his own indentation style, you should not change it. Of course
  144. if you (re)write something, you can use your own style, even though we would
  145. prefer if the indentation throughout FFmpeg was consistent (Many projects
  146. force a given indentation style - we do not.). If you really need to make
  147. indentation changes (try to avoid this), separate them strictly from real
  148. changes.
  149. NOTE: If you had to put if()@{ .. @} over a large (> 5 lines) chunk of code,
  150. then either do NOT change the indentation of the inner part within (do not
  151. move it to the right)! or do so in a separate commit
  152. @item
  153. Always fill out the commit log message. Describe in a few lines what you
  154. changed and why. You can refer to mailing list postings if you fix a
  155. particular bug. Comments such as "fixed!" or "Changed it." are unacceptable.
  156. Recommanded format:
  157. area changed: Short 1 line description
  158. details describing what and why and giving references.
  159. @item
  160. Make sure the author of the commit is set correctly. (see git commit --author)
  161. If you apply a patch, send an
  162. answer to ffmpeg-devel (or wherever you got the patch from) saying that
  163. you applied the patch.
  164. @item
  165. When applying patches that have been discussed (at length) on the mailing
  166. list, reference the thread in the log message.
  167. @item
  168. Do NOT commit to code actively maintained by others without permission.
  169. Send a patch to ffmpeg-devel instead. If no one answers within a reasonable
  170. timeframe (12h for build failures and security fixes, 3 days small changes,
  171. 1 week for big patches) then commit your patch if you think it is OK.
  172. Also note, the maintainer can simply ask for more time to review!
  173. @item
  174. Subscribe to the ffmpeg-cvslog mailing list. The diffs of all commits
  175. are sent there and reviewed by all the other developers. Bugs and possible
  176. improvements or general questions regarding commits are discussed there. We
  177. expect you to react if problems with your code are uncovered.
  178. @item
  179. Update the documentation if you change behavior or add features. If you are
  180. unsure how best to do this, send a patch to ffmpeg-devel, the documentation
  181. maintainer(s) will review and commit your stuff.
  182. @item
  183. Try to keep important discussions and requests (also) on the public
  184. developer mailing list, so that all developers can benefit from them.
  185. @item
  186. Never write to unallocated memory, never write over the end of arrays,
  187. always check values read from some untrusted source before using them
  188. as array index or other risky things.
  189. @item
  190. Remember to check if you need to bump versions for the specific libav
  191. parts (libavutil, libavcodec, libavformat) you are changing. You need
  192. to change the version integer.
  193. Incrementing the first component means no backward compatibility to
  194. previous versions (e.g. removal of a function from the public API).
  195. Incrementing the second component means backward compatible change
  196. (e.g. addition of a function to the public API or extension of an
  197. existing data structure).
  198. Incrementing the third component means a noteworthy binary compatible
  199. change (e.g. encoder bug fix that matters for the decoder).
  200. @item
  201. Compiler warnings indicate potential bugs or code with bad style. If a type of
  202. warning always points to correct and clean code, that warning should
  203. be disabled, not the code changed.
  204. Thus the remaining warnings can either be bugs or correct code.
  205. If it is a bug, the bug has to be fixed. If it is not, the code should
  206. be changed to not generate a warning unless that causes a slowdown
  207. or obfuscates the code.
  208. @item
  209. If you add a new file, give it a proper license header. Do not copy and
  210. paste it from a random place, use an existing file as template.
  211. @end enumerate
  212. We think our rules are not too hard. If you have comments, contact us.
  213. Note, these rules are mostly borrowed from the MPlayer project.
  214. @section Submitting patches
  215. First, read the @ref{Coding Rules} above if you did not yet, in particular
  216. the rules regarding patch submission.
  217. When you submit your patch, please use @code{git format-patch} or
  218. @code{git send-email}. We cannot read other diffs :-)
  219. Also please do not submit a patch which contains several unrelated changes.
  220. Split it into separate, self-contained pieces. This does not mean splitting
  221. file by file. Instead, make the patch as small as possible while still
  222. keeping it as a logical unit that contains an individual change, even
  223. if it spans multiple files. This makes reviewing your patches much easier
  224. for us and greatly increases your chances of getting your patch applied.
  225. Use the patcheck tool of FFmpeg to check your patch.
  226. The tool is located in the tools directory.
  227. Run the @ref{Regression Tests} before submitting a patch in order to verify
  228. it does not cause unexpected problems.
  229. Patches should be posted as base64 encoded attachments (or any other
  230. encoding which ensures that the patch will not be trashed during
  231. transmission) to the ffmpeg-devel mailing list, see
  232. @url{http://lists.ffmpeg.org/mailman/listinfo/ffmpeg-devel}
  233. It also helps quite a bit if you tell us what the patch does (for example
  234. 'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
  235. and has no lrint()')
  236. Also please if you send several patches, send each patch as a separate mail,
  237. do not attach several unrelated patches to the same mail.
  238. Your patch will be reviewed on the mailing list. You will likely be asked
  239. to make some changes and are expected to send in an improved version that
  240. incorporates the requests from the review. This process may go through
  241. several iterations. Once your patch is deemed good enough, some developer
  242. will pick it up and commit it to the official FFmpeg tree.
  243. Give us a few days to react. But if some time passes without reaction,
  244. send a reminder by email. Your patch should eventually be dealt with.
  245. @section New codecs or formats checklist
  246. @enumerate
  247. @item
  248. Did you use av_cold for codec initialization and close functions?
  249. @item
  250. Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
  251. AVInputFormat/AVOutputFormat struct?
  252. @item
  253. Did you bump the minor version number (and reset the micro version
  254. number) in @file{avcodec.h} or @file{avformat.h}?
  255. @item
  256. Did you register it in @file{allcodecs.c} or @file{allformats.c}?
  257. @item
  258. Did you add the CodecID to @file{avcodec.h}?
  259. @item
  260. If it has a fourcc, did you add it to @file{libavformat/riff.c},
  261. even if it is only a decoder?
  262. @item
  263. Did you add a rule to compile the appropriate files in the Makefile?
  264. Remember to do this even if you're just adding a format to a file that is
  265. already being compiled by some other rule, like a raw demuxer.
  266. @item
  267. Did you add an entry to the table of supported formats or codecs in
  268. @file{doc/general.texi}?
  269. @item
  270. Did you add an entry in the Changelog?
  271. @item
  272. If it depends on a parser or a library, did you add that dependency in
  273. configure?
  274. @item
  275. Did you @code{git add} the appropriate files before committing?
  276. @item
  277. Did you make sure it compiles standalone, i.e. with
  278. @code{configure --disable-everything --enable-decoder=foo}
  279. (or @code{--enable-demuxer} or whatever your component is)?
  280. @end enumerate
  281. @section patch submission checklist
  282. @enumerate
  283. @item
  284. Does 'make fate' pass with the patch applied?
  285. @item
  286. Was the patch generated with git format-patch or send-email?
  287. @item
  288. Did you sign off your patch? (git commit -s)
  289. See @url{http://kerneltrap.org/files/Jeremy/DCO.txt} for the meaning
  290. of sign off.
  291. @item
  292. Did you provide a clear git commit log message?
  293. @item
  294. Is the patch against latest FFmpeg git master branch?
  295. @item
  296. Are you subscribed to ffmpeg-devel?
  297. (the list is subscribers only due to spam)
  298. @item
  299. Have you checked that the changes are minimal, so that the same cannot be
  300. achieved with a smaller patch and/or simpler final code?
  301. @item
  302. If the change is to speed critical code, did you benchmark it?
  303. @item
  304. If you did any benchmarks, did you provide them in the mail?
  305. @item
  306. Have you checked that the patch does not introduce buffer overflows or
  307. other security issues?
  308. @item
  309. Did you test your decoder or demuxer against damaged data? If no, see
  310. tools/trasher and the noise bitstream filter. Your decoder or demuxer
  311. should not crash or end in a (near) infinite loop when fed damaged data.
  312. @item
  313. Does the patch not mix functional and cosmetic changes?
  314. @item
  315. Did you add tabs or trailing whitespace to the code? Both are forbidden.
  316. @item
  317. Is the patch attached to the email you send?
  318. @item
  319. Is the mime type of the patch correct? It should be text/x-diff or
  320. text/x-patch or at least text/plain and not application/octet-stream.
  321. @item
  322. If the patch fixes a bug, did you provide a verbose analysis of the bug?
  323. @item
  324. If the patch fixes a bug, did you provide enough information, including
  325. a sample, so the bug can be reproduced and the fix can be verified?
  326. Note please do not attach samples >100k to mails but rather provide a
  327. URL, you can upload to ftp://upload.ffmpeg.org
  328. @item
  329. Did you provide a verbose summary about what the patch does change?
  330. @item
  331. Did you provide a verbose explanation why it changes things like it does?
  332. @item
  333. Did you provide a verbose summary of the user visible advantages and
  334. disadvantages if the patch is applied?
  335. @item
  336. Did you provide an example so we can verify the new feature added by the
  337. patch easily?
  338. @item
  339. If you added a new file, did you insert a license header? It should be
  340. taken from FFmpeg, not randomly copied and pasted from somewhere else.
  341. @item
  342. You should maintain alphabetical order in alphabetically ordered lists as
  343. long as doing so does not break API/ABI compatibility.
  344. @item
  345. Lines with similar content should be aligned vertically when doing so
  346. improves readability.
  347. @item
  348. Consider to add a regression test for your code.
  349. @item
  350. If you added YASM code please check that things still work with --disable-yasm
  351. @end enumerate
  352. @section Patch review process
  353. All patches posted to ffmpeg-devel will be reviewed, unless they contain a
  354. clear note that the patch is not for the git master branch.
  355. Reviews and comments will be posted as replies to the patch on the
  356. mailing list. The patch submitter then has to take care of every comment,
  357. that can be by resubmitting a changed patch or by discussion. Resubmitted
  358. patches will themselves be reviewed like any other patch. If at some point
  359. a patch passes review with no comments then it is approved, that can for
  360. simple and small patches happen immediately while large patches will generally
  361. have to be changed and reviewed many times before they are approved.
  362. After a patch is approved it will be committed to the repository.
  363. We will review all submitted patches, but sometimes we are quite busy so
  364. especially for large patches this can take several weeks.
  365. When resubmitting patches, please do not make any significant changes
  366. not related to the comments received during review. Such patches will
  367. be rejected. Instead, submit significant changes or new features as
  368. separate patches.
  369. @section Regression tests
  370. Before submitting a patch (or committing to the repository), you should at least
  371. test that you did not break anything.
  372. The regression tests build a synthetic video stream and a synthetic
  373. audio stream. These are then encoded and decoded with all codecs or
  374. formats. The CRC (or MD5) of each generated file is recorded in a
  375. result file. A 'diff' is launched to compare the reference results and
  376. the result file. The output is checked immediately after each test
  377. has run.
  378. The regression tests then go on to test the FFserver code with a
  379. limited set of streams. It is important that this step runs correctly
  380. as well.
  381. Run 'make test' to test all the codecs and formats. Commands like
  382. 'make regtest-mpeg2' can be used to run a single test. By default,
  383. make will abort if any test fails. To run all tests regardless,
  384. use make -k. To get a more verbose output, use 'make V=1 test' or
  385. 'make V=2 test'.
  386. Run 'make fulltest' to test all the codecs, formats and FFserver.
  387. [Of course, some patches may change the results of the regression tests. In
  388. this case, the reference results of the regression tests shall be modified
  389. accordingly].
  390. @bye