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Explicitly document our usage of assembly, following suit with other architectures. Signed-off-by: J. Dekker <jdek@itanimul.li>
1029 lines
40 KiB
Plaintext
1029 lines
40 KiB
Plaintext
\input texinfo @c -*- texinfo -*-
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@documentencoding UTF-8
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@settitle Developer Documentation
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@titlepage
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@center @titlefont{Developer Documentation}
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@end titlepage
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@top
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@contents
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@chapter Introduction
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This text is concerned with the development @emph{of} FFmpeg itself. Information
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on using the FFmpeg libraries in other programs can be found elsewhere, e.g. in:
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@itemize @bullet
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@item
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the installed header files
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@item
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@url{http://ffmpeg.org/doxygen/trunk/index.html, the Doxygen documentation}
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generated from the headers
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@item
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the examples under @file{doc/examples}
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@end itemize
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For more detailed legal information about the use of FFmpeg in
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external programs read the @file{LICENSE} file in the source tree and
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consult @url{https://ffmpeg.org/legal.html}.
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If you modify FFmpeg code for your own use case, you are highly encouraged to
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@emph{submit your changes back to us}, using this document as a guide. There are
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both pragmatic and ideological reasons to do so:
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@itemize @bullet
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@item
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Maintaining external changes to keep up with upstream development is
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time-consuming and error-prone. With your code in the main tree, it will be
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maintained by FFmpeg developers.
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@item
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FFmpeg developers include leading experts in the field who can find bugs or
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design flaws in your code.
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@item
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By supporting the project you find useful you ensure it continues to be
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maintained and developed.
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@end itemize
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All proposed code changes should be submitted for review to
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@url{mailto:ffmpeg-devel@@ffmpeg.org, the development mailing list}, as
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described in more detail in the @ref{Submitting patches} chapter. The code
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should comply with the @ref{Development Policy} and follow the @ref{Coding Rules}.
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The developer making the commit and the author are responsible for their changes
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and should try to fix issues their commit causes.
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@anchor{Coding Rules}
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@chapter Coding Rules
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@section Language
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FFmpeg is mainly programmed in the ISO C99 language, extended with:
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@itemize @bullet
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@item
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Atomic operations from C11 @file{stdatomic.h}. They are emulated on
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architectures/compilers that do not support them, so all FFmpeg-internal code
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may use atomics without any extra checks. However, @file{stdatomic.h} must not
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be included in public headers, so they stay C99-compatible.
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@end itemize
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Compiler-specific extensions may be used with good reason, but must not be
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depended on, i.e. the code must still compile and work with compilers lacking
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the extension.
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The following C99 features must not be used anywhere in the codebase:
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@itemize @bullet
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@item
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variable-length arrays;
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@item
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complex numbers;
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@item
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mixed statements and declarations.
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@end itemize
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@subsection SIMD/DSP
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@anchor{SIMD/DSP}
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As modern compilers are unable to generate efficient SIMD or other
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performance-critical DSP code from plain C, handwritten assembly is used.
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Usually such code is isolated in a separate function. Then the standard approach
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is writing multiple versions of this function – a plain C one that works
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everywhere and may also be useful for debugging, and potentially multiple
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architecture-specific optimized implementations. Initialization code then
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chooses the best available version at runtime and loads it into a function
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pointer; the function in question is then always called through this pointer.
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The specific syntax used for writing assembly is:
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@itemize @bullet
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@item
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NASM on x86;
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@item
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GAS on ARM and RISC-V.
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@end itemize
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A unit testing framework for assembly called @code{checkasm} lives under
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@file{tests/checkasm}. All new assembly should come with @code{checkasm} tests;
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adding tests for existing assembly that lacks them is also strongly encouraged.
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@subsection Other languages
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Other languages than C may be used in special cases:
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@itemize @bullet
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@item
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Compiler intrinsics or inline assembly when the code in question cannot be
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written in the standard way described in the @ref{SIMD/DSP} section. This
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typically applies to code that needs to be inlined.
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@item
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Objective-C where required for interacting with macOS-specific interfaces.
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@end itemize
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@section Code formatting conventions
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There are the following guidelines regarding the indentation in files:
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@itemize @bullet
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@item
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Indent size is 4.
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@item
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The TAB character is forbidden outside of Makefiles as is any
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form of trailing whitespace. Commits containing either will be
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rejected by the git repository.
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@item
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You should try to limit your code lines to 80 characters; however, do so if
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and only if this improves readability.
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@item
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K&R coding style is used.
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@end itemize
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The presentation is one inspired by 'indent -i4 -kr -nut'.
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@subsection Vim configuration
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In order to configure Vim to follow FFmpeg formatting conventions, paste
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the following snippet into your @file{.vimrc}:
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@example
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" indentation rules for FFmpeg: 4 spaces, no tabs
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set expandtab
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set shiftwidth=4
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set softtabstop=4
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set cindent
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set cinoptions=(0
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" Allow tabs in Makefiles.
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autocmd FileType make,automake set noexpandtab shiftwidth=8 softtabstop=8
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" Trailing whitespace and tabs are forbidden, so highlight them.
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highlight ForbiddenWhitespace ctermbg=red guibg=red
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match ForbiddenWhitespace /\s\+$\|\t/
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" Do not highlight spaces at the end of line while typing on that line.
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autocmd InsertEnter * match ForbiddenWhitespace /\t\|\s\+\%#\@@<!$/
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@end example
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@subsection Emacs configuration
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For Emacs, add these roughly equivalent lines to your @file{.emacs.d/init.el}:
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@lisp
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(c-add-style "ffmpeg"
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'("k&r"
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(c-basic-offset . 4)
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(indent-tabs-mode . nil)
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(show-trailing-whitespace . t)
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(c-offsets-alist
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(statement-cont . (c-lineup-assignments +)))
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)
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)
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(setq c-default-style "ffmpeg")
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@end lisp
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@section Comments
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Use the JavaDoc/Doxygen format (see examples below) so that code documentation
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can be generated automatically. All nontrivial functions should have a comment
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above them explaining what the function does, even if it is just one sentence.
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All structures and their member variables should be documented, too.
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Avoid Qt-style and similar Doxygen syntax with @code{!} in it, i.e. replace
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@code{//!} with @code{///} and similar. Also @@ syntax should be employed
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for markup commands, i.e. use @code{@@param} and not @code{\param}.
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@example
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/**
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* @@file
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* MPEG codec.
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* @@author ...
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*/
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/**
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* Summary sentence.
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* more text ...
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* ...
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*/
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typedef struct Foobar @{
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int var1; /**< var1 description */
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int var2; ///< var2 description
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/** var3 description */
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int var3;
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@} Foobar;
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/**
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* Summary sentence.
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* more text ...
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* ...
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* @@param my_parameter description of my_parameter
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* @@return return value description
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*/
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int myfunc(int my_parameter)
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...
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@end example
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@anchor{Naming conventions}
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@section Naming conventions
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Names of functions, variables, and struct members must be lowercase, using
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underscores (_) to separate words. For example, @samp{avfilter_get_video_buffer}
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is an acceptable function name and @samp{AVFilterGetVideo} is not.
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Struct, union, enum, and typedeffed type names must use CamelCase. All structs
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and unions should be typedeffed to the same name as the struct/union tag, e.g.
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@code{typedef struct AVFoo @{ ... @} AVFoo;}. Enums are typically not
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typedeffed.
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Enumeration constants and macros must be UPPERCASE, except for macros
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masquerading as functions, which should use the function naming convention.
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All identifiers in the libraries should be namespaced as follows:
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@itemize @bullet
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@item
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No namespacing for identifiers with file and lower scope (e.g. local variables,
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static functions), and struct and union members,
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@item
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The @code{ff_} prefix must be used for variables and functions visible outside
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of file scope, but only used internally within a single library, e.g.
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@samp{ff_w64_demuxer}. This prevents name collisions when FFmpeg is statically
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linked.
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@item
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For variables and functions visible outside of file scope, used internally
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across multiple libraries, use @code{avpriv_} as prefix, for example,
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@samp{avpriv_report_missing_feature}.
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@item
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All other internal identifiers, like private type or macro names, should be
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namespaced only to avoid possible internal conflicts. E.g. @code{H264_NAL_SPS}
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vs. @code{HEVC_NAL_SPS}.
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@item
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Each library has its own prefix for public symbols, in addition to the
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commonly used @code{av_} (@code{avformat_} for libavformat,
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@code{avcodec_} for libavcodec, @code{swr_} for libswresample, etc).
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Check the existing code and choose names accordingly.
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@item
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Other public identifiers (struct, union, enum, macro, type names) must use their
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library's public prefix (@code{AV}, @code{Sws}, or @code{Swr}).
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@end itemize
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Furthermore, name space reserved for the system should not be invaded.
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Identifiers ending in @code{_t} are reserved by
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@url{http://pubs.opengroup.org/onlinepubs/007904975/functions/xsh_chap02_02.html#tag_02_02_02, POSIX}.
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Also avoid names starting with @code{__} or @code{_} followed by an uppercase
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letter as they are reserved by the C standard. Names starting with @code{_}
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are reserved at the file level and may not be used for externally visible
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symbols. If in doubt, just avoid names starting with @code{_} altogether.
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@section Miscellaneous conventions
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@itemize @bullet
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@item
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Casts should be used only when necessary. Unneeded parentheses
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should also be avoided if they don't make the code easier to understand.
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@end itemize
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@anchor{Development Policy}
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@chapter Development Policy
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@section Code behaviour
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@subheading Correctness
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The code must be valid. It must not crash, abort, access invalid pointers, leak
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memory, cause data races or signed integer overflow, or otherwise cause
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undefined behaviour. Error codes should be checked and, when applicable,
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forwarded to the caller.
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@subheading Thread- and library-safety
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Our libraries may be called by multiple independent callers in the same process.
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These calls may happen from any number of threads and the different call sites
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may not be aware of each other - e.g. a user program may be calling our
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libraries directly, and use one or more libraries that also call our libraries.
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The code must behave correctly under such conditions.
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@subheading Robustness
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The code must treat as untrusted any bytestream received from a caller or read
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from a file, network, etc. It must not misbehave when arbitrary data is sent to
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it - typically it should print an error message and return
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@code{AVERROR_INVALIDDATA} on encountering invalid input data.
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@subheading Memory allocation
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The code must use the @code{av_malloc()} family of functions from
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@file{libavutil/mem.h} to perform all memory allocation, except in special cases
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(e.g. when interacting with an external library that requires a specific
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allocator to be used).
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All allocations should be checked and @code{AVERROR(ENOMEM)} returned on
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failure. A common mistake is that error paths leak memory - make sure that does
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not happen.
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@subheading stdio
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Our libraries must not access the stdio streams stdin/stdout/stderr directly
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(e.g. via @code{printf()} family of functions), as that is not library-safe. For
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logging, use @code{av_log()}.
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@section Patches/Committing
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@subheading Licenses for patches must be compatible with FFmpeg.
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Contributions should be licensed under the
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@uref{http://www.gnu.org/licenses/lgpl-2.1.html, LGPL 2.1},
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including an "or any later version" clause, or, if you prefer
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a gift-style license, the
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@uref{http://opensource.org/licenses/isc-license.txt, ISC} or
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@uref{http://mit-license.org/, MIT} license.
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@uref{http://www.gnu.org/licenses/gpl-2.0.html, GPL 2} including
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an "or any later version" clause is also acceptable, but LGPL is
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preferred.
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If you add a new file, give it a proper license header. Do not copy and
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paste it from a random place, use an existing file as template.
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@subheading You must not commit code which breaks FFmpeg!
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This means unfinished code which is enabled and breaks compilation,
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or compiles but does not work/breaks the regression tests. Code which
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is unfinished but disabled may be permitted under-circumstances, like
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missing samples or an implementation with a small subset of features.
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Always check the mailing list for any reviewers with issues and test
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FATE before you push.
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@subheading Commit messages
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Commit messages are highly important tools for informing other developers on
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what a given change does and why. Every commit must always have a properly
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filled out commit message with the following format:
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@example
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area changed: short 1 line description
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details describing what and why and giving references.
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@end example
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If the commit addresses a known bug on our bug tracker or other external issue
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(e.g. CVE), the commit message should include the relevant bug ID(s) or other
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external identifiers. Note that this should be done in addition to a proper
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explanation and not instead of it. Comments such as "fixed!" or "Changed it."
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are not acceptable.
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When applying patches that have been discussed at length on the mailing list,
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reference the thread in the commit message.
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@subheading Testing must be adequate but not excessive.
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If it works for you, others, and passes FATE then it should be OK to commit
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it, provided it fits the other committing criteria. You should not worry about
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over-testing things. If your code has problems (portability, triggers
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compiler bugs, unusual environment etc) they will be reported and eventually
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fixed.
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@subheading Do not commit unrelated changes together.
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They should be split them into self-contained pieces. Also do not forget
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that if part B depends on part A, but A does not depend on B, then A can
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and should be committed first and separate from B. Keeping changes well
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split into self-contained parts makes reviewing and understanding them on
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the commit log mailing list easier. This also helps in case of debugging
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later on.
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Also if you have doubts about splitting or not splitting, do not hesitate to
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ask/discuss it on the developer mailing list.
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@subheading Cosmetic changes should be kept in separate patches.
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We refuse source indentation and other cosmetic changes if they are mixed
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with functional changes, such commits will be rejected and removed. Every
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developer has his own indentation style, you should not change it. Of course
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if you (re)write something, you can use your own style, even though we would
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prefer if the indentation throughout FFmpeg was consistent (Many projects
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force a given indentation style - we do not.). If you really need to make
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indentation changes (try to avoid this), separate them strictly from real
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changes.
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NOTE: If you had to put if()@{ .. @} over a large (> 5 lines) chunk of code,
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then either do NOT change the indentation of the inner part within (do not
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move it to the right)! or do so in a separate commit
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@subheading Credit the author of the patch.
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Make sure the author of the commit is set correctly. (see git commit --author)
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If you apply a patch, send an
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answer to ffmpeg-devel (or wherever you got the patch from) saying that
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you applied the patch.
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@subheading Always wait long enough before pushing changes
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Do NOT commit to code actively maintained by others without permission.
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Send a patch to ffmpeg-devel. If no one answers within a reasonable
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time-frame (12h for build failures and security fixes, 3 days small changes,
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1 week for big patches) then commit your patch if you think it is OK.
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Also note, the maintainer can simply ask for more time to review!
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@section Code
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@subheading Warnings for correct code may be disabled if there is no other option.
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Compiler warnings indicate potential bugs or code with bad style. If a type of
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warning always points to correct and clean code, that warning should
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be disabled, not the code changed.
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Thus the remaining warnings can either be bugs or correct code.
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If it is a bug, the bug has to be fixed. If it is not, the code should
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be changed to not generate a warning unless that causes a slowdown
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or obfuscates the code.
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@section Library public interfaces
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Every library in FFmpeg provides a set of public APIs in its installed headers,
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which are those listed in the variable @code{HEADERS} in that library's
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@file{Makefile}. All identifiers defined in those headers (except for those
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explicitly documented otherwise), and corresponding symbols exported from
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compiled shared or static libraries are considered public interfaces and must
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comply with the API and ABI compatibility rules described in this section.
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Public APIs must be backward compatible within a given major version. I.e. any
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valid user code that compiles and works with a given library version must still
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compile and work with any later version, as long as the major version number is
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unchanged. "Valid user code" here means code that is calling our APIs in a
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documented and/or intended manner and is not relying on any undefined behavior.
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Incrementing the major version may break backward compatibility, but only to the
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extent described in @ref{Major version bumps}.
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We also guarantee backward ABI compatibility for shared and static libraries.
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I.e. it should be possible to replace a shared or static build of our library
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with a build of any later version (re-linking the user binary in the static
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case) without breaking any valid user binaries, as long as the major version
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number remains unchanged.
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@subsection Adding new interfaces
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Any new public identifiers in installed headers are considered new API - this
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includes new functions, structs, macros, enum values, typedefs, new fields in
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existing structs, new installed headers, etc. Consider the following
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guidelines when adding new APIs.
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@subsubheading Motivation
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While new APIs can be added relatively easily, changing or removing them is much
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harder due to abovementioned compatibility requirements. You should then
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consider carefully whether the functionality you are adding really needs to be
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exposed to our callers as new public API.
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Your new API should have at least one well-established use case outside of the
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library that cannot be easily achieved with existing APIs. Every library in
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FFmpeg also has a defined scope - your new API must fit within it.
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@subsubheading Replacing existing APIs
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If your new API is replacing an existing one, it should be strictly superior to
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it, so that the advantages of using the new API outweight the cost to the
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callers of changing their code. After adding the new API you should then
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deprecate the old one and schedule it for removal, as described in
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@ref{Removing interfaces}.
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If you deem an existing API deficient and want to fix it, the preferred approach
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in most cases is to add a differently-named replacement and deprecate the
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existing API rather than modify it. It is important to make the changes visible
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to our callers (e.g. through compile- or run-time deprecation warnings) and make
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it clear how to transition to the new API (e.g. in the Doxygen documentation or
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on the wiki).
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@subsubheading API design
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|
The FFmpeg libraries are used by a variety of callers to perform a wide range of
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multimedia-related processing tasks. You should therefore - within reason - try
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|
to design your new API for the broadest feasible set of use cases and avoid
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unnecessarily limiting it to a specific type of callers (e.g. just media
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playback or just transcoding).
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|
@subsubheading Consistency
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|
Check whether similar APIs already exist in FFmpeg. If they do, try to model
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your new addition on them to achieve better overall consistency.
|
|
|
|
The naming of your new identifiers should follow the @ref{Naming conventions}
|
|
and be aligned with other similar APIs, if applicable.
|
|
|
|
@subsubheading Extensibility
|
|
You should also consider how your API might be extended in the future in a
|
|
backward-compatible way. If you are adding a new struct @code{AVFoo}, the
|
|
standard approach is requiring the caller to always allocate it through a
|
|
constructor function, typically named @code{av_foo_alloc()}. This way new fields
|
|
may be added to the end of the struct without breaking ABI compatibility.
|
|
Typically you will also want a destructor - @code{av_foo_free(AVFoo**)} that
|
|
frees the indirectly supplied object (and its contents, if applicable) and
|
|
writes @code{NULL} to the supplied pointer, thus eliminating the potential
|
|
dangling pointer in the caller's memory.
|
|
|
|
If you are adding new functions, consider whether it might be desirable to tweak
|
|
their behavior in the future - you may want to add a flags argument, even though
|
|
it would be unused initially.
|
|
|
|
@subsubheading Documentation
|
|
All new APIs must be documented as Doxygen-formatted comments above the
|
|
identifiers you add to the public headers. You should also briefly mention the
|
|
change in @file{doc/APIchanges}.
|
|
|
|
@subsubheading Bump the version
|
|
Backward-incompatible API or ABI changes require incrementing (bumping) the
|
|
major version number, as described in @ref{Major version bumps}. Major
|
|
bumps are significant events that happen on a schedule - so if your change
|
|
strictly requires one you should add it under @code{#if} preprocesor guards that
|
|
disable it until the next major bump happens.
|
|
|
|
New APIs that can be added without breaking API or ABI compatibility require
|
|
bumping the minor version number.
|
|
|
|
Incrementing the third (micro) version 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.
|
|
|
|
@anchor{Removing interfaces}
|
|
@subsection Removing interfaces
|
|
Due to abovementioned compatibility guarantees, removing APIs is an involved
|
|
process that should only be undertaken with good reason. Typically a deficient,
|
|
restrictive, or otherwise inadequate API is replaced by a superior one, though
|
|
it does at times happen that we remove an API without any replacement (e.g. when
|
|
the feature it provides is deemed not worth the maintenance effort, out of scope
|
|
of the project, fundamentally flawed, etc.).
|
|
|
|
The removal has two steps - first the API is deprecated and scheduled for
|
|
removal, but remains present and functional. The second step is actually
|
|
removing the API - this is described in @ref{Major version bumps}.
|
|
|
|
To deprecate an API you should signal to our users that they should stop using
|
|
it. E.g. if you intend to remove struct members or functions, you should mark
|
|
them with @code{attribute_deprecated}. When this cannot be done, it may be
|
|
possible to detect the use of the deprecated API at runtime and print a warning
|
|
(though take care not to print it too often). You should also document the
|
|
deprecation (and the replacement, if applicable) in the relevant Doxygen
|
|
documentation block.
|
|
|
|
Finally, you should define a deprecation guard along the lines of
|
|
@code{#define FF_API_<FOO> (LIBAVBAR_VERSION_MAJOR < XX)} (where XX is the major
|
|
version in which the API will be removed) in @file{libavbar/version_major.h}
|
|
(@file{version.h} in case of @code{libavutil}). Then wrap all uses of the
|
|
deprecated API in @code{#if FF_API_<FOO> .... #endif}, so that the code will
|
|
automatically get disabled once the major version reaches XX. You can also use
|
|
@code{FF_DISABLE_DEPRECATION_WARNINGS} and @code{FF_ENABLE_DEPRECATION_WARNINGS}
|
|
to suppress compiler deprecation warnings inside these guards. You should test
|
|
that the code compiles and works with the guard macro evaluating to both true
|
|
and false.
|
|
|
|
@anchor{Major version bumps}
|
|
@subsection Major version bumps
|
|
A major version bump signifies an API and/or ABI compatibility break. To reduce
|
|
the negative effects on our callers, who are required to adapt their code,
|
|
backward-incompatible changes during a major bump should be limited to:
|
|
@itemize @bullet
|
|
@item
|
|
Removing previously deprecated APIs.
|
|
|
|
@item
|
|
Performing ABI- but not API-breaking changes, like reordering struct contents.
|
|
@end itemize
|
|
|
|
@section Documentation/Other
|
|
@subheading Subscribe to the ffmpeg-devel mailing list.
|
|
It is important to be subscribed to the
|
|
@uref{https://lists.ffmpeg.org/mailman/listinfo/ffmpeg-devel, ffmpeg-devel}
|
|
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.
|
|
|
|
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.
|
|
|
|
@subheading Subscribe to the ffmpeg-cvslog mailing list.
|
|
Diffs of all commits are sent to the
|
|
@uref{https://lists.ffmpeg.org/mailman/listinfo/ffmpeg-cvslog, ffmpeg-cvslog}
|
|
mailing list. Some developers read this list to review all code base changes
|
|
from all sources. Subscribing to this list is not mandatory.
|
|
|
|
@subheading Keep the documentation up to date.
|
|
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.
|
|
|
|
@subheading Important discussions should be accessible to all.
|
|
Try to keep important discussions and requests (also) on the public
|
|
developer mailing list, so that all developers can benefit from them.
|
|
|
|
@subheading Check your entries in MAINTAINERS.
|
|
Make sure that no parts of the codebase that you maintain are missing from the
|
|
@file{MAINTAINERS} 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 @file{MAINTAINERS} file.
|
|
|
|
We think our rules are not too hard. If you have comments, contact us.
|
|
|
|
@anchor{Submitting patches}
|
|
@chapter 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{https://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. 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 @url{https://patchwork.ffmpeg.org}, if your patch does not show up, its mime type
|
|
likely was wrong.
|
|
|
|
@subheading Sending patches from email clients
|
|
Using @code{git send-email} 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.
|
|
|
|
Create your patch like this:
|
|
|
|
@verbatim
|
|
git format-patch -s -o "outputfolder" --add-header "X-Unsent: 1" --suffix .eml --to ffmpeg-devel@ffmpeg.org -1 1a2b3c4d
|
|
@end verbatim
|
|
|
|
Now you'll just need to open the eml file with the email application
|
|
and execute 'Send'.
|
|
|
|
@subheading Reviews
|
|
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.
|
|
|
|
|
|
@chapter 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
|
|
|
|
|
|
@chapter 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? (@code{git commit -s})
|
|
See @uref{https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/plain/Documentation/process/submitting-patches.rst, Sign your work} for the meaning
|
|
of @dfn{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
|
|
Did you test your decoder or demuxer against sample files?
|
|
Samples may be obtained at @url{https://samples.ffmpeg.org}.
|
|
|
|
@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 @url{https://streams.videolan.org/upload/}.
|
|
|
|
@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 adding a regression test for your code. All new modules
|
|
should be covered by tests. That includes demuxers, muxers, decoders, encoders
|
|
filters, bitstream filters, parsers. If its not possible to do that, add
|
|
an explanation why to your patchset, its ok to not test if theres a reason.
|
|
|
|
@item
|
|
If you added YASM code please check that things still work with --disable-yasm.
|
|
|
|
@item
|
|
Test your code with valgrind and or Address Sanitizer to ensure it's free
|
|
of leaks, out of array accesses, etc.
|
|
@end enumerate
|
|
|
|
@chapter 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.
|
|
|
|
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.
|
|
|
|
@anchor{Regression tests}
|
|
@chapter 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].
|
|
|
|
@section Adding files to the fate-suite dataset
|
|
|
|
If you need a sample uploaded send a mail to samples-request.
|
|
|
|
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.
|
|
|
|
@section Visualizing Test Coverage
|
|
|
|
The FFmpeg build system allows visualizing the test coverage in an easy
|
|
manner with the coverage tools @code{gcov}/@code{lcov}. This involves
|
|
the following steps:
|
|
|
|
@enumerate
|
|
@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 FFmpeg, 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
|
|
|
|
You can use the command @code{make lcov-reset} to reset the coverage
|
|
measurements. You will need to rerun @code{make lcov} after running a
|
|
new test.
|
|
|
|
@section Using Valgrind
|
|
|
|
The configure script provides a shortcut for using valgrind to spot bugs
|
|
related to memory handling. Just add the option
|
|
@code{--toolchain=valgrind-memcheck} or @code{--toolchain=valgrind-massif}
|
|
to your configure line, and reasonable defaults will be set for running
|
|
FATE under the supervision of either the @strong{memcheck} or the
|
|
@strong{massif} tool of the valgrind suite.
|
|
|
|
In case you need finer control over how valgrind is invoked, use the
|
|
@code{--target-exec='valgrind <your_custom_valgrind_options>} option in
|
|
your configure line instead.
|
|
|
|
@anchor{Release process}
|
|
@chapter 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{https://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}
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@section Criteria for Point Releases
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Changes that match the following criteria are valid candidates for
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inclusion into a point release:
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@enumerate
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@item
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Fixes a security issue, preferably identified by a @strong{CVE
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number} issued by @url{http://cve.mitre.org/}.
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@item
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Fixes a documented bug in @url{https://trac.ffmpeg.org}.
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@item
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Improves the included documentation.
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@item
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Retains both source code and binary compatibility with previous
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point releases of the same release branch.
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@end enumerate
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The order for checking the rules is (1 OR 2 OR 3) AND 4.
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@section Release Checklist
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The release process involves the following steps:
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@enumerate
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@item
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Ensure that the @file{RELEASE} file contains the version number for
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the upcoming release.
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@item
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Add the release at @url{https://trac.ffmpeg.org/admin/ticket/versions}.
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@item
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Announce the intent to do a release to the mailing list.
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@item
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Make sure all relevant security fixes have been backported. See
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@url{https://ffmpeg.org/security.html}.
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@item
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Ensure that the FATE regression suite still passes in the release
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branch on at least @strong{i386} and @strong{amd64}
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(cf. @ref{Regression tests}).
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@item
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Prepare the release tarballs in @code{bz2} and @code{gz} formats, and
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supplementing files that contain @code{gpg} signatures
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@item
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Publish the tarballs at @url{https://ffmpeg.org/releases}. Create and
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push an annotated tag in the form @code{nX}, with @code{X}
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containing the version number.
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@item
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Propose and send a patch to the @strong{ffmpeg-devel} mailing list
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with a news entry for the website.
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@item
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Publish the news entry.
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@item
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Send an announcement to the mailing list.
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@end enumerate
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@bye
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