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diff --git a/ffmpeg/doc/developer.texi b/ffmpeg/doc/developer.texi new file mode 100644 index 0000000..bd3f7a7 --- /dev/null +++ b/ffmpeg/doc/developer.texi @@ -0,0 +1,668 @@ +\input texinfo @c -*- texinfo -*- + +@settitle Developer Documentation +@titlepage +@center @titlefont{Developer Documentation} +@end titlepage + +@top + +@contents + +@chapter Developers Guide + +@section API +@itemize @bullet +@item libavcodec is the library containing the codecs (both encoding and +decoding). Look at @file{doc/examples/decoding_encoding.c} to see how to use +it. + +@item libavformat is the library containing the file format handling (mux and +demux code for several formats). Look at @file{ffplay.c} to use it in a +player. See @file{doc/examples/muxing.c} to use it to generate audio or video +streams. + +@end itemize + +@section Integrating libavcodec or libavformat in your program + +You can integrate all the source code of the libraries to link them +statically to avoid any version problem. All you need is to provide a +'config.mak' and a 'config.h' in the parent directory. See the defines +generated by ./configure to understand what is needed. + +You can use libavcodec or libavformat in your commercial program, but +@emph{any patch you make must be published}. The best way to proceed is +to send your patches to the FFmpeg mailing list. + +@section Contributing + +There are 3 ways by which code gets into ffmpeg. +@itemize @bullet +@item Submitting Patches to the main developer mailing list + see @ref{Submitting patches} for details. +@item Directly committing changes to the main tree. +@item Committing changes to a git clone, for example on github.com or + gitorious.org. And asking us to merge these changes. +@end itemize + +Whichever way, changes should be reviewed by the maintainer of the code +before they are committed. And they should follow the @ref{Coding Rules}. +The developer making the commit and the author are responsible for their changes +and should try to fix issues their commit causes. + +@anchor{Coding Rules} +@section Coding Rules + +@subsection Code formatting conventions + +There are the following guidelines regarding the indentation in files: +@itemize @bullet +@item +Indent size is 4. +@item +The TAB character is forbidden outside of Makefiles as is any +form of trailing whitespace. Commits containing either will be +rejected by the git repository. +@item +You should try to limit your code lines to 80 characters; however, do so if +and only if this improves readability. +@end itemize +The presentation is one inspired by 'indent -i4 -kr -nut'. + +The main priority in FFmpeg is simplicity and small code size in order to +minimize the bug count. + +@subsection Comments +Use the JavaDoc/Doxygen format (see examples below) so that code documentation +can be generated automatically. All nontrivial functions should have a comment +above them explaining what the function does, even if it is just one sentence. +All structures and their member variables should be documented, too. + +Avoid Qt-style and similar Doxygen syntax with @code{!} in it, i.e. replace +@code{//!} with @code{///} and similar. Also @@ syntax should be employed +for markup commands, i.e. use @code{@@param} and not @code{\param}. + +@example +/** + * @@file + * MPEG codec. + * @@author ... + */ + +/** + * Summary sentence. + * more text ... + * ... + */ +typedef struct Foobar@{ + int var1; /**< var1 description */ + int var2; ///< var2 description + /** var3 description */ + int var3; +@} Foobar; + +/** + * Summary sentence. + * more text ... + * ... + * @@param my_parameter description of my_parameter + * @@return return value description + */ +int myfunc(int my_parameter) +... +@end example + +@subsection C language features + +FFmpeg is programmed in the ISO C90 language with a few additional +features from ISO C99, namely: +@itemize @bullet +@item +the @samp{inline} keyword; +@item +@samp{//} comments; +@item +designated struct initializers (@samp{struct s x = @{ .i = 17 @};}) +@item +compound literals (@samp{x = (struct s) @{ 17, 23 @};}) +@end itemize + +These features are supported by all compilers we care about, so we will not +accept patches to remove their use unless they absolutely do not impair +clarity and performance. + +All code must compile with recent versions of GCC and a number of other +currently supported compilers. To ensure compatibility, please do not use +additional C99 features or GCC extensions. Especially watch out for: +@itemize @bullet +@item +mixing statements and declarations; +@item +@samp{long long} (use @samp{int64_t} instead); +@item +@samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar; +@item +GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}). +@end itemize + +@subsection Naming conventions +All names should be composed with underscores (_), not CamelCase. For example, +@samp{avfilter_get_video_buffer} is an acceptable function name and +@samp{AVFilterGetVideo} is not. The exception from this are type names, like +for example structs and enums; they should always be in the CamelCase + +There are the following conventions for naming variables and functions: +@itemize @bullet +@item +For local variables no prefix is required. +@item +For variables and functions declared as @code{static} no prefix is required. +@item +For variables and functions used internally by a library an @code{ff_} +prefix should be used, e.g. @samp{ff_w64_demuxer}. +@item +For variables and functions used internally across multiple libraries, use +@code{avpriv_}. For example, @samp{avpriv_aac_parse_header}. +@item +Each library has its own prefix for public symbols, in addition to the +commonly used @code{av_} (@code{avformat_} for libavformat, +@code{avcodec_} for libavcodec, @code{swr_} for libswresample, etc). +Check the existing code and choose names accordingly. +Note that some symbols without these prefixes are also exported for +retro-compatibility reasons. These exceptions are declared in the +@code{lib<name>/lib<name>.v} files. +@end itemize + +Furthermore, name space reserved for the system should not be invaded. +Identifiers ending in @code{_t} are reserved by +@url{http://pubs.opengroup.org/onlinepubs/007904975/functions/xsh_chap02_02.html#tag_02_02_02, POSIX}. +Also avoid names starting with @code{__} or @code{_} followed by an uppercase +letter as they are reserved by the C standard. Names starting with @code{_} +are reserved at the file level and may not be used for externally visible +symbols. If in doubt, just avoid names starting with @code{_} altogether. + +@subsection Miscellaneous conventions +@itemize @bullet +@item +fprintf and printf are forbidden in libavformat and libavcodec, +please use av_log() instead. +@item +Casts should be used only when necessary. Unneeded parentheses +should also be avoided if they don't make the code easier to understand. +@end itemize + +@subsection Editor configuration +In order to configure Vim to follow FFmpeg formatting conventions, paste +the following snippet into your @file{.vimrc}: +@example +" indentation rules for FFmpeg: 4 spaces, no tabs +set expandtab +set shiftwidth=4 +set softtabstop=4 +set cindent +set cinoptions=(0 +" Allow tabs in Makefiles. +autocmd FileType make,automake set noexpandtab shiftwidth=8 softtabstop=8 +" Trailing whitespace and tabs are forbidden, so highlight them. +highlight ForbiddenWhitespace ctermbg=red guibg=red +match ForbiddenWhitespace /\s\+$\|\t/ +" Do not highlight spaces at the end of line while typing on that line. +autocmd InsertEnter * match ForbiddenWhitespace /\t\|\s\+\%#\@@<!$/ +@end example + +For Emacs, add these roughly equivalent lines to your @file{.emacs.d/init.el}: +@example +(c-add-style "ffmpeg" + '("k&r" + (c-basic-offset . 4) + (indent-tabs-mode . nil) + (show-trailing-whitespace . t) + (c-offsets-alist + (statement-cont . (c-lineup-assignments +))) + ) + ) +(setq c-default-style "ffmpeg") +@end example + +@section Development Policy + +@enumerate +@item + Contributions should be licensed under the + @uref{http://www.gnu.org/licenses/lgpl-2.1.html, LGPL 2.1}, + including an "or any later version" clause, or, if you prefer + a gift-style license, the + @uref{http://www.isc.org/software/license/, ISC} or + @uref{http://mit-license.org/, MIT} license. + @uref{http://www.gnu.org/licenses/gpl-2.0.html, GPL 2} including + an "or any later version" clause is also acceptable, but LGPL is + preferred. +@item + You must not commit code which breaks FFmpeg! (Meaning unfinished but + enabled code which breaks compilation or compiles but does not work or + breaks the regression tests) + You can commit unfinished stuff (for testing etc), but it must be disabled + (#ifdef etc) by default so it does not interfere with other developers' + work. +@item + The commit message should have a short first line in the form of + a @samp{topic: short description} as a header, separated by a newline + from the body consisting of an explanation of why the change is necessary. + If the commit fixes a known bug on the bug tracker, the commit message + should include its bug ID. Referring to the issue on the bug tracker does + not exempt you from writing an excerpt of the bug in the commit message. +@item + You do not have to over-test things. If it works for you, and you think it + should work for others, then commit. If your code has problems + (portability, triggers compiler bugs, unusual environment etc) they will be + reported and eventually fixed. +@item + Do not commit unrelated changes together, split them into self-contained + pieces. Also do not forget that if part B depends on part A, but A does not + depend on B, then A can and should be committed first and separate from B. + Keeping changes well split into self-contained parts makes reviewing and + understanding them on the commit log mailing list easier. This also helps + in case of debugging later on. + Also if you have doubts about splitting or not splitting, do not hesitate to + ask/discuss it on the developer mailing list. +@item + Do not change behavior of the programs (renaming options etc) or public + API or ABI without first discussing it on the ffmpeg-devel mailing list. + Do not remove functionality from the code. Just improve! + + Note: Redundant code can be removed. +@item + Do not commit changes to the build system (Makefiles, configure script) + which change behavior, defaults etc, without asking first. The same + applies to compiler warning fixes, trivial looking fixes and to code + maintained by other developers. We usually have a reason for doing things + the way we do. Send your changes as patches to the ffmpeg-devel mailing + list, and if the code maintainers say OK, you may commit. This does not + apply to files you wrote and/or maintain. +@item + We refuse source indentation and other cosmetic changes if they are mixed + with functional changes, such commits will be rejected and removed. Every + developer has his own indentation style, you should not change it. Of course + if you (re)write something, you can use your own style, even though we would + prefer if the indentation throughout FFmpeg was consistent (Many projects + force a given indentation style - we do not.). If you really need to make + indentation changes (try to avoid this), separate them strictly from real + changes. + + NOTE: If you had to put if()@{ .. @} over a large (> 5 lines) chunk of code, + then either do NOT change the indentation of the inner part within (do not + move it to the right)! or do so in a separate commit +@item + Always fill out the commit log message. Describe in a few lines what you + changed and why. You can refer to mailing list postings if you fix a + particular bug. Comments such as "fixed!" or "Changed it." are unacceptable. + Recommended format: + area changed: Short 1 line description + + details describing what and why and giving references. +@item + Make sure the author of the commit is set correctly. (see git commit --author) + If you apply a patch, send an + answer to ffmpeg-devel (or wherever you got the patch from) saying that + you applied the patch. +@item + When applying patches that have been discussed (at length) on the mailing + list, reference the thread in the log message. +@item + Do NOT commit to code actively maintained by others without permission. + Send a patch to ffmpeg-devel instead. If no one answers within a reasonable + timeframe (12h for build failures and security fixes, 3 days small changes, + 1 week for big patches) then commit your patch if you think it is OK. + Also note, the maintainer can simply ask for more time to review! +@item + Subscribe to the ffmpeg-cvslog mailing list. The diffs of all commits + are sent there and reviewed by all the other developers. Bugs and possible + improvements or general questions regarding commits are discussed there. We + expect you to react if problems with your code are uncovered. +@item + Update the documentation if you change behavior or add features. If you are + unsure how best to do this, send a patch to ffmpeg-devel, the documentation + maintainer(s) will review and commit your stuff. +@item + Try to keep important discussions and requests (also) on the public + developer mailing list, so that all developers can benefit from them. +@item + Never write to unallocated memory, never write over the end of arrays, + always check values read from some untrusted source before using them + as array index or other risky things. +@item + Remember to check if you need to bump versions for the specific libav* + parts (libavutil, libavcodec, libavformat) you are changing. You need + to change the version integer. + Incrementing the first component means no backward compatibility to + previous versions (e.g. removal of a function from the public API). + Incrementing the second component means backward compatible change + (e.g. addition of a function to the public API or extension of an + existing data structure). + Incrementing the third component means a noteworthy binary compatible + change (e.g. encoder bug fix that matters for the decoder). The third + component always starts at 100 to distinguish FFmpeg from Libav. +@item + Compiler warnings indicate potential bugs or code with bad style. If a type of + warning always points to correct and clean code, that warning should + be disabled, not the code changed. + Thus the remaining warnings can either be bugs or correct code. + If it is a bug, the bug has to be fixed. If it is not, the code should + be changed to not generate a warning unless that causes a slowdown + or obfuscates the code. +@item + If you add a new file, give it a proper license header. Do not copy and + paste it from a random place, use an existing file as template. +@end enumerate + +We think our rules are not too hard. If you have comments, contact us. + +@anchor{Submitting patches} +@section Submitting patches + +First, read the @ref{Coding Rules} above if you did not yet, in particular +the rules regarding patch submission. + +When you submit your patch, please use @code{git format-patch} or +@code{git send-email}. We cannot read other diffs :-) + +Also please do not submit a patch which contains several unrelated changes. +Split it into separate, self-contained pieces. This does not mean splitting +file by file. Instead, make the patch as small as possible while still +keeping it as a logical unit that contains an individual change, even +if it spans multiple files. This makes reviewing your patches much easier +for us and greatly increases your chances of getting your patch applied. + +Use the patcheck tool of FFmpeg to check your patch. +The tool is located in the tools directory. + +Run the @ref{Regression tests} before submitting a patch in order to verify +it does not cause unexpected problems. + +It also helps quite a bit if you tell us what the patch does (for example +'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant +and has no lrint()') + +Also please if you send several patches, send each patch as a separate mail, +do not attach several unrelated patches to the same mail. + +Patches should be posted to the +@uref{http://lists.ffmpeg.org/mailman/listinfo/ffmpeg-devel, ffmpeg-devel} +mailing list. Use @code{git send-email} when possible since it will properly +send patches without requiring extra care. If you cannot, then send patches +as base64-encoded attachments, so your patch is not trashed during +transmission. + +Your patch will be reviewed on the mailing list. You will likely be asked +to make some changes and are expected to send in an improved version that +incorporates the requests from the review. This process may go through +several iterations. Once your patch is deemed good enough, some developer +will pick it up and commit it to the official FFmpeg tree. + +Give us a few days to react. But if some time passes without reaction, +send a reminder by email. Your patch should eventually be dealt with. + + +@section New codecs or formats checklist + +@enumerate +@item + Did you use av_cold for codec initialization and close functions? +@item + Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or + AVInputFormat/AVOutputFormat struct? +@item + Did you bump the minor version number (and reset the micro version + number) in @file{libavcodec/version.h} or @file{libavformat/version.h}? +@item + Did you register it in @file{allcodecs.c} or @file{allformats.c}? +@item + Did you add the AVCodecID to @file{avcodec.h}? + When adding new codec IDs, also add an entry to the codec descriptor + list in @file{libavcodec/codec_desc.c}. +@item + If it has a FourCC, did you add it to @file{libavformat/riff.c}, + even if it is only a decoder? +@item + Did you add a rule to compile the appropriate files in the Makefile? + Remember to do this even if you're just adding a format to a file that is + already being compiled by some other rule, like a raw demuxer. +@item + Did you add an entry to the table of supported formats or codecs in + @file{doc/general.texi}? +@item + Did you add an entry in the Changelog? +@item + If it depends on a parser or a library, did you add that dependency in + configure? +@item + Did you @code{git add} the appropriate files before committing? +@item + Did you make sure it compiles standalone, i.e. with + @code{configure --disable-everything --enable-decoder=foo} + (or @code{--enable-demuxer} or whatever your component is)? +@end enumerate + + +@section patch submission checklist + +@enumerate +@item + Does @code{make fate} pass with the patch applied? +@item + Was the patch generated with git format-patch or send-email? +@item + Did you sign off your patch? (git commit -s) + See @url{http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=blob_plain;f=Documentation/SubmittingPatches} for the meaning + of sign off. +@item + Did you provide a clear git commit log message? +@item + Is the patch against latest FFmpeg git master branch? +@item + Are you subscribed to ffmpeg-devel? + (the list is subscribers only due to spam) +@item + Have you checked that the changes are minimal, so that the same cannot be + achieved with a smaller patch and/or simpler final code? +@item + If the change is to speed critical code, did you benchmark it? +@item + If you did any benchmarks, did you provide them in the mail? +@item + Have you checked that the patch does not introduce buffer overflows or + other security issues? +@item + Did you test your decoder or demuxer against damaged data? If no, see + tools/trasher, the noise bitstream filter, and + @uref{http://caca.zoy.org/wiki/zzuf, zzuf}. Your decoder or demuxer + should not crash, end in a (near) infinite loop, or allocate ridiculous + amounts of memory when fed damaged data. +@item + Does the patch not mix functional and cosmetic changes? +@item + Did you add tabs or trailing whitespace to the code? Both are forbidden. +@item + Is the patch attached to the email you send? +@item + Is the mime type of the patch correct? It should be text/x-diff or + text/x-patch or at least text/plain and not application/octet-stream. +@item + If the patch fixes a bug, did you provide a verbose analysis of the bug? +@item + If the patch fixes a bug, did you provide enough information, including + a sample, so the bug can be reproduced and the fix can be verified? + Note please do not attach samples >100k to mails but rather provide a + URL, you can upload to ftp://upload.ffmpeg.org +@item + Did you provide a verbose summary about what the patch does change? +@item + Did you provide a verbose explanation why it changes things like it does? +@item + Did you provide a verbose summary of the user visible advantages and + disadvantages if the patch is applied? +@item + Did you provide an example so we can verify the new feature added by the + patch easily? +@item + If you added a new file, did you insert a license header? It should be + taken from FFmpeg, not randomly copied and pasted from somewhere else. +@item + You should maintain alphabetical order in alphabetically ordered lists as + long as doing so does not break API/ABI compatibility. +@item + Lines with similar content should be aligned vertically when doing so + improves readability. +@item + Consider to add a regression test for your code. +@item + If you added YASM code please check that things still work with --disable-yasm +@item + Make sure you check the return values of function and return appropriate + error codes. Especially memory allocation functions like @code{av_malloc()} + are notoriously left unchecked, which is a serious problem. +@item + Test your code with valgrind and or Address Sanitizer to ensure it's free + of leaks, out of array accesses, etc. +@end enumerate + +@section Patch review process + +All patches posted to ffmpeg-devel will be reviewed, unless they contain a +clear note that the patch is not for the git master branch. +Reviews and comments will be posted as replies to the patch on the +mailing list. The patch submitter then has to take care of every comment, +that can be by resubmitting a changed patch or by discussion. Resubmitted +patches will themselves be reviewed like any other patch. If at some point +a patch passes review with no comments then it is approved, that can for +simple and small patches happen immediately while large patches will generally +have to be changed and reviewed many times before they are approved. +After a patch is approved it will be committed to the repository. + +We will review all submitted patches, but sometimes we are quite busy so +especially for large patches this can take several weeks. + +If you feel that the review process is too slow and you are willing to try to +take over maintainership of the area of code you change then just clone +git master and maintain the area of code there. We will merge each area from +where its best maintained. + +When resubmitting patches, please do not make any significant changes +not related to the comments received during review. Such patches will +be rejected. Instead, submit significant changes or new features as +separate patches. + +@anchor{Regression tests} +@section Regression tests + +Before submitting a patch (or committing to the repository), you should at least +test that you did not break anything. + +Running 'make fate' accomplishes this, please see @url{fate.html} for details. + +[Of course, some patches may change the results of the regression tests. In +this case, the reference results of the regression tests shall be modified +accordingly]. + +@subsection Adding files to the fate-suite dataset + +When there is no muxer or encoder available to generate test media for a +specific test then the media has to be inlcuded in the fate-suite. +First please make sure that the sample file is as small as possible to test the +respective decoder or demuxer sufficiently. Large files increase network +bandwidth and disk space requirements. +Once you have a working fate test and fate sample, provide in the commit +message or introductionary message for the patch series that you post to +the ffmpeg-devel mailing list, a direct link to download the sample media. + + +@anchor{Release process} +@section Release process + +FFmpeg maintains a set of @strong{release branches}, which are the +recommended deliverable for system integrators and distributors (such as +Linux distributions, etc.). At regular times, a @strong{release +manager} prepares, tests and publishes tarballs on the +@url{http://ffmpeg.org} website. + +There are two kinds of releases: + +@enumerate +@item + @strong{Major releases} always include the latest and greatest + features and functionality. +@item + @strong{Point releases} are cut from @strong{release} branches, + which are named @code{release/X}, with @code{X} being the release + version number. +@end enumerate + +Note that we promise to our users that shared libraries from any FFmpeg +release never break programs that have been @strong{compiled} against +previous versions of @strong{the same release series} in any case! + +However, from time to time, we do make API changes that require adaptations +in applications. Such changes are only allowed in (new) major releases and +require further steps such as bumping library version numbers and/or +adjustments to the symbol versioning file. Please discuss such changes +on the @strong{ffmpeg-devel} mailing list in time to allow forward planning. + +@anchor{Criteria for Point Releases} +@subsection Criteria for Point Releases + +Changes that match the following criteria are valid candidates for +inclusion into a point release: + +@enumerate +@item + Fixes a security issue, preferably identified by a @strong{CVE + number} issued by @url{http://cve.mitre.org/}. +@item + Fixes a documented bug in @url{https://ffmpeg.org/trac/ffmpeg}. +@item + Improves the included documentation. +@item + Retains both source code and binary compatibility with previous + point releases of the same release branch. +@end enumerate + +The order for checking the rules is (1 OR 2 OR 3) AND 4. + + +@subsection Release Checklist + +The release process involves the following steps: + +@enumerate +@item + Ensure that the @file{RELEASE} file contains the version number for + the upcoming release. +@item + Add the release at @url{https://ffmpeg.org/trac/ffmpeg/admin/ticket/versions}. +@item + Announce the intent to do a release to the mailing list. +@item + Make sure all relevant security fixes have been backported. See + @url{https://ffmpeg.org/security.html}. +@item + Ensure that the FATE regression suite still passes in the release + branch on at least @strong{i386} and @strong{amd64} + (cf. @ref{Regression tests}). +@item + Prepare the release tarballs in @code{bz2} and @code{gz} formats, and + supplementing files that contain @code{gpg} signatures +@item + Publish the tarballs at @url{http://ffmpeg.org/releases}. Create and + push an annotated tag in the form @code{nX}, with @code{X} + containing the version number. +@item + Propose and send a patch to the @strong{ffmpeg-devel} mailing list + with a news entry for the website. +@item + Publish the news entry. +@item + Send announcement to the mailing list. +@end enumerate + +@bye |