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- \input texinfo @c -*- texinfo -*-
- @documentencoding UTF-8
- @settitle Developer Documentation
- @titlepage
- @center @titlefont{Developer Documentation}
- @end titlepage
- @top
- @contents
- @chapter Introduction
- 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
- 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
- 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
- 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
- @section Language
- FFmpeg is mainly programmed in the ISO C11 language, except for the public
- headers which must stay C99 compatible.
- 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.
- The following C99 features must not be used anywhere in the codebase:
- @itemize @bullet
- @item
- variable-length arrays;
- @item
- complex numbers;
- @item
- mixed statements and declarations.
- @end itemize
- @subsection SIMD/DSP
- @anchor{SIMD/DSP}
- 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 and RISC-V.
- @end itemize
- 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'.
- @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 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.
- All structures and their member variables should be documented, too.
- Avoid Qt-style and similar Doxygen syntax with @code{!} in it, i.e. replace
- @code{//!} with @code{///} and similar. Also @@ syntax should be employed
- for markup commands, i.e. use @code{@@param} and not @code{\param}.
- @example
- /**
- * @@file
- * MPEG codec.
- * @@author ...
- */
- /**
- * Summary sentence.
- * more text ...
- * ...
- */
- typedef struct Foobar @{
- int var1; /**< var1 description */
- int var2; ///< var2 description
- /** var3 description */
- int var3;
- @} Foobar;
- /**
- * Summary sentence.
- * more text ...
- * ...
- * @@param my_parameter description of my_parameter
- * @@return return value description
- */
- int myfunc(int my_parameter)
- ...
- @end example
- @anchor{Naming conventions}
- @section Naming conventions
- 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.
- 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.
- 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
- No namespacing for identifiers with file and lower scope (e.g. local variables,
- static functions), and struct and union members,
- @item
- 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 visible outside of file scope, used internally
- across multiple libraries, use @code{avpriv_} as prefix, for example,
- @samp{avpriv_report_missing_feature}.
- @item
- 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
- 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
- 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
- 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
- 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
- @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
- area changed: short 1 line description
- details describing what and why and giving references.
- @end example
- 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 Credit any researchers
- If a commit/patch fixes an issues found by some researcher, always credit the
- researcher in the commit message for finding/reporting the issue.
- @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.
- @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 How to setup git send-email?
- Please see @url{https://git-send-email.io/}.
- For gmail additionally see @url{https://shallowsky.com/blog/tech/email/gmail-app-passwds.html}.
- @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{codec_id.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_contents.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}
- @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
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