@chapter Developers Guide
@section API
+
@itemize @bullet
@item libavcodec is the library containing the codecs (both encoding and
decoding). Look at @file{libavcodec/apiexample.c} to see how to use it.
demux code for several formats). Look at @file{avplay.c} to use it in a
player. See @file{libavformat/output-example.c} to use it to generate
audio or video streams.
-
@end itemize
@section Integrating libav in your program
@subsection Code formatting conventions
The code is written in K&R C style. That means the following:
+
@itemize @bullet
@item
The control statements are formatted by putting space between the statement
@example
for (i = 0; i < filter->input_count; i++) @{
@end example
+
@item
The case statement is always located at the same level as the switch itself:
@example
av_log(filter, AV_LOG_INFO, "circular filter chain detected");
return 0;
@end example
+
@item
Braces in function declarations are written on the new line:
@example
return LIBAV_CONFIGURATION;
@}
@end example
+
@item
Do not check for NULL values by comparison, @samp{if (p)} and
@samp{if (!p)} are correct; @samp{if (p == NULL)} and @samp{if (p != NULL)}
are not.
+
@item
In case of a single-statement if, no curly braces are required:
@example
if (!pic || !picref)
goto fail;
@end example
+
@item
Do not put spaces immediately inside parentheses. @samp{if (ret)} is
a valid style; @samp{if ( ret )} is not.
@end itemize
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.
Libav 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
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
names; they should always be CamelCase.
There are the following conventions for naming variables and functions:
+
@itemize @bullet
@item
For local variables no prefix is required.
+
@item
For file-scope variables and functions declared as @code{static}, no prefix
is required.
+
@item
For variables and functions visible outside of file scope, but only used
internally by a library, an @code{ff_} prefix should be used,
e.g. @samp{ff_w64_demuxer}.
+
@item
For variables and functions visible outside of file scope, used internally
across multiple libraries, use @code{avpriv_} as prefix, for example,
@samp{avpriv_aac_parse_header}.
+
@item
For externally visible symbols, each library has its own prefix. Check
the existing code and choose names accordingly.
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.
@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
- All the patches MUST be reviewed in the mailing list before they are
- committed.
-@item
- The Libav coding style should remain consistent. Changes to
- conform will be suggested during the review or implemented on commit.
-@item
- Patches should be generated using @code{git format-patch} or directly sent
- using @code{git send-email}.
- Please make sure you give the proper credit by setting the correct author
- in the commit.
-@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.
- If the patch is a bug fix which should be backported to stable releases,
- i.e. a non-API/ABI-breaking bug fix, add @code{CC: libav-stable@@libav.org}
- to the bottom of your commit message, and make sure to CC your patch to
- this address, too. Some git setups will do this automatically.
-@item
- Work in progress patches should be sent to the mailing list with the [WIP]
- or the [RFC] tag.
-@item
- Branches in public personal repos are advised as way to
- work on issues collaboratively.
-@item
- You do not have to over-test things. If it works for you and you think it
- should work for others, send it to the mailing list for review.
- If you have doubt about portability please state it in the submission so
- people with specific hardware could test it.
-@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.
-@item
- Patches that change behavior of the programs (renaming options etc) or
- public API or ABI should be discussed in depth and possible few days should
- pass between discussion and commit.
- Changes to the build system (Makefiles, configure script) which alter
- the expected behavior should be considered in the same regard.
-@item
- When applying patches that have been discussed (at length) on the mailing
- list, reference the thread in the log message.
-@item
- Subscribe to the
- @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel} and
- @uref{https://lists.libav.org/mailman/listinfo/libav-commits, libav-commits}
- mailing lists.
- Bugs and possible improvements or general questions regarding commits
- are discussed on libav-devel. 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 an [RFC] patch to libav-devel.
-@item
- All discussions and decisions should be reported on the public developer
- mailing list, so that there is a reference to them.
- Other media (e.g. IRC) should be used for coordination and immediate
- collaboration.
-@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. Always use valgrind to double-check.
-@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).
-@item
- Compiler warnings indicate potential bugs or code with bad style.
- 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.
- If a type of warning leads to too many false positives, that warning
- should be disabled, not the code changed.
-@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.
+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
+All the patches MUST be reviewed in the mailing list before they are
+committed.
+
+@item
+The Libav coding style should remain consistent. Changes to
+conform will be suggested during the review or implemented on commit.
+
+@item
+Patches should be generated using @code{git format-patch} or directly sent
+using @code{git send-email}.
+Please make sure you give the proper credit by setting the correct author
+in the commit.
+
+@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.
+If the patch is a bug fix which should be backported to stable releases,
+i.e. a non-API/ABI-breaking bug fix, add @code{CC: libav-stable@@libav.org}
+to the bottom of your commit message, and make sure to CC your patch to
+this address, too. Some git setups will do this automatically.
+
+@item
+Work in progress patches should be sent to the mailing list with the [WIP]
+or the [RFC] tag.
+
+@item
+Branches in public personal repos are advised as way to
+work on issues collaboratively.
+
+@item
+You do not have to over-test things. If it works for you and you think it
+should work for others, send it to the mailing list for review.
+If you have doubt about portability please state it in the submission so
+people with specific hardware could test it.
+
+@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.
+
+@item
+Patches that change behavior of the programs (renaming options etc) or
+public API or ABI should be discussed in depth and possible few days should
+pass between discussion and commit.
+Changes to the build system (Makefiles, configure script) which alter
+the expected behavior should be considered in the same regard.
+
+@item
+When applying patches that have been discussed (at length) on the mailing
+list, reference the thread in the log message.
+
+@item
+Subscribe to the
+@uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel} and
+@uref{https://lists.libav.org/mailman/listinfo/libav-commits, libav-commits}
+mailing lists.
+Bugs and possible improvements or general questions regarding commits
+are discussed on libav-devel. 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 an [RFC] patch to libav-devel.
+
+@item
+All discussions and decisions should be reported on the public developer
+mailing list, so that there is a reference to them.
+Other media (e.g. IRC) should be used for coordination and immediate
+collaboration.
+
+@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. Always use valgrind to double-check.
+
+@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).
+
+@item
+Compiler warnings indicate potential bugs or code with bad style.
+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.
+If a type of warning leads to too many false positives, that warning
+should be disabled, not the code changed.
+
+@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.
@enumerate
@item
- Did you use av_cold for codec initialization and close functions?
+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?
+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}?
+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}?
+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}.
+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?
+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 are just adding a format to a file that
- is already being compiled by some other rule, like a raw demuxer.
+Did you add a rule to compile the appropriate files in the Makefile?
+Remember to do this even if you are 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}?
+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?
+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?
+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?
+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)?
+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
@enumerate
@item
- Does @code{make check} pass with the patch applied?
+Does @code{make check} pass with the patch applied?
+
@item
- Is the patch against latest Libav git master branch?
+Is the patch against latest Libav git master branch?
+
@item
- Are you subscribed to the
- @uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
- mailing list? (Only list subscribers are allowed to post.)
+Are you subscribed to the
+@uref{https://lists.libav.org/mailman/listinfo/libav-devel, libav-devel}
+mailing list? (Only list subscribers are allowed to post.)
+
@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?
+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?
+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?
+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?
+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.
+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?
+Does the patch not mix functional and cosmetic changes?
+
@item
- Did you add tabs or trailing whitespace to the code? Both are forbidden.
+Did you add tabs or trailing whitespace to the code? Both are forbidden.
+
@item
- Is the patch attached to the email you send?
+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.
+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?
+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.libav.org
+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.libav.org
+
@item
- Did you provide a verbose summary about what the patch does change?
+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?
+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?
+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?
+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 Libav, not randomly copied and pasted from somewhere else.
+If you added a new file, did you insert a license header? It should be
+taken from Libav, 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.
+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.
+Lines with similar content should be aligned vertically when doing so
+improves readability.
+
@item
- Make sure you check the return values of function and return appropriate
- error codes. Especially memory allocation functions like @code{malloc()}
- are notoriously left unchecked, which is a serious problem.
+Make sure you check the return values of function and return appropriate
+error codes. Especially memory allocation functions like @code{malloc()}
+are notoriously left unchecked, which is a serious problem.
@end enumerate
@section Patch review process
@item
Configure to compile with instrumentation enabled:
@code{configure --toolchain=gcov}.
+
@item
Run your test case, either manually or via FATE. This can be either
the full FATE regression suite, or any arbitrary invocation of any
front-end tool provided by Libav, in any combination.
+
@item
Run @code{make lcov} to generate coverage data in HTML format.
+
@item
View @code{lcov/index.html} in your preferred HTML viewer.
@end enumerate
@enumerate
@item
- @strong{Major releases} always include the latest and greatest
- features and functionality.
+@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.
+@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 Libav
@enumerate
@item
- Fixes a security issue, preferably identified by a @strong{CVE
- number} issued by @url{http://cve.mitre.org/}.
+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{http://bugzilla.libav.org}.
+Fixes a documented bug in @url{http://bugzilla.libav.org}.
+
@item
- Improves the included documentation.
+Improves the included documentation.
+
@item
- Retains both source code and binary compatibility with previous
- point releases of the same release branch.
+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.
@enumerate
@item
- Ensure that the @file{RELEASE} file contains the version number for
- the upcoming release.
+Ensure that the @file{RELEASE} file contains the version number for
+the upcoming release.
+
@item
- File a release tracking bug in @url{http://bugzilla.libav.org}. Make
- sure that the bug has an alias named @code{ReleaseX.Y} for the
- @code{X.Y} release.
+File a release tracking bug in @url{http://bugzilla.libav.org}. Make
+sure that the bug has an alias named @code{ReleaseX.Y} for the
+@code{X.Y} release.
+
@item
- Announce the intent to do a release to the mailing list.
+Announce the intent to do a release to the mailing list.
+
@item
- Reassign unresolved blocking bugs from previous release
- tracking bugs to the new bug.
+Reassign unresolved blocking bugs from previous release
+tracking bugs to the new bug.
+
@item
- Review patch nominations that reach the @strong{libav-stable}
- mailing list, and push patches that fulfill the stable release
- criteria to the release branch.
+Review patch nominations that reach the @strong{libav-stable}
+mailing list, and push patches that fulfill the stable release
+criteria to the release branch.
+
@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}).
+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{xz} and @code{gz} formats, and
- supplementing files that contain @code{md5} and @code{sha1}
- checksums.
+Prepare the release tarballs in @code{xz} and @code{gz} formats, and
+supplementing files that contain @code{md5} and @code{sha1}
+checksums.
+
@item
- Publish the tarballs at @url{http://libav.org/releases}. Create and
- push an annotated tag in the form @code{vX}, with @code{X}
- containing the version number.
+Publish the tarballs at @url{http://libav.org/releases}. Create and
+push an annotated tag in the form @code{vX}, with @code{X}
+containing the version number.
+
@item
- Build the tarballs with the Windows binaries, and publish them at
- @url{http://win32.libav.org/releases}.
+Build the tarballs with the Windows binaries, and publish them at
+@url{http://win32.libav.org/releases}.
+
@item
- Propose and send a patch to the @strong{libav-devel} mailing list
- with a news entry for the website.
+Propose and send a patch to the @strong{libav-devel} mailing list
+with a news entry for the website.
+
@item
- Publish the news entry.
+Publish the news entry.
+
@item
- Send announcement to the mailing list.
+Send announcement to the mailing list.
@end enumerate
@bye
projects / platform / upstream / libav.git / commitdiff