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Developer Documentation
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<h1>
Developer Documentation
</h1>
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</div>
<a name="SEC_Top"></a>
<div class="Contents_element" id="SEC_Contents">
<h2 class="contents-heading">Table of Contents</h2>
<div class="contents">
<ul class="no-bullet">
<li><a id="toc-Introduction" href="#Introduction">1 Introduction</a>
<ul class="no-bullet">
<li><a id="toc-Contributing-code" href="#Contributing-code">1.1 Contributing code</a></li>
</ul></li>
<li><a id="toc-Coding-Rules-1" href="#Coding-Rules-1">2 Coding Rules</a>
<ul class="no-bullet">
<li><a id="toc-Code-formatting-conventions" href="#Code-formatting-conventions">2.1 Code formatting conventions</a></li>
<li><a id="toc-Comments" href="#Comments">2.2 Comments</a></li>
<li><a id="toc-C-language-features" href="#C-language-features">2.3 C language features</a></li>
<li><a id="toc-Naming-conventions" href="#Naming-conventions">2.4 Naming conventions</a></li>
<li><a id="toc-Miscellaneous-conventions" href="#Miscellaneous-conventions">2.5 Miscellaneous conventions</a></li>
<li><a id="toc-Editor-configuration" href="#Editor-configuration">2.6 Editor configuration</a></li>
</ul></li>
<li><a id="toc-Development-Policy-1" href="#Development-Policy-1">3 Development Policy</a>
<ul class="no-bullet">
<li><a id="toc-Patches_002fCommitting" href="#Patches_002fCommitting">3.1 Patches/Committing</a></li>
<li><a id="toc-Code" href="#Code">3.2 Code</a></li>
<li><a id="toc-Documentation_002fOther" href="#Documentation_002fOther">3.3 Documentation/Other</a></li>
</ul></li>
<li><a id="toc-Code-of-conduct" href="#Code-of-conduct">4 Code of conduct</a></li>
<li><a id="toc-Submitting-patches-1" href="#Submitting-patches-1">5 Submitting patches</a></li>
<li><a id="toc-New-codecs-or-formats-checklist" href="#New-codecs-or-formats-checklist">6 New codecs or formats checklist</a></li>
<li><a id="toc-Patch-submission-checklist" href="#Patch-submission-checklist">7 Patch submission checklist</a></li>
<li><a id="toc-Patch-review-process" href="#Patch-review-process">8 Patch review process</a></li>
<li><a id="toc-Regression-tests-1" href="#Regression-tests-1">9 Regression tests</a>
<ul class="no-bullet">
<li><a id="toc-Adding-files-to-the-fate_002dsuite-dataset" href="#Adding-files-to-the-fate_002dsuite-dataset">9.1 Adding files to the fate-suite dataset</a></li>
<li><a id="toc-Visualizing-Test-Coverage" href="#Visualizing-Test-Coverage">9.2 Visualizing Test Coverage</a></li>
<li><a id="toc-Using-Valgrind" href="#Using-Valgrind">9.3 Using Valgrind</a></li>
</ul></li>
<li><a id="toc-Release-process-1" href="#Release-process-1">10 Release process</a>
<ul class="no-bullet">
<li><a id="toc-Criteria-for-Point-Releases-1" href="#Criteria-for-Point-Releases-1">10.1 Criteria for Point Releases</a></li>
<li><a id="toc-Release-Checklist" href="#Release-Checklist">10.2 Release Checklist</a></li>
</ul></li>
</ul>
</div>
</div>
<a name="Introduction"></a>
<h2 class="chapter">1 Introduction<span class="pull-right"><a class="anchor hidden-xs" href="#Introduction" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Introduction" aria-hidden="true">TOC</a></span></h2>
<p>This text is concerned with the development <em>of</em> FFmpeg itself. Information
on using the FFmpeg libraries in other programs can be found elsewhere, e.g. in:
</p><ul>
<li> the installed header files
</li><li> <a href="http://ffmpeg.org/doxygen/trunk/index.html">the Doxygen documentation</a>
generated from the headers
</li><li> the examples under <samp>doc/examples</samp>
</li></ul>
<p>If you modify FFmpeg code for your own use case, you are highly encouraged to
<em>submit your changes back to us</em>, using this document as a guide. There are
both pragmatic and ideological reasons to do so:
</p><ul>
<li> Maintaining external changes to keep up with upstream development is
time-consuming and error-prone. With your code in the main tree, it will be
maintained by FFmpeg developers.
</li><li> FFmpeg developers include leading experts in the field who can find bugs or
design flaws in your code.
</li><li> By supporting the project you find useful you ensure it continues to be
maintained and developed.
</li></ul>
<p>For more detailed legal information about the use of FFmpeg in
external programs read the <samp>LICENSE</samp> file in the source tree and
consult <a href="https://ffmpeg.org/legal.html">https://ffmpeg.org/legal.html</a>.
</p>
<a name="Contributing-code"></a>
<h3 class="section">1.1 Contributing code<span class="pull-right"><a class="anchor hidden-xs" href="#Contributing-code" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Contributing-code" aria-hidden="true">TOC</a></span></h3>
<p>All proposed code changes should be submitted for review to
<a href="mailto:ffmpeg-devel@ffmpeg.org">the development mailing list</a>, as
described in more detail in the <a href="#Submitting-patches">Submitting patches</a> chapter. The code
should comply with the <a href="#Development-Policy">Development Policy</a> and follow the <a href="#Coding-Rules">Coding Rules</a>.
The developer making the commit and the author are responsible for their changes
and should try to fix issues their commit causes.
</p>
<span id="Coding-Rules"></span><a name="Coding-Rules-1"></a>
<h2 class="chapter">2 Coding Rules<span class="pull-right"><a class="anchor hidden-xs" href="#Coding-Rules-1" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Coding-Rules-1" aria-hidden="true">TOC</a></span></h2>
<a name="Code-formatting-conventions"></a>
<h3 class="section">2.1 Code formatting conventions<span class="pull-right"><a class="anchor hidden-xs" href="#Code-formatting-conventions" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Code-formatting-conventions" aria-hidden="true">TOC</a></span></h3>
<p>There are the following guidelines regarding the indentation in files:
</p>
<ul>
<li> Indent size is 4.
</li><li> 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.
</li><li> You should try to limit your code lines to 80 characters; however, do so if
and only if this improves readability.
</li><li> K&R coding style is used.
</li></ul>
<p>The presentation is one inspired by ’indent -i4 -kr -nut’.
</p>
<p>The main priority in FFmpeg is simplicity and small code size in order to
minimize the bug count.
</p>
<a name="Comments"></a>
<h3 class="section">2.2 Comments<span class="pull-right"><a class="anchor hidden-xs" href="#Comments" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Comments" aria-hidden="true">TOC</a></span></h3>
<p>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.
</p>
<p>Avoid Qt-style and similar Doxygen syntax with <code>!</code> in it, i.e. replace
<code>//!</code> with <code>///</code> and similar. Also @ syntax should be employed
for markup commands, i.e. use <code>@param</code> and not <code>\param</code>.
</p>
<div class="example">
<pre class="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)
...
</pre></div>
<a name="C-language-features"></a>
<h3 class="section">2.3 C language features<span class="pull-right"><a class="anchor hidden-xs" href="#C-language-features" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-C-language-features" aria-hidden="true">TOC</a></span></h3>
<p>FFmpeg is programmed in the ISO C90 language with a few additional
features from ISO C99, namely:
</p>
<ul>
<li> the ‘<samp>inline</samp>’ keyword;
</li><li> ‘<samp>//</samp>’ comments;
</li><li> designated struct initializers (‘<samp>struct s x = { .i = 17 };</samp>’);
</li><li> compound literals (‘<samp>x = (struct s) { 17, 23 };</samp>’).
</li><li> for loops with variable definition (‘<samp>for (int i = 0; i < 8; i++)</samp>’);
</li><li> Variadic macros (‘<samp>#define ARRAY(nb, ...) (int[nb + 1]){ nb, __VA_ARGS__ }</samp>’);
</li><li> Implementation defined behavior for signed integers is assumed to match the
expected behavior for two’s complement. Non representable values in integer
casts are binary truncated. Shift right of signed values uses sign extension.
</li></ul>
<p>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.
</p>
<p>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:
</p>
<ul>
<li> mixing statements and declarations;
</li><li> ‘<samp>long long</samp>’ (use ‘<samp>int64_t</samp>’ instead);
</li><li> ‘<samp>__attribute__</samp>’ not protected by ‘<samp>#ifdef __GNUC__</samp>’ or similar;
</li><li> GCC statement expressions (‘<samp>(x = ({ int y = 4; y; })</samp>’).
</li></ul>
<a name="Naming-conventions"></a>
<h3 class="section">2.4 Naming conventions<span class="pull-right"><a class="anchor hidden-xs" href="#Naming-conventions" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Naming-conventions" aria-hidden="true">TOC</a></span></h3>
<p>All names should be composed with underscores (_), not CamelCase. For example,
‘<samp>avfilter_get_video_buffer</samp>’ is an acceptable function name and
‘<samp>AVFilterGetVideo</samp>’ is not. The exception from this are type names, like
for example structs and enums; they should always be in CamelCase.
</p>
<p>There are the following conventions for naming variables and functions:
</p>
<ul>
<li> For local variables no prefix is required.
</li><li> For file-scope variables and functions declared as <code>static</code>, no prefix
is required.
</li><li> For variables and functions visible outside of file scope, but only used
internally by a library, an <code>ff_</code> prefix should be used,
e.g. ‘<samp>ff_w64_demuxer</samp>’.
</li><li> For variables and functions visible outside of file scope, used internally
across multiple libraries, use <code>avpriv_</code> as prefix, for example,
‘<samp>avpriv_report_missing_feature</samp>’.
</li><li> Each library has its own prefix for public symbols, in addition to the
commonly used <code>av_</code> (<code>avformat_</code> for libavformat,
<code>avcodec_</code> for libavcodec, <code>swr_</code> 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</code> files.
</li></ul>
<p>Furthermore, name space reserved for the system should not be invaded.
Identifiers ending in <code>_t</code> are reserved by
<a href="http://pubs.opengroup.org/onlinepubs/007904975/functions/xsh_chap02_02.html#tag_02_02_02">POSIX</a>.
Also avoid names starting with <code>__</code> or <code>_</code> followed by an uppercase
letter as they are reserved by the C standard. Names starting with <code>_</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>_</code> altogether.
</p>
<a name="Miscellaneous-conventions"></a>
<h3 class="section">2.5 Miscellaneous conventions<span class="pull-right"><a class="anchor hidden-xs" href="#Miscellaneous-conventions" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Miscellaneous-conventions" aria-hidden="true">TOC</a></span></h3>
<ul>
<li> fprintf and printf are forbidden in libavformat and libavcodec,
please use av_log() instead.
</li><li> Casts should be used only when necessary. Unneeded parentheses
should also be avoided if they don’t make the code easier to understand.
</li></ul>
<a name="Editor-configuration"></a>
<h3 class="section">2.6 Editor configuration<span class="pull-right"><a class="anchor hidden-xs" href="#Editor-configuration" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Editor-configuration" aria-hidden="true">TOC</a></span></h3>
<p>In order to configure Vim to follow FFmpeg formatting conventions, paste
the following snippet into your <samp>.vimrc</samp>:
</p><div class="example">
<pre class="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\+$\|\t/
" Do not highlight spaces at the end of line while typing on that line.
autocmd InsertEnter * match ForbiddenWhitespace /\t\|\s\+\%#\@<!$/
</pre></div>
<p>For Emacs, add these roughly equivalent lines to your <samp>.emacs.d/init.el</samp>:
</p><div class="example lisp">
<pre class="lisp">(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")
</pre></div>
<span id="Development-Policy"></span><a name="Development-Policy-1"></a>
<h2 class="chapter">3 Development Policy<span class="pull-right"><a class="anchor hidden-xs" href="#Development-Policy-1" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Development-Policy-1" aria-hidden="true">TOC</a></span></h2>
<a name="Patches_002fCommitting"></a>
<h3 class="section">3.1 Patches/Committing<span class="pull-right"><a class="anchor hidden-xs" href="#Patches_002fCommitting" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Patches_002fCommitting" aria-hidden="true">TOC</a></span></h3>
<a name="Licenses-for-patches-must-be-compatible-with-FFmpeg_002e"></a>
<p>Contributions should be licensed under the
<a href="http://www.gnu.org/licenses/lgpl-2.1.html">LGPL 2.1</a>,
including an "or any later version" clause, or, if you prefer
a gift-style license, the
<a href="http://opensource.org/licenses/isc-license.txt">ISC</a> or
<a href="http://mit-license.org/">MIT</a> license.
<a href="http://www.gnu.org/licenses/gpl-2.0.html">GPL 2</a> including
an "or any later version" clause is also acceptable, but LGPL is
preferred.
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.
</p>
<a name="You-must-not-commit-code-which-breaks-FFmpeg_0021"></a>
<p>This means unfinished code which is enabled and breaks compilation,
or compiles but does not work/breaks the regression tests. Code which
is unfinished but disabled may be permitted under-circumstances, like
missing samples or an implementation with a small subset of features.
Always check the mailing list for any reviewers with issues and test
FATE before you push.
</p>
<a name="Keep-the-main-commit-message-short-with-an-extended-description-below_002e"></a>
<p>The commit message should have a short first line in the form of
a ‘<samp>topic: short description</samp>’ 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.
</p>
<a name="Testing-must-be-adequate-but-not-excessive_002e"></a>
<p>If it works for you, others, and passes FATE then it should be OK to commit
it, provided it fits the other committing criteria. You should not worry about
over-testing things. If your code has problems (portability, triggers
compiler bugs, unusual environment etc) they will be reported and eventually
fixed.
</p>
<a name="Do-not-commit-unrelated-changes-together_002e"></a>
<p>They should be 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.
</p>
<a name="Ask-before-you-change-the-build-system-_0028configure_002c-etc_0029_002e"></a>
<p>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.
</p>
<a name="Cosmetic-changes-should-be-kept-in-separate-patches_002e"></a>
<p>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.
</p>
<p>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
</p>
<a name="Commit-messages-should-always-be-filled-out-properly_002e"></a>
<p>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:
</p>
<div class="example">
<pre class="example">area changed: Short 1 line description
details describing what and why and giving references.
</pre></div>
<a name="Credit-the-author-of-the-patch_002e"></a>
<p>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.
</p>
<a name="Complex-patches-should-refer-to-discussion-surrounding-them_002e"></a>
<p>When applying patches that have been discussed (at length) on the mailing
list, reference the thread in the log message.
</p>
<a name="Always-wait-long-enough-before-pushing-changes"></a>
<p>Do NOT commit to code actively maintained by others without permission.
Send a patch to ffmpeg-devel. If no one answers within a reasonable
time-frame (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!
</p>
<a name="Code"></a>
<h3 class="section">3.2 Code<span class="pull-right"><a class="anchor hidden-xs" href="#Code" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Code" aria-hidden="true">TOC</a></span></h3>
<a name="API_002fABI-changes-should-be-discussed-before-they-are-made_002e"></a>
<p>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 widely used functionality or features (redundant code can be removed).
</p>
<a name="Remember-to-check-if-you-need-to-bump-versions-for-libav_002a_002e"></a>
<p>Depending on the change, you may 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.
</p>
<a name="Warnings-for-correct-code-may-be-disabled-if-there-is-no-other-option_002e"></a>
<p>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.
</p>
<a name="Check-untrusted-input-properly_002e"></a>
<p>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.
</p>
<a name="Documentation_002fOther"></a>
<h3 class="section">3.3 Documentation/Other<span class="pull-right"><a class="anchor hidden-xs" href="#Documentation_002fOther" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Documentation_002fOther" aria-hidden="true">TOC</a></span></h3>
<a name="Subscribe-to-the-ffmpeg_002ddevel-mailing-list_002e"></a>
<p>It is important to be subscribed to the
<a href="https://lists.ffmpeg.org/mailman/listinfo/ffmpeg-devel">ffmpeg-devel</a>
mailing list. Almost any non-trivial patch is to be sent there for review.
Other developers may have comments about your contribution. We expect you see
those comments, and to improve it if requested. (N.B. Experienced committers
have other channels, and may sometimes skip review for trivial fixes.) Also,
discussion here about bug fixes and FFmpeg improvements by other developers may
be helpful information for you. Finally, by being a list subscriber, your
contribution will be posted immediately to the list, without the moderation
hold which messages from non-subscribers experience.
</p>
<p>However, it is more important to the project that we receive your patch than
that you be subscribed to the ffmpeg-devel list. If you have a patch, and don’t
want to subscribe and discuss the patch, then please do send it to the list
anyway.
</p>
<a name="Subscribe-to-the-ffmpeg_002dcvslog-mailing-list_002e"></a>
<p>Diffs of all commits are sent to the
<a href="https://lists.ffmpeg.org/mailman/listinfo/ffmpeg-cvslog">ffmpeg-cvslog</a>
mailing list. Some developers read this list to review all code base changes
from all sources. Subscribing to this list is not mandatory.
</p>
<a name="Keep-the-documentation-up-to-date_002e"></a>
<p>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.
</p>
<a name="Important-discussions-should-be-accessible-to-all_002e"></a>
<p>Try to keep important discussions and requests (also) on the public
developer mailing list, so that all developers can benefit from them.
</p>
<a name="Check-your-entries-in-MAINTAINERS_002e"></a>
<p>Make sure that no parts of the codebase that you maintain are missing from the
<samp>MAINTAINERS</samp> file. If something that you want to maintain is missing add it with
your name after it.
If at some point you no longer want to maintain some code, then please help in
finding a new maintainer and also don’t forget to update the <samp>MAINTAINERS</samp> file.
</p>
<p>We think our rules are not too hard. If you have comments, contact us.
</p>
<a name="Code-of-conduct"></a>
<h2 class="chapter">4 Code of conduct<span class="pull-right"><a class="anchor hidden-xs" href="#Code-of-conduct" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Code-of-conduct" aria-hidden="true">TOC</a></span></h2>
<p>Be friendly and respectful towards others and third parties.
Treat others the way you yourself want to be treated.
</p>
<p>Be considerate. Not everyone shares the same viewpoint and priorities as you do.
Different opinions and interpretations help the project.
Looking at issues from a different perspective assists development.
</p>
<p>Do not assume malice for things that can be attributed to incompetence. Even if
it is malice, it’s rarely good to start with that as initial assumption.
</p>
<p>Stay friendly even if someone acts contrarily. Everyone has a bad day
once in a while.
If you yourself have a bad day or are angry then try to take a break and reply
once you are calm and without anger if you have to.
</p>
<p>Try to help other team members and cooperate if you can.
</p>
<p>The goal of software development is to create technical excellence, not for any
individual to be better and "win" against the others. Large software projects
are only possible and successful through teamwork.
</p>
<p>If someone struggles do not put them down. Give them a helping hand
instead and point them in the right direction.
</p>
<p>Finally, keep in mind the immortal words of Bill and Ted,
"Be excellent to each other."
</p>
<span id="Submitting-patches"></span><a name="Submitting-patches-1"></a>
<h2 class="chapter">5 Submitting patches<span class="pull-right"><a class="anchor hidden-xs" href="#Submitting-patches-1" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Submitting-patches-1" aria-hidden="true">TOC</a></span></h2>
<p>First, read the <a href="#Coding-Rules">Coding Rules</a> above if you did not yet, in particular
the rules regarding patch submission.
</p>
<p>When you submit your patch, please use <code>git format-patch</code> or
<code>git send-email</code>. We cannot read other diffs :-).
</p>
<p>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.
</p>
<p>Use the patcheck tool of FFmpeg to check your patch.
The tool is located in the tools directory.
</p>
<p>Run the <a href="#Regression-tests">Regression tests</a> before submitting a patch in order to verify
it does not cause unexpected problems.
</p>
<p>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()’)
</p>
<p>Also please if you send several patches, send each patch as a separate mail,
do not attach several unrelated patches to the same mail.
</p>
<p>Patches should be posted to the
<a href="https://lists.ffmpeg.org/mailman/listinfo/ffmpeg-devel">ffmpeg-devel</a>
mailing list. Use <code>git send-email</code> 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. Also ensure the correct mime type is used
(text/x-diff or text/x-patch or at least text/plain) and that only one
patch is inline or attached per mail.
You can check <a href="https://patchwork.ffmpeg.org">https://patchwork.ffmpeg.org</a>, if your patch does not show up, its mime type
likely was wrong.
</p>
<a name="Sending-patches-from-email-clients"></a>
<p>Using <code>git send-email</code> might not be desirable for everyone. The
following trick allows to send patches via email clients in a safe
way. It has been tested with Outlook and Thunderbird (with X-Unsent
extension) and might work with other applications.
</p>
<p>Create your patch like this:
</p>
<pre class="verbatim">git format-patch -s -o "outputfolder" --add-header "X-Unsent: 1" --suffix .eml --to ffmpeg-devel@ffmpeg.org -1 1a2b3c4d
</pre>
<p>Now you’ll just need to open the eml file with the email application
and execute ’Send’.
</p>
<a name="Reviews"></a>
<p>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.
</p>
<p>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.
</p>
<a name="New-codecs-or-formats-checklist"></a>
<h2 class="chapter">6 New codecs or formats checklist<span class="pull-right"><a class="anchor hidden-xs" href="#New-codecs-or-formats-checklist" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-New-codecs-or-formats-checklist" aria-hidden="true">TOC</a></span></h2>
<ol>
<li> Did you use av_cold for codec initialization and close functions?
</li><li> Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
AVInputFormat/AVOutputFormat struct?
</li><li> Did you bump the minor version number (and reset the micro version
number) in <samp>libavcodec/version.h</samp> or <samp>libavformat/version.h</samp>?
</li><li> Did you register it in <samp>allcodecs.c</samp> or <samp>allformats.c</samp>?
</li><li> Did you add the AVCodecID to <samp>avcodec.h</samp>?
When adding new codec IDs, also add an entry to the codec descriptor
list in <samp>libavcodec/codec_desc.c</samp>.
</li><li> If it has a FourCC, did you add it to <samp>libavformat/riff.c</samp>,
even if it is only a decoder?
</li><li> 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.
</li><li> Did you add an entry to the table of supported formats or codecs in
<samp>doc/general.texi</samp>?
</li><li> Did you add an entry in the Changelog?
</li><li> If it depends on a parser or a library, did you add that dependency in
configure?
</li><li> Did you <code>git add</code> the appropriate files before committing?
</li><li> Did you make sure it compiles standalone, i.e. with
<code>configure --disable-everything --enable-decoder=foo</code>
(or <code>--enable-demuxer</code> or whatever your component is)?
</li></ol>
<a name="Patch-submission-checklist"></a>
<h2 class="chapter">7 Patch submission checklist<span class="pull-right"><a class="anchor hidden-xs" href="#Patch-submission-checklist" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Patch-submission-checklist" aria-hidden="true">TOC</a></span></h2>
<ol>
<li> Does <code>make fate</code> pass with the patch applied?
</li><li> Was the patch generated with git format-patch or send-email?
</li><li> Did you sign-off your patch? (<code>git commit -s</code>)
See <a href="https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/plain/Documentation/process/submitting-patches.rst">Sign your work</a> for the meaning
of <em>sign-off</em>.
</li><li> Did you provide a clear git commit log message?
</li><li> Is the patch against latest FFmpeg git master branch?
</li><li> Are you subscribed to ffmpeg-devel?
(the list is subscribers only due to spam)
</li><li> Have you checked that the changes are minimal, so that the same cannot be
achieved with a smaller patch and/or simpler final code?
</li><li> If the change is to speed critical code, did you benchmark it?
</li><li> If you did any benchmarks, did you provide them in the mail?
</li><li> Have you checked that the patch does not introduce buffer overflows or
other security issues?
</li><li> Did you test your decoder or demuxer against damaged data? If no, see
tools/trasher, the noise bitstream filter, and
<a href="http://caca.zoy.org/wiki/zzuf">zzuf</a>. Your decoder or demuxer
should not crash, end in a (near) infinite loop, or allocate ridiculous
amounts of memory when fed damaged data.
</li><li> Did you test your decoder or demuxer against sample files?
Samples may be obtained at <a href="https://samples.ffmpeg.org">https://samples.ffmpeg.org</a>.
</li><li> Does the patch not mix functional and cosmetic changes?
</li><li> Did you add tabs or trailing whitespace to the code? Both are forbidden.
</li><li> Is the patch attached to the email you send?
</li><li> 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.
</li><li> If the patch fixes a bug, did you provide a verbose analysis of the bug?
</li><li> 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 <a href="https://streams.videolan.org/upload/">https://streams.videolan.org/upload/</a>.
</li><li> Did you provide a verbose summary about what the patch does change?
</li><li> Did you provide a verbose explanation why it changes things like it does?
</li><li> Did you provide a verbose summary of the user visible advantages and
disadvantages if the patch is applied?
</li><li> Did you provide an example so we can verify the new feature added by the
patch easily?
</li><li> 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.
</li><li> You should maintain alphabetical order in alphabetically ordered lists as
long as doing so does not break API/ABI compatibility.
</li><li> Lines with similar content should be aligned vertically when doing so
improves readability.
</li><li> Consider adding a regression test for your code.
</li><li> If you added YASM code please check that things still work with –disable-yasm.
</li><li> Make sure you check the return values of function and return appropriate
error codes. Especially memory allocation functions like <code>av_malloc()</code>
are notoriously left unchecked, which is a serious problem.
</li><li> Test your code with valgrind and or Address Sanitizer to ensure it’s free
of leaks, out of array accesses, etc.
</li></ol>
<a name="Patch-review-process"></a>
<h2 class="chapter">8 Patch review process<span class="pull-right"><a class="anchor hidden-xs" href="#Patch-review-process" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Patch-review-process" aria-hidden="true">TOC</a></span></h2>
<p>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.
</p>
<p>We will review all submitted patches, but sometimes we are quite busy so
especially for large patches this can take several weeks.
</p>
<p>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.
</p>
<p>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.
</p>
<p>Everyone is welcome to review patches. Also if you are waiting for your patch
to be reviewed, please consider helping to review other patches, that is a great
way to get everyone’s patches reviewed sooner.
</p>
<span id="Regression-tests"></span><a name="Regression-tests-1"></a>
<h2 class="chapter">9 Regression tests<span class="pull-right"><a class="anchor hidden-xs" href="#Regression-tests-1" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Regression-tests-1" aria-hidden="true">TOC</a></span></h2>
<p>Before submitting a patch (or committing to the repository), you should at least
test that you did not break anything.
</p>
<p>Running ’make fate’ accomplishes this, please see <a href="fate.html">fate.html</a> for details.
</p>
<p>[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].
</p>
<a name="Adding-files-to-the-fate_002dsuite-dataset"></a>
<h3 class="section">9.1 Adding files to the fate-suite dataset<span class="pull-right"><a class="anchor hidden-xs" href="#Adding-files-to-the-fate_002dsuite-dataset" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Adding-files-to-the-fate_002dsuite-dataset" aria-hidden="true">TOC</a></span></h3>
<p>When there is no muxer or encoder available to generate test media for a
specific test then the media has to be included 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 introductory message for the patch series that you post to
the ffmpeg-devel mailing list, a direct link to download the sample media.
</p>
<a name="Visualizing-Test-Coverage"></a>
<h3 class="section">9.2 Visualizing Test Coverage<span class="pull-right"><a class="anchor hidden-xs" href="#Visualizing-Test-Coverage" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Visualizing-Test-Coverage" aria-hidden="true">TOC</a></span></h3>
<p>The FFmpeg build system allows visualizing the test coverage in an easy
manner with the coverage tools <code>gcov</code>/<code>lcov</code>. This involves
the following steps:
</p>
<ol>
<li> Configure to compile with instrumentation enabled:
<code>configure --toolchain=gcov</code>.
</li><li> 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 FFmpeg, in any combination.
</li><li> Run <code>make lcov</code> to generate coverage data in HTML format.
</li><li> View <code>lcov/index.html</code> in your preferred HTML viewer.
</li></ol>
<p>You can use the command <code>make lcov-reset</code> to reset the coverage
measurements. You will need to rerun <code>make lcov</code> after running a
new test.
</p>
<a name="Using-Valgrind"></a>
<h3 class="section">9.3 Using Valgrind<span class="pull-right"><a class="anchor hidden-xs" href="#Using-Valgrind" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Using-Valgrind" aria-hidden="true">TOC</a></span></h3>
<p>The configure script provides a shortcut for using valgrind to spot bugs
related to memory handling. Just add the option
<code>--toolchain=valgrind-memcheck</code> or <code>--toolchain=valgrind-massif</code>
to your configure line, and reasonable defaults will be set for running
FATE under the supervision of either the <strong>memcheck</strong> or the
<strong>massif</strong> tool of the valgrind suite.
</p>
<p>In case you need finer control over how valgrind is invoked, use the
<code>--target-exec='valgrind <your_custom_valgrind_options></code> option in
your configure line instead.
</p>
<span id="Release-process"></span><a name="Release-process-1"></a>
<h2 class="chapter">10 Release process<span class="pull-right"><a class="anchor hidden-xs" href="#Release-process-1" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Release-process-1" aria-hidden="true">TOC</a></span></h2>
<p>FFmpeg maintains a set of <strong>release branches</strong>, which are the
recommended deliverable for system integrators and distributors (such as
Linux distributions, etc.). At regular times, a <strong>release
manager</strong> prepares, tests and publishes tarballs on the
<a href="https://ffmpeg.org">https://ffmpeg.org</a> website.
</p>
<p>There are two kinds of releases:
</p>
<ol>
<li> <strong>Major releases</strong> always include the latest and greatest
features and functionality.
</li><li> <strong>Point releases</strong> are cut from <strong>release</strong> branches,
which are named <code>release/X</code>, with <code>X</code> being the release
version number.
</li></ol>
<p>Note that we promise to our users that shared libraries from any FFmpeg
release never break programs that have been <strong>compiled</strong> against
previous versions of <strong>the same release series</strong> in any case!
</p>
<p>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</strong> mailing list in time to allow forward planning.
</p>
<span id="Criteria-for-Point-Releases"></span><a name="Criteria-for-Point-Releases-1"></a>
<h3 class="section">10.1 Criteria for Point Releases<span class="pull-right"><a class="anchor hidden-xs" href="#Criteria-for-Point-Releases-1" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Criteria-for-Point-Releases-1" aria-hidden="true">TOC</a></span></h3>
<p>Changes that match the following criteria are valid candidates for
inclusion into a point release:
</p>
<ol>
<li> Fixes a security issue, preferably identified by a <strong>CVE
number</strong> issued by <a href="http://cve.mitre.org/">http://cve.mitre.org/</a>.
</li><li> Fixes a documented bug in <a href="https://trac.ffmpeg.org">https://trac.ffmpeg.org</a>.
</li><li> Improves the included documentation.
</li><li> Retains both source code and binary compatibility with previous
point releases of the same release branch.
</li></ol>
<p>The order for checking the rules is (1 OR 2 OR 3) AND 4.
</p>
<a name="Release-Checklist"></a>
<h3 class="section">10.2 Release Checklist<span class="pull-right"><a class="anchor hidden-xs" href="#Release-Checklist" aria-hidden="true">#</a> <a class="anchor hidden-xs"href="#toc-Release-Checklist" aria-hidden="true">TOC</a></span></h3>
<p>The release process involves the following steps:
</p>
<ol>
<li> Ensure that the <samp>RELEASE</samp> file contains the version number for
the upcoming release.
</li><li> Add the release at <a href="https://trac.ffmpeg.org/admin/ticket/versions">https://trac.ffmpeg.org/admin/ticket/versions</a>.
</li><li> Announce the intent to do a release to the mailing list.
</li><li> Make sure all relevant security fixes have been backported. See
<a href="https://ffmpeg.org/security.html">https://ffmpeg.org/security.html</a>.
</li><li> Ensure that the FATE regression suite still passes in the release
branch on at least <strong>i386</strong> and <strong>amd64</strong>
(cf. <a href="#Regression-tests">Regression tests</a>).
</li><li> Prepare the release tarballs in <code>bz2</code> and <code>gz</code> formats, and
supplementing files that contain <code>gpg</code> signatures
</li><li> Publish the tarballs at <a href="https://ffmpeg.org/releases">https://ffmpeg.org/releases</a>. Create and
push an annotated tag in the form <code>nX</code>, with <code>X</code>
containing the version number.
</li><li> Propose and send a patch to the <strong>ffmpeg-devel</strong> mailing list
with a news entry for the website.
</li><li> Publish the news entry.
</li><li> Send an announcement to the mailing list.
</li></ol>
<p style="font-size: small;">
This document was generated using <a href="https://www.gnu.org/software/texinfo/"><em>makeinfo</em></a>.
</p>
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