\input texinfo @c -*- texinfo -*-
+@documentencoding UTF-8
@settitle Developer Documentation
@titlepage
@contents
-@chapter Developers Guide
+@chapter Introduction
-@section API
+This text is concerned with the development @emph{of} FFmpeg itself. Information
+on using the FFmpeg libraries in other programs can be found elsewhere, e.g. in:
@itemize @bullet
-@item libavcodec is the library containing the codecs (both encoding and
-decoding). Look at @file{doc/examples/decoding_encoding.c} to see how to use
-it.
+@item
+the installed header files
+@item
+@url{http://ffmpeg.org/doxygen/trunk/index.html, the Doxygen documentation}
+generated from the headers
+@item
+the examples under @file{doc/examples}
+@end itemize
-@item libavformat is the library containing the file format handling (mux and
-demux code for several formats). Look at @file{ffplay.c} to use it in a
-player. See @file{doc/examples/muxing.c} to use it to generate audio or video
-streams.
+For more detailed legal information about the use of FFmpeg in
+external programs read the @file{LICENSE} file in the source tree and
+consult @url{https://ffmpeg.org/legal.html}.
+If you modify FFmpeg code for your own use case, you are highly encouraged to
+@emph{submit your changes back to us}, using this document as a guide. There are
+both pragmatic and ideological reasons to do so:
+@itemize @bullet
+@item
+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.
+@item
+FFmpeg developers include leading experts in the field who can find bugs or
+design flaws in your code.
+@item
+By supporting the project you find useful you ensure it continues to be
+maintained and developed.
@end itemize
-@section Integrating libavcodec or libavformat in your program
+All proposed code changes should be submitted for review to
+@url{mailto:ffmpeg-devel@@ffmpeg.org, the development mailing list}, as
+described in more detail in the @ref{Submitting patches} chapter. The code
+should comply with the @ref{Development Policy} and follow the @ref{Coding Rules}.
+The developer making the commit and the author are responsible for their changes
+and should try to fix issues their commit causes.
+
+@anchor{Coding Rules}
+@chapter Coding Rules
-You can integrate all the source code of the libraries to link them
-statically to avoid any version problem. All you need is to provide a
-'config.mak' and a 'config.h' in the parent directory. See the defines
-generated by ./configure to understand what is needed.
+@section Language
-You can use libavcodec or libavformat in your commercial program, but
-@emph{any patch you make must be published}. The best way to proceed is
-to send your patches to the FFmpeg mailing list.
+FFmpeg is mainly programmed in the ISO C99 language, extended with:
+@itemize @bullet
+@item
+Atomic operations from C11 @file{stdatomic.h}. They are emulated on
+architectures/compilers that do not support them, so all FFmpeg-internal code
+may use atomics without any extra checks. However, @file{stdatomic.h} must not
+be included in public headers, so they stay C99-compatible.
+@end itemize
-@section Contributing
+Compiler-specific extensions may be used with good reason, but must not be
+depended on, i.e. the code must still compile and work with compilers lacking
+the extension.
-There are 3 ways by which code gets into ffmpeg.
+The following C99 features must not be used anywhere in the codebase:
@itemize @bullet
-@item Submitting Patches to the main developer mailing list
- see @ref{Submitting patches} for details.
-@item Directly committing changes to the main tree.
-@item Committing changes to a git clone, for example on github.com or
- gitorious.org. And asking us to merge these changes.
+@item
+variable-length arrays;
+
+@item
+complex numbers;
+
+@item
+mixed statements and declarations.
@end itemize
-Whichever way, changes should be reviewed by the maintainer of the code
-before they are committed. And they should follow the @ref{Coding Rules}.
-The developer making the commit and the author are responsible for their changes
-and should try to fix issues their commit causes.
+@subsection SIMD/DSP
+@anchor{SIMD/DSP}
-@anchor{Coding Rules}
-@section Coding Rules
+As modern compilers are unable to generate efficient SIMD or other
+performance-critical DSP code from plain C, handwritten assembly is used.
+Usually such code is isolated in a separate function. Then the standard approach
+is writing multiple versions of this function – a plain C one that works
+everywhere and may also be useful for debugging, and potentially multiple
+architecture-specific optimized implementations. Initialization code then
+chooses the best available version at runtime and loads it into a function
+pointer; the function in question is then always called through this pointer.
+
+The specific syntax used for writing assembly is:
+@itemize @bullet
+@item
+NASM on x86;
+
+@item
+GAS on ARM.
+@end itemize
-@subsection Code formatting conventions
+A unit testing framework for assembly called @code{checkasm} lives under
+@file{tests/checkasm}. All new assembly should come with @code{checkasm} tests;
+adding tests for existing assembly that lacks them is also strongly encouraged.
+
+@subsection Other languages
+
+Other languages than C may be used in special cases:
+@itemize @bullet
+@item
+Compiler intrinsics or inline assembly when the code in question cannot be
+written in the standard way described in the @ref{SIMD/DSP} section. This
+typically applies to code that needs to be inlined.
+
+@item
+Objective-C where required for interacting with macOS-specific interfaces.
+@end itemize
+
+@section Code formatting conventions
There are the following guidelines regarding the indentation in files:
+
@itemize @bullet
@item
Indent size is 4.
+
@item
The TAB character is forbidden outside of Makefiles as is any
form of trailing whitespace. Commits containing either will be
rejected by the git repository.
+
@item
You should try to limit your code lines to 80 characters; however, do so if
and only if this improves readability.
+
+@item
+K&R coding style is used.
@end itemize
The presentation is one inspired by 'indent -i4 -kr -nut'.
-The main priority in FFmpeg is simplicity and small code size in order to
-minimize the bug count.
+@subsection Vim configuration
+In order to configure Vim to follow FFmpeg formatting conventions, paste
+the following snippet into your @file{.vimrc}:
+@example
+" indentation rules for FFmpeg: 4 spaces, no tabs
+set expandtab
+set shiftwidth=4
+set softtabstop=4
+set cindent
+set cinoptions=(0
+" Allow tabs in Makefiles.
+autocmd FileType make,automake set noexpandtab shiftwidth=8 softtabstop=8
+" Trailing whitespace and tabs are forbidden, so highlight them.
+highlight ForbiddenWhitespace ctermbg=red guibg=red
+match ForbiddenWhitespace /\s\+$\|\t/
+" Do not highlight spaces at the end of line while typing on that line.
+autocmd InsertEnter * match ForbiddenWhitespace /\t\|\s\+\%#\@@<!$/
+@end example
-@subsection Comments
+@subsection Emacs configuration
+For Emacs, add these roughly equivalent lines to your @file{.emacs.d/init.el}:
+@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")
+@end lisp
+
+@section Comments
Use the JavaDoc/Doxygen format (see examples below) so that code documentation
can be generated automatically. All nontrivial functions should have a comment
above them explaining what the function does, even if it is just one sentence.
* more text ...
* ...
*/
-typedef struct Foobar@{
+typedef struct Foobar @{
int var1; /**< var1 description */
int var2; ///< var2 description
/** var3 description */
...
@end example
-@subsection C language features
+@anchor{Naming conventions}
+@section Naming conventions
-FFmpeg is programmed in the ISO C90 language with a few additional
-features from ISO C99, namely:
-@itemize @bullet
-@item
-the @samp{inline} keyword;
-@item
-@samp{//} comments;
-@item
-designated struct initializers (@samp{struct s x = @{ .i = 17 @};})
-@item
-compound literals (@samp{x = (struct s) @{ 17, 23 @};})
-@end itemize
+Names of functions, variables, and struct members must be lowercase, using
+underscores (_) to separate words. For example, @samp{avfilter_get_video_buffer}
+is an acceptable function name and @samp{AVFilterGetVideo} is not.
-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.
+Struct, union, enum, and typedeffed type names must use CamelCase. All structs
+and unions should be typedeffed to the same name as the struct/union tag, e.g.
+@code{typedef struct AVFoo @{ ... @} AVFoo;}. Enums are typically not
+typedeffed.
-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:
+Enumeration constants and macros must be UPPERCASE, except for macros
+masquerading as functions, which should use the function naming convention.
+
+All identifiers in the libraries should be namespaced as follows:
@itemize @bullet
@item
-mixing statements and declarations;
-@item
-@samp{long long} (use @samp{int64_t} instead);
-@item
-@samp{__attribute__} not protected by @samp{#ifdef __GNUC__} or similar;
-@item
-GCC statement expressions (@samp{(x = (@{ int y = 4; y; @})}).
-@end itemize
+No namespacing for identifiers with file and lower scope (e.g. local variables,
+static functions), and struct and union members,
-@subsection Naming conventions
-All names are using underscores (_), not CamelCase. For example, @samp{avfilter_get_video_buffer} is
-a valid function name and @samp{AVFilterGetVideo} is not. The exception from this are type names, like
-for example structs and enums; they should always be in the CamelCase
-
-
-There are following conventions for naming variables and functions:
-@itemize @bullet
@item
-For local variables no prefix is required.
+The @code{ff_} prefix must be used for variables and functions visible outside
+of file scope, but only used internally within a single library, e.g.
+@samp{ff_w64_demuxer}. This prevents name collisions when FFmpeg is statically
+linked.
+
@item
-For variables and functions declared as @code{static} no prefixes are required.
+For variables and functions visible outside of file scope, used internally
+across multiple libraries, use @code{avpriv_} as prefix, for example,
+@samp{avpriv_report_missing_feature}.
+
@item
-For variables and functions used internally by the library, @code{ff_} prefix
-should be used.
-For example, @samp{ff_w64_demuxer}.
+All other internal identifiers, like private type or macro names, should be
+namespaced only to avoid possible internal conflicts. E.g. @code{H264_NAL_SPS}
+vs. @code{HEVC_NAL_SPS}.
+
@item
-For variables and functions used internally across multiple libraries, use
-@code{avpriv_}. For example, @samp{avpriv_aac_parse_header}.
+Each library has its own prefix for public symbols, in addition to the
+commonly used @code{av_} (@code{avformat_} for libavformat,
+@code{avcodec_} for libavcodec, @code{swr_} for libswresample, etc).
+Check the existing code and choose names accordingly.
+
@item
-For exported names, each library has its own prefixes. Just check the existing
-code and name accordingly.
+Other public identifiers (struct, union, enum, macro, type names) must use their
+library's public prefix (@code{AV}, @code{Sws}, or @code{Swr}).
@end itemize
-@subsection Miscellanous conventions
+Furthermore, name space reserved for the system should not be invaded.
+Identifiers ending in @code{_t} are reserved by
+@url{http://pubs.opengroup.org/onlinepubs/007904975/functions/xsh_chap02_02.html#tag_02_02_02, POSIX}.
+Also avoid names starting with @code{__} or @code{_} followed by an uppercase
+letter as they are reserved by the C standard. Names starting with @code{_}
+are reserved at the file level and may not be used for externally visible
+symbols. If in doubt, just avoid names starting with @code{_} altogether.
+
+@section Miscellaneous conventions
+
@itemize @bullet
@item
-fprintf and printf are forbidden in libavformat and libavcodec,
-please use av_log() instead.
-@item
Casts should be used only when necessary. Unneeded parentheses
should also be avoided if they don't make the code easier to understand.
@end itemize
-@subsection Editor configuration
-In order to configure Vim to follow FFmpeg formatting conventions, paste
-the following snippet into your @file{.vimrc}:
+@anchor{Development Policy}
+@chapter Development Policy
+
+@section Code behaviour
+
+@subheading Correctness
+The code must be valid. It must not crash, abort, access invalid pointers, leak
+memory, cause data races or signed integer overflow, or otherwise cause
+undefined behaviour. Error codes should be checked and, when applicable,
+forwarded to the caller.
+
+@subheading Thread- and library-safety
+Our libraries may be called by multiple independent callers in the same process.
+These calls may happen from any number of threads and the different call sites
+may not be aware of each other - e.g. a user program may be calling our
+libraries directly, and use one or more libraries that also call our libraries.
+The code must behave correctly under such conditions.
+
+@subheading Robustness
+The code must treat as untrusted any bytestream received from a caller or read
+from a file, network, etc. It must not misbehave when arbitrary data is sent to
+it - typically it should print an error message and return
+@code{AVERROR_INVALIDDATA} on encountering invalid input data.
+
+@subheading Memory allocation
+The code must use the @code{av_malloc()} family of functions from
+@file{libavutil/mem.h} to perform all memory allocation, except in special cases
+(e.g. when interacting with an external library that requires a specific
+allocator to be used).
+
+All allocations should be checked and @code{AVERROR(ENOMEM)} returned on
+failure. A common mistake is that error paths leak memory - make sure that does
+not happen.
+
+@subheading stdio
+Our libraries must not access the stdio streams stdin/stdout/stderr directly
+(e.g. via @code{printf()} family of functions), as that is not library-safe. For
+logging, use @code{av_log()}.
+
+@section Patches/Committing
+@subheading Licenses for patches must be compatible with FFmpeg.
+Contributions should be licensed under the
+@uref{http://www.gnu.org/licenses/lgpl-2.1.html, LGPL 2.1},
+including an "or any later version" clause, or, if you prefer
+a gift-style license, the
+@uref{http://opensource.org/licenses/isc-license.txt, ISC} or
+@uref{http://mit-license.org/, MIT} license.
+@uref{http://www.gnu.org/licenses/gpl-2.0.html, GPL 2} including
+an "or any later version" clause is also acceptable, but LGPL is
+preferred.
+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.
+
+@subheading You must not commit code which breaks FFmpeg!
+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.
+
+@subheading Commit messages
+Commit messages are highly important tools for informing other developers on
+what a given change does and why. Every commit must always have a properly
+filled out commit message with the following format:
@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 set noexpandtab shiftwidth=8 softtabstop=8
-" Trailing whitespace and tabs are forbidden, so highlight them.
-highlight ForbiddenWhitespace ctermbg=red guibg=red
-match ForbiddenWhitespace /\s\+$\|\t/
-" Do not highlight spaces at the end of line while typing on that line.
-autocmd InsertEnter * match ForbiddenWhitespace /\t\|\s\+\%#\@@<!$/
-@end example
+area changed: short 1 line description
-For Emacs, add these roughly equivalent lines to your @file{.emacs.d/init.el}:
-@example
-(c-add-style "ffmpeg"
- '("k&r"
- (c-basic-offset . 4)
- (indent-tabs-mode . nil)
- (show-trailing-whitespace . t)
- (c-offsets-alist
- (statement-cont . (c-lineup-assignments +)))
- )
- )
-(setq c-default-style "ffmpeg")
+details describing what and why and giving references.
@end example
-@section Development Policy
+If the commit addresses a known bug on our bug tracker or other external issue
+(e.g. CVE), the commit message should include the relevant bug ID(s) or other
+external identifiers. Note that this should be done in addition to a proper
+explanation and not instead of it. Comments such as "fixed!" or "Changed it."
+are not acceptable.
+
+When applying patches that have been discussed at length on the mailing list,
+reference the thread in the commit message.
+
+@subheading Testing must be adequate but not excessive.
+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.
+
+@subheading Do not commit unrelated changes together.
+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.
+
+@subheading Cosmetic changes should be kept in separate patches.
+We refuse source indentation and other cosmetic changes if they are mixed
+with functional changes, such commits will be rejected and removed. Every
+developer has his own indentation style, you should not change it. Of course
+if you (re)write something, you can use your own style, even though we would
+prefer if the indentation throughout FFmpeg was consistent (Many projects
+force a given indentation style - we do not.). If you really need to make
+indentation changes (try to avoid this), separate them strictly from real
+changes.
+
+NOTE: If you had to put if()@{ .. @} over a large (> 5 lines) chunk of code,
+then either do NOT change the indentation of the inner part within (do not
+move it to the right)! or do so in a separate commit
+
+@subheading Credit the author of the patch.
+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.
+
+@subheading Always wait long enough before pushing changes
+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!
+
+@section Code
+@subheading Warnings for correct code may be disabled if there is no other option.
+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.
+
+@section Library public interfaces
+Every library in FFmpeg provides a set of public APIs in its installed headers,
+which are those listed in the variable @code{HEADERS} in that library's
+@file{Makefile}. All identifiers defined in those headers (except for those
+explicitly documented otherwise), and corresponding symbols exported from
+compiled shared or static libraries are considered public interfaces and must
+comply with the API and ABI compatibility rules described in this section.
+
+Public APIs must be backward compatible within a given major version. I.e. any
+valid user code that compiles and works with a given library version must still
+compile and work with any later version, as long as the major version number is
+unchanged. "Valid user code" here means code that is calling our APIs in a
+documented and/or intended manner and is not relying on any undefined behavior.
+Incrementing the major version may break backward compatibility, but only to the
+extent described in @ref{Major version bumps}.
+
+We also guarantee backward ABI compatibility for shared and static libraries.
+I.e. it should be possible to replace a shared or static build of our library
+with a build of any later version (re-linking the user binary in the static
+case) without breaking any valid user binaries, as long as the major version
+number remains unchanged.
+
+@subsection Adding new interfaces
+Any new public identifiers in installed headers are considered new API - this
+includes new functions, structs, macros, enum values, typedefs, new fields in
+existing structs, new installed headers, etc. Consider the following
+guidelines when adding new APIs.
+
+@subsubheading Motivation
+While new APIs can be added relatively easily, changing or removing them is much
+harder due to abovementioned compatibility requirements. You should then
+consider carefully whether the functionality you are adding really needs to be
+exposed to our callers as new public API.
+
+Your new API should have at least one well-established use case outside of the
+library that cannot be easily achieved with existing APIs. Every library in
+FFmpeg also has a defined scope - your new API must fit within it.
+
+@subsubheading Replacing existing APIs
+If your new API is replacing an existing one, it should be strictly superior to
+it, so that the advantages of using the new API outweight the cost to the
+callers of changing their code. After adding the new API you should then
+deprecate the old one and schedule it for removal, as described in
+@ref{Removing interfaces}.
+
+If you deem an existing API deficient and want to fix it, the preferred approach
+in most cases is to add a differently-named replacement and deprecate the
+existing API rather than modify it. It is important to make the changes visible
+to our callers (e.g. through compile- or run-time deprecation warnings) and make
+it clear how to transition to the new API (e.g. in the Doxygen documentation or
+on the wiki).
+
+@subsubheading API design
+The FFmpeg libraries are used by a variety of callers to perform a wide range of
+multimedia-related processing tasks. You should therefore - within reason - try
+to design your new API for the broadest feasible set of use cases and avoid
+unnecessarily limiting it to a specific type of callers (e.g. just media
+playback or just transcoding).
+
+@subsubheading Consistency
+Check whether similar APIs already exist in FFmpeg. If they do, try to model
+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.
-@enumerate
@item
- Contributions should be licensed under the LGPL 2.1, including an
- "or any later version" clause, or the MIT license. GPL 2 including
- an "or any later version" clause is also acceptable, but LGPL is
- preferred.
-@item
- You must not commit code which breaks FFmpeg! (Meaning unfinished but
- enabled code which breaks compilation or compiles but does not work or
- breaks the regression tests)
- You can commit unfinished stuff (for testing etc), but it must be disabled
- (#ifdef etc) by default so it does not interfere with other developers'
- work.
-@item
- You do not have to over-test things. If it works for you, and you think it
- should work for others, then commit. If your code has problems
- (portability, triggers compiler bugs, unusual environment etc) they will be
- reported and eventually fixed.
-@item
- Do not commit unrelated changes together, split them into self-contained
- pieces. Also do not forget that if part B depends on part A, but A does not
- depend on B, then A can and should be committed first and separate from B.
- Keeping changes well split into self-contained parts makes reviewing and
- understanding them on the commit log mailing list easier. This also helps
- in case of debugging later on.
- Also if you have doubts about splitting or not splitting, do not hesitate to
- ask/discuss it on the developer mailing list.
-@item
- Do not change behavior of the programs (renaming options etc) or public
- API or ABI without first discussing it on the ffmpeg-devel mailing list.
- Do not remove functionality from the code. Just improve!
-
- Note: Redundant code can be removed.
-@item
- Do not commit changes to the build system (Makefiles, configure script)
- which change behavior, defaults etc, without asking first. The same
- applies to compiler warning fixes, trivial looking fixes and to code
- maintained by other developers. We usually have a reason for doing things
- the way we do. Send your changes as patches to the ffmpeg-devel mailing
- list, and if the code maintainers say OK, you may commit. This does not
- apply to files you wrote and/or maintain.
-@item
- We refuse source indentation and other cosmetic changes if they are mixed
- with functional changes, such commits will be rejected and removed. Every
- developer has his own indentation style, you should not change it. Of course
- if you (re)write something, you can use your own style, even though we would
- prefer if the indentation throughout FFmpeg was consistent (Many projects
- force a given indentation style - we do not.). If you really need to make
- indentation changes (try to avoid this), separate them strictly from real
- changes.
-
- NOTE: If you had to put if()@{ .. @} over a large (> 5 lines) chunk of code,
- then either do NOT change the indentation of the inner part within (do not
- move it to the right)! or do so in a separate commit
-@item
- Always fill out the commit log message. Describe in a few lines what you
- changed and why. You can refer to mailing list postings if you fix a
- particular bug. Comments such as "fixed!" or "Changed it." are unacceptable.
- Recommended format:
- area changed: Short 1 line description
-
- details describing what and why and giving references.
-@item
- Make sure the author of the commit is set correctly. (see git commit --author)
- If you apply a patch, send an
- answer to ffmpeg-devel (or wherever you got the patch from) saying that
- you applied the patch.
-@item
- When applying patches that have been discussed (at length) on the mailing
- list, reference the thread in the log message.
-@item
- Do NOT commit to code actively maintained by others without permission.
- Send a patch to ffmpeg-devel instead. If no one answers within a reasonable
- timeframe (12h for build failures and security fixes, 3 days small changes,
- 1 week for big patches) then commit your patch if you think it is OK.
- Also note, the maintainer can simply ask for more time to review!
-@item
- Subscribe to the ffmpeg-cvslog mailing list. The diffs of all commits
- are sent there and reviewed by all the other developers. Bugs and possible
- improvements or general questions regarding commits are discussed there. We
- expect you to react if problems with your code are uncovered.
-@item
- Update the documentation if you change behavior or add features. If you are
- unsure how best to do this, send a patch to ffmpeg-devel, the documentation
- maintainer(s) will review and commit your stuff.
-@item
- Try to keep important discussions and requests (also) on the public
- developer mailing list, so that all developers can benefit from them.
-@item
- Never write to unallocated memory, never write over the end of arrays,
- always check values read from some untrusted source before using them
- as array index or other risky things.
-@item
- Remember to check if you need to bump versions for the specific libav*
- parts (libavutil, libavcodec, libavformat) you are changing. You need
- to change the version integer.
- Incrementing the first component means no backward compatibility to
- previous versions (e.g. removal of a function from the public API).
- Incrementing the second component means backward compatible change
- (e.g. addition of a function to the public API or extension of an
- existing data structure).
- Incrementing the third component means a noteworthy binary compatible
- change (e.g. encoder bug fix that matters for the decoder).
-@item
- Compiler warnings indicate potential bugs or code with bad style. If a type of
- warning always points to correct and clean code, that warning should
- be disabled, not the code changed.
- Thus the remaining warnings can either be bugs or correct code.
- If it is a bug, the bug has to be fixed. If it is not, the code should
- be changed to not generate a warning unless that causes a slowdown
- or obfuscates the code.
-@item
- If you add a new file, give it a proper license header. Do not copy and
- paste it from a random place, use an existing file as template.
-@end enumerate
+Performing ABI- but not API-breaking changes, like reordering struct contents.
+@end itemize
-We think our rules are not too hard. If you have comments, contact us.
+@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.
-Note, these rules are mostly borrowed from the MPlayer project.
+We think our rules are not too hard. If you have comments, contact us.
@anchor{Submitting patches}
-@section 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 :-)
+@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
Run the @ref{Regression tests} before submitting a patch in order to verify
it does not cause unexpected problems.
-Patches should be posted as base64 encoded attachments (or any other
-encoding which ensures that the patch will not be trashed during
-transmission) to the ffmpeg-devel mailing list, see
-@url{http://lists.ffmpeg.org/mailman/listinfo/ffmpeg-devel}
-
It also helps quite a bit if you tell us what the patch does (for example
'replaces lrint by lrintf'), and why (for example '*BSD isn't C99 compliant
and has no lrint()')
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
send a reminder by email. Your patch should eventually be dealt with.
-@section New codecs or formats checklist
+@chapter New codecs or formats checklist
@enumerate
@item
- Did you use av_cold for codec initialization and close functions?
+Did you use av_cold for codec initialization and close functions?
+
@item
- Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
- AVInputFormat/AVOutputFormat struct?
+Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or
+AVInputFormat/AVOutputFormat struct?
+
@item
- Did you bump the minor version number (and reset the micro version
- number) in @file{libavcodec/version.h} or @file{libavformat/version.h}?
+Did you bump the minor version number (and reset the micro version
+number) in @file{libavcodec/version.h} or @file{libavformat/version.h}?
+
@item
- Did you register it in @file{allcodecs.c} or @file{allformats.c}?
+Did you register it in @file{allcodecs.c} or @file{allformats.c}?
+
@item
- Did you add the AVCodecID to @file{avcodec.h}?
- When adding new codec IDs, also add an entry to the codec descriptor
- list in @file{libavcodec/codec_desc.c}.
+Did you add the AVCodecID to @file{avcodec.h}?
+When adding new codec IDs, also add an entry to the codec descriptor
+list in @file{libavcodec/codec_desc.c}.
+
@item
- If it has a fourCC, did you add it to @file{libavformat/riff.c},
- even if it is only a decoder?
+If it has a FourCC, did you add it to @file{libavformat/riff.c},
+even if it is only a decoder?
+
@item
- Did you add a rule to compile the appropriate files in the Makefile?
- Remember to do this even if you're just adding a format to a file that is
- already being compiled by some other rule, like a raw demuxer.
+Did you add a rule to compile the appropriate files in the Makefile?
+Remember to do this even if you'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}?
+Did you add an entry to the table of supported formats or codecs in
+@file{doc/general.texi}?
+
@item
- Did you add an entry in the Changelog?
+Did you add an entry in the Changelog?
+
@item
- If it depends on a parser or a library, did you add that dependency in
- configure?
+If it depends on a parser or a library, did you add that dependency in
+configure?
+
@item
- Did you @code{git add} the appropriate files before committing?
+Did you @code{git add} the appropriate files before committing?
+
@item
- Did you make sure it compiles standalone, i.e. with
- @code{configure --disable-everything --enable-decoder=foo}
- (or @code{--enable-demuxer} or whatever your component is)?
+Did you make sure it compiles standalone, i.e. with
+@code{configure --disable-everything --enable-decoder=foo}
+(or @code{--enable-demuxer} or whatever your component is)?
@end enumerate
-@section patch submission checklist
+@chapter Patch submission checklist
@enumerate
@item
- Does @code{make fate} pass with the patch applied?
+Does @code{make fate} pass with the patch applied?
+
@item
- Was the patch generated with git format-patch or send-email?
+Was the patch generated with git format-patch or send-email?
+
@item
- Did you sign off your patch? (git commit -s)
- See @url{http://kerneltrap.org/files/Jeremy/DCO.txt} for the meaning
- of sign off.
+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?
+Did you provide a clear git commit log message?
+
@item
- Is the patch against latest FFmpeg git master branch?
+Is the patch against latest FFmpeg git master branch?
+
@item
- Are you subscribed to ffmpeg-devel?
- (the list is subscribers only due to spam)
+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?
+Have you checked that the changes are minimal, so that the same cannot be
+achieved with a smaller patch and/or simpler final code?
+
@item
- If the change is to speed critical code, did you benchmark it?
+If the change is to speed critical code, did you benchmark it?
+
@item
- If you did any benchmarks, did you provide them in the mail?
+If you did any benchmarks, did you provide them in the mail?
+
@item
- Have you checked that the patch does not introduce buffer overflows or
- other security issues?
+Have you checked that the patch does not introduce buffer overflows or
+other security issues?
+
@item
- Did you test your decoder or demuxer against damaged data? If no, see
- tools/trasher and the noise bitstream filter. Your decoder or demuxer
- should not crash or end in a (near) infinite loop when fed damaged data.
+Did you test your decoder or demuxer against damaged data? If no, see
+tools/trasher, the noise bitstream filter, and
+@uref{http://caca.zoy.org/wiki/zzuf, zzuf}. Your decoder or demuxer
+should not crash, end in a (near) infinite loop, or allocate ridiculous
+amounts of memory when fed damaged data.
+
@item
- Does the patch not mix functional and cosmetic changes?
+Did you test your decoder or demuxer against sample files?
+Samples may be obtained at @url{https://samples.ffmpeg.org}.
+
@item
- Did you add tabs or trailing whitespace to the code? Both are forbidden.
+Does the patch not mix functional and cosmetic changes?
+
@item
- Is the patch attached to the email you send?
+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.
+Is the mime type of the patch correct? It should be text/x-diff or
+text/x-patch or at least text/plain and not application/octet-stream.
+
@item
- If the patch fixes a bug, did you provide a verbose analysis of the bug?
+If the patch fixes a bug, did you provide a verbose analysis of the bug?
+
@item
- If the patch fixes a bug, did you provide enough information, including
- a sample, so the bug can be reproduced and the fix can be verified?
- Note please do not attach samples >100k to mails but rather provide a
- URL, you can upload to ftp://upload.ffmpeg.org
+If the patch fixes a bug, did you provide enough information, including
+a sample, so the bug can be reproduced and the fix can be verified?
+Note please do not attach samples >100k to mails but rather provide a
+URL, you can upload to @url{https://streams.videolan.org/upload/}.
+
@item
- Did you provide a verbose summary about what the patch does change?
+Did you provide a verbose summary about what the patch does change?
+
@item
- Did you provide a verbose explanation why it changes things like it does?
+Did you provide a verbose explanation why it changes things like it does?
+
@item
- Did you provide a verbose summary of the user visible advantages and
- disadvantages if the patch is applied?
+Did you provide a verbose summary of the user visible advantages and
+disadvantages if the patch is applied?
+
@item
- Did you provide an example so we can verify the new feature added by the
- patch easily?
+Did you provide an example so we can verify the new feature added by the
+patch easily?
+
@item
- If you added a new file, did you insert a license header? It should be
- taken from FFmpeg, not randomly copied and pasted from somewhere else.
+If you added a new file, did you insert a license header? It should be
+taken from 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.
+You should maintain alphabetical order in alphabetically ordered lists as
+long as doing so does not break API/ABI compatibility.
+
@item
- Lines with similar content should be aligned vertically when doing so
- improves readability.
+Lines with similar content should be aligned vertically when doing so
+improves readability.
+
@item
- Consider to add a regression test for your code.
+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
+If you added YASM code please check that things still work with --disable-yasm.
+
@item
- Make sure you check the return values of function and return appropriate
- error codes. Especially memory allocation functions like @code{av_malloc()}
- are notoriously left unchecked, which is a serious problem.
+Test your code with valgrind and or Address Sanitizer to ensure it's free
+of leaks, out of array accesses, etc.
@end enumerate
-@section Patch review process
+@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.
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}
-@section 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.
this case, the reference results of the regression tests shall be modified
accordingly].
-@subsection Adding files to the fate-suite dataset
+@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 inlcuded in the fate-suite.
+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 introductionary message for the patch series that you post to
+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}
+@section Criteria for Point Releases
+
+Changes that match the following criteria are valid candidates for
+inclusion into a point release:
+
+@enumerate
+@item
+Fixes a security issue, preferably identified by a @strong{CVE
+number} issued by @url{http://cve.mitre.org/}.
+
+@item
+Fixes a documented bug in @url{https://trac.ffmpeg.org}.
+
+@item
+Improves the included documentation.
+
+@item
+Retains both source code and binary compatibility with previous
+point releases of the same release branch.
+@end enumerate
+
+The order for checking the rules is (1 OR 2 OR 3) AND 4.
+
+
+@section Release Checklist
+
+The release process involves the following steps:
+
+@enumerate
+@item
+Ensure that the @file{RELEASE} file contains the version number for
+the upcoming release.
+
+@item
+Add the release at @url{https://trac.ffmpeg.org/admin/ticket/versions}.
+
+@item
+Announce the intent to do a release to the mailing list.
+
+@item
+Make sure all relevant security fixes have been backported. See
+@url{https://ffmpeg.org/security.html}.
+
+@item
+Ensure that the FATE regression suite still passes in the release
+branch on at least @strong{i386} and @strong{amd64}
+(cf. @ref{Regression tests}).
+
+@item
+Prepare the release tarballs in @code{bz2} and @code{gz} formats, and
+supplementing files that contain @code{gpg} signatures
+
+@item
+Publish the tarballs at @url{https://ffmpeg.org/releases}. Create and
+push an annotated tag in the form @code{nX}, with @code{X}
+containing the version number.
+
+@item
+Propose and send a patch to the @strong{ffmpeg-devel} mailing list
+with a news entry for the website.
+
+@item
+Publish the news entry.
+
+@item
+Send an announcement to the mailing list.
+@end enumerate
@bye
projects / platform / upstream / ffmpeg.git / blobdiff