mirror of
https://git.videolan.org/git/ffmpeg.git
synced 2024-09-08 08:55:34 +02:00
408 lines
16 KiB
Plaintext
408 lines
16 KiB
Plaintext
\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{libavcodec/apiexample.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{libavformat/output-example.c} to use it to generate
|
|
audio or video streams.
|
|
|
|
@end itemize
|
|
|
|
@section Integrating libav in your program
|
|
|
|
Shared libraries should be used whenever is possible in order to reduce
|
|
the effort distributors have to pour to support programs and to ensure
|
|
only the public api is used.
|
|
|
|
You can use Libav in your commercial program, but you must abide to the
|
|
license, LGPL or GPL depending on the specific features used, please refer
|
|
to @url{http://libav.org/legal.html} for a quick checklist and to
|
|
@url{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.GPLv2},
|
|
@url{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.GPLv3},
|
|
@url{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.LGPLv2.1},
|
|
@url{http://git.libav.org/?p=libav.git;a=blob;f=COPYING.LGPLv3} for the
|
|
exact text of the licenses.
|
|
Any modification to the source code can be suggested for inclusion.
|
|
The best way to proceed is to send your patches to the Libav mailing list.
|
|
|
|
@anchor{Coding Rules}
|
|
@section Coding Rules
|
|
|
|
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
|
|
|
|
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 GCC 2.95 and GCC 3.3. Currently, Libav also
|
|
compiles with several other compilers, such as the Compaq ccc compiler
|
|
or Sun Studio 9, and we would like to keep it that way unless it would
|
|
be exceedingly involved. To ensure compatibility, please do not use any
|
|
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
|
|
|
|
Indent size is 4.
|
|
The presentation is one inspired by 'indent -i4 -kr -nut'.
|
|
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.
|
|
|
|
The main priority in Libav is simplicity and small code size in order to
|
|
minimize the bug count.
|
|
|
|
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.
|
|
@example
|
|
/**
|
|
* @@file mpeg.c
|
|
* 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
|
|
|
|
fprintf and printf are forbidden in libavformat and libavcodec,
|
|
please use av_log() instead.
|
|
|
|
Casts should be used only when necessary. Unneeded parentheses
|
|
should also be avoided if they don't make the code easier to understand.
|
|
|
|
@section Development Policy
|
|
|
|
@enumerate
|
|
@item
|
|
Contributions should be licensed under the LGPL 2.1, including an
|
|
"or any later version" clause, or the MIT license. 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
|
|
@samp{topic: short description} as header, separated by a newline
|
|
from the body consting in few lines explaining the reason of the patch.
|
|
Referring to the issue on the bug tracker does not exempt to report an
|
|
excerpt of the bug.
|
|
@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 libav-devel and libav-commits mailing list.
|
|
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 doublecheck.
|
|
@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.
|
|
|
|
Note, some rules were borrowed from the MPlayer project.
|
|
|
|
@section Submitting patches
|
|
|
|
First, read the (@pxref{Coding Rules}) above if you did not yet, in particular
|
|
the rules regarding patch submission.
|
|
|
|
As stated already, 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 Libav to check your patch.
|
|
The tool is located in the tools directory.
|
|
|
|
Run the @pxref{Regression Tests} before submitting a patch in order to verify
|
|
it does not cause unexpected problems.
|
|
|
|
Patches should be posted as base64 encoded attachments (or any other
|
|
encoding which ensures that the patch will not be trashed during
|
|
transmission) to the libav-devel mailing list, see
|
|
@url{https://lists.libav.org/mailman/listinfo/libav-devel}
|
|
|
|
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()'). This kind of explanation should be the body of the
|
|
commit message.
|
|
|
|
Also please if you send several patches, send each patch as a separate mail,
|
|
do not attach several unrelated patches to the same mail.
|
|
|
|
Use @code{git send-email} when possible since it will properly send patches
|
|
without requiring extra care.
|
|
|
|
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, it will be
|
|
committed to the official Libav 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{avcodec.h} or @file{avformat.h}?
|
|
@item
|
|
Did you register it in @file{allcodecs.c} or @file{allformats.c}?
|
|
@item
|
|
Did you add the CodecID to @file{avcodec.h}?
|
|
@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 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}?
|
|
@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
|
|
Do the regression tests pass with the patch applied?
|
|
@item
|
|
Does @code{make checkheaders} pass with the patch applied?
|
|
@item
|
|
Is the patch against latest Libav git master branch?
|
|
@item
|
|
Are you subscribed to libav-devel?
|
|
(@url{https://lists.libav.org/mailman/listinfo/libav-devel}
|
|
the list is subscribers)
|
|
@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 and the noise bitstream filter. Your decoder or demuxer
|
|
should not crash or end in a (near) infinite loop 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.libav.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 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.
|
|
@item
|
|
Lines with similar content should be aligned vertically when doing so
|
|
improves readability.
|
|
@end enumerate
|
|
|
|
@section Patch review process
|
|
|
|
All patches posted to libav-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.
|
|
|
|
When resubmitting patches, if their size grew or during the review different
|
|
issues arisen please split the patch so each issue has a specific patch.
|
|
|
|
@anchor{Regression Tests}
|
|
@section Regression Tests
|
|
|
|
Before submitting a patch (or committing to the repository), you should at
|
|
least make sure that it does not break anything.
|
|
|
|
If the code changed has already a test present in FATE you should run it,
|
|
otherwise it is advised to add it.
|
|
|
|
Improvements to codec or demuxer might change the FATE results. Make sure
|
|
to commit the update reference with the change and to explain in the comment
|
|
why the expected result changed.
|
|
|
|
Please refer to @file{doc/fate.txt}.
|
|
|
|
@bye
|