Developer Documentation

Table of Contents

1 Introduction

This text is concerned with the development of FFmpeg itself. Information on using the FFmpeg libraries in other programs can be found elsewhere, e.g. in:

For more detailed legal information about the use of FFmpeg in external programs read the LICENSE file in the source tree and consult https://ffmpeg.org/legal.html.

If you modify FFmpeg code for your own use case, you are highly encouraged to submit your changes back to us, using this document as a guide. There are both pragmatic and ideological reasons to do so:

  • 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.
  • FFmpeg developers include leading experts in the field who can find bugs or design flaws in your code.
  • By supporting the project you find useful you ensure it continues to be maintained and developed.

All proposed code changes should be submitted for review to the development mailing list, as described in more detail in the Submitting patches chapter. The code should comply with the Development Policy and follow the Coding Rules. The developer making the commit and the author are responsible for their changes and should try to fix issues their commit causes.

2 Coding Rules

2.1 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:

  • variable-length arrays;
  • complex numbers;
  • mixed statements and declarations.

2.1.1 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:

  • NASM on x86;
  • GAS on ARM and RISC-V.

A unit testing framework for assembly called checkasm lives under tests/checkasm. All new assembly should come with checkasm tests; adding tests for existing assembly that lacks them is also strongly encouraged.

2.1.2 Other languages

Other languages than C may be used in special cases:

  • Compiler intrinsics or inline assembly when the code in question cannot be written in the standard way described in the SIMD/DSP section. This typically applies to code that needs to be inlined.
  • Objective-C where required for interacting with macOS-specific interfaces.

2.2 Code formatting conventions

There are the following guidelines regarding the indentation in files:

  • Indent size is 4.
  • 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.
  • You should try to limit your code lines to 80 characters; however, do so if and only if this improves readability.
  • K&R coding style is used.

The presentation is one inspired by ’indent -i4 -kr -nut’.

2.2.1 Vim configuration

In order to configure Vim to follow FFmpeg formatting conventions, paste the following snippet into your .vimrc: 

" 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\+$\|\t/
" Do not highlight spaces at the end of line while typing on that line.
autocmd InsertEnter * match ForbiddenWhitespace /\t\|\s\+\%#\@<!$/

2.2.2 Emacs configuration

For Emacs, add these roughly equivalent lines to your .emacs.d/init.el: 

(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")

2.3 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 ! in it, i.e. replace //! with /// and similar. Also @ syntax should be employed for markup commands, i.e. use @param and not \param. 

/**
 * @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)
...

2.4 Naming conventions

Names of functions, variables, and struct members must be lowercase, using underscores (_) to separate words. For example, ‘avfilter_get_video_buffer’ is an acceptable function name and ‘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. 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:

  • No namespacing for identifiers with file and lower scope (e.g. local variables, static functions), and struct and union members,
  • The ff_ prefix must be used for variables and functions visible outside of file scope, but only used internally within a single library, e.g. ‘ff_w64_demuxer’. This prevents name collisions when FFmpeg is statically linked.
  • For variables and functions visible outside of file scope, used internally across multiple libraries, use avpriv_ as prefix, for example, ‘avpriv_report_missing_feature’.
  • All other internal identifiers, like private type or macro names, should be namespaced only to avoid possible internal conflicts. E.g. H264_NAL_SPS vs. HEVC_NAL_SPS.
  • Each library has its own prefix for public symbols, in addition to the commonly used av_ (avformat_ for libavformat, avcodec_ for libavcodec, swr_ for libswresample, etc). Check the existing code and choose names accordingly.
  • Other public identifiers (struct, union, enum, macro, type names) must use their library’s public prefix (AV, Sws, or Swr).

Furthermore, name space reserved for the system should not be invaded. Identifiers ending in _t are reserved by POSIX. Also avoid names starting with __ or _ followed by an uppercase letter as they are reserved by the C standard. Names starting with _ are reserved at the file level and may not be used for externally visible symbols. If in doubt, just avoid names starting with _ altogether.

2.5 Miscellaneous conventions

  • Casts should be used only when necessary. Unneeded parentheses should also be avoided if they don’t make the code easier to understand.

3 Development Policy

3.1 Code behaviour

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.

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.

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 AVERROR_INVALIDDATA on encountering invalid input data.

Memory allocation

The code must use the av_malloc() family of functions from 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 AVERROR(ENOMEM) returned on failure. A common mistake is that error paths leak memory - make sure that does not happen.

stdio

Our libraries must not access the stdio streams stdin/stdout/stderr directly (e.g. via printf() family of functions), as that is not library-safe. For logging, use av_log().

3.2 Patches/Committing

Licenses for patches must be compatible with FFmpeg.

Contributions should be licensed under the LGPL 2.1, including an "or any later version" clause, or, if you prefer a gift-style license, the ISC or MIT license. 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.

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.

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: 

area changed: short 1 line description

details describing what and why and giving references.

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.

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.

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.

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

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.

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.

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!

3.3 Code

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.

3.4 Library public interfaces

Every library in FFmpeg provides a set of public APIs in its installed headers, which are those listed in the variable HEADERS in that library’s 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 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.

3.4.1 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.

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.

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 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).

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).

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 Naming conventions and be aligned with other similar APIs, if applicable.

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 AVFoo, the standard approach is requiring the caller to always allocate it through a constructor function, typically named 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 - av_foo_free(AVFoo**) that frees the indirectly supplied object (and its contents, if applicable) and writes 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.

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 doc/APIchanges.

Bump the version

Backward-incompatible API or ABI changes require incrementing (bumping) the major version number, as described in 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 #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.

3.4.2 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 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 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 #define FF_API_<FOO> (LIBAVBAR_VERSION_MAJOR < XX) (where XX is the major version in which the API will be removed) in libavbar/version_major.h (version.h in case of libavutil). Then wrap all uses of the deprecated API in #if FF_API_<FOO> .... #endif, so that the code will automatically get disabled once the major version reaches XX. You can also use FF_DISABLE_DEPRECATION_WARNINGS and 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.

3.4.3 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:

  • Removing previously deprecated APIs.
  • Performing ABI- but not API-breaking changes, like reordering struct contents.

3.5 Documentation/Other

Subscribe to the ffmpeg-devel mailing list.

It is important to be subscribed to the 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.

Subscribe to the ffmpeg-cvslog mailing list.

Diffs of all commits are sent to the 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.

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.

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.

Check your entries in MAINTAINERS.

Make sure that no parts of the codebase that you maintain are missing from the 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 MAINTAINERS file.

We think our rules are not too hard. If you have comments, contact us.

4 Submitting patches

First, read the Coding Rules above if you did not yet, in particular the rules regarding patch submission.

When you submit your patch, please use git format-patch or 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 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 ffmpeg-devel mailing list. Use 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 https://patchwork.ffmpeg.org, if your patch does not show up, its mime type likely was wrong.

How to setup git send-email?

Please see https://git-send-email.io/. For gmail additionally see https://shallowsky.com/blog/tech/email/gmail-app-passwds.html.

Sending patches from email clients

Using 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: 

git format-patch -s -o "outputfolder" --add-header "X-Unsent: 1" --suffix .eml --to ffmpeg-devel@ffmpeg.org -1 1a2b3c4d

Now you’ll just need to open the eml file with the email application and execute ’Send’.

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.

5 New codecs or formats checklist

  1. Did you use av_cold for codec initialization and close functions?
  2. Did you add a long_name under NULL_IF_CONFIG_SMALL to the AVCodec or AVInputFormat/AVOutputFormat struct?
  3. Did you bump the minor version number (and reset the micro version number) in libavcodec/version.h or libavformat/version.h?
  4. Did you register it in allcodecs.c or allformats.c?
  5. Did you add the AVCodecID to codec_id.h? When adding new codec IDs, also add an entry to the codec descriptor list in libavcodec/codec_desc.c.
  6. If it has a FourCC, did you add it to libavformat/riff.c, even if it is only a decoder?
  7. 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.
  8. Did you add an entry to the table of supported formats or codecs in doc/general_contents.texi?
  9. Did you add an entry in the Changelog?
  10. If it depends on a parser or a library, did you add that dependency in configure?
  11. Did you git add the appropriate files before committing?
  12. Did you make sure it compiles standalone, i.e. with configure --disable-everything --enable-decoder=foo (or --enable-demuxer or whatever your component is)?

6 Patch submission checklist

  1. Does make fate pass with the patch applied?
  2. Was the patch generated with git format-patch or send-email?
  3. Did you sign-off your patch? (git commit -s) See Sign your work for the meaning of sign-off.
  4. Did you provide a clear git commit log message?
  5. Is the patch against latest FFmpeg git master branch?
  6. Are you subscribed to ffmpeg-devel? (the list is subscribers only due to spam)
  7. Have you checked that the changes are minimal, so that the same cannot be achieved with a smaller patch and/or simpler final code?
  8. If the change is to speed critical code, did you benchmark it?
  9. If you did any benchmarks, did you provide them in the mail?
  10. Have you checked that the patch does not introduce buffer overflows or other security issues?
  11. Did you test your decoder or demuxer against damaged data? If no, see tools/trasher, the noise bitstream filter, and zzuf. Your decoder or demuxer should not crash, end in a (near) infinite loop, or allocate ridiculous amounts of memory when fed damaged data.
  12. Did you test your decoder or demuxer against sample files? Samples may be obtained at https://samples.ffmpeg.org.
  13. Does the patch not mix functional and cosmetic changes?
  14. Did you add tabs or trailing whitespace to the code? Both are forbidden.
  15. Is the patch attached to the email you send?
  16. 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.
  17. If the patch fixes a bug, did you provide a verbose analysis of the bug?
  18. 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 https://streams.videolan.org/upload/.
  19. Did you provide a verbose summary about what the patch does change?
  20. Did you provide a verbose explanation why it changes things like it does?
  21. Did you provide a verbose summary of the user visible advantages and disadvantages if the patch is applied?
  22. Did you provide an example so we can verify the new feature added by the patch easily?
  23. 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.
  24. You should maintain alphabetical order in alphabetically ordered lists as long as doing so does not break API/ABI compatibility.
  25. Lines with similar content should be aligned vertically when doing so improves readability.
  26. 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.
  27. If you added NASM code please check that things still work with –disable-x86asm.
  28. Test your code with valgrind and or Address Sanitizer to ensure it’s free of leaks, out of array accesses, etc.

7 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.

8 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 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].

8.1 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.

8.2 Visualizing Test Coverage

The FFmpeg build system allows visualizing the test coverage in an easy manner with the coverage tools gcov/lcov. This involves the following steps:

  1. Configure to compile with instrumentation enabled: configure --toolchain=gcov.
  2. 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.
  3. Run make lcov to generate coverage data in HTML format.
  4. View lcov/index.html in your preferred HTML viewer.

You can use the command make lcov-reset to reset the coverage measurements. You will need to rerun make lcov after running a new test.

8.3 Using Valgrind

The configure script provides a shortcut for using valgrind to spot bugs related to memory handling. Just add the option --toolchain=valgrind-memcheck or --toolchain=valgrind-massif to your configure line, and reasonable defaults will be set for running FATE under the supervision of either the memcheck or the massif tool of the valgrind suite.

In case you need finer control over how valgrind is invoked, use the --target-exec='valgrind <your_custom_valgrind_options> option in your configure line instead.

9 Release process

FFmpeg maintains a set of release branches, which are the recommended deliverable for system integrators and distributors (such as Linux distributions, etc.). At regular times, a release manager prepares, tests and publishes tarballs on the https://ffmpeg.org website.

There are two kinds of releases:

  1. Major releases always include the latest and greatest features and functionality.
  2. Point releases are cut from release branches, which are named release/X, with X being the release version number.

Note that we promise to our users that shared libraries from any FFmpeg release never break programs that have been compiled against previous versions of 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 ffmpeg-devel mailing list in time to allow forward planning.

9.1 Criteria for Point Releases

Changes that match the following criteria are valid candidates for inclusion into a point release:

  1. Fixes a security issue, preferably identified by a CVE number issued by http://cve.mitre.org/.
  2. Fixes a documented bug in https://trac.ffmpeg.org.
  3. Improves the included documentation.
  4. Retains both source code and binary compatibility with previous point releases of the same release branch.

The order for checking the rules is (1 OR 2 OR 3) AND 4.

9.2 Release Checklist

The release process involves the following steps:

  1. Ensure that the RELEASE file contains the version number for the upcoming release.
  2. Add the release at https://trac.ffmpeg.org/admin/ticket/versions.
  3. Announce the intent to do a release to the mailing list.
  4. Make sure all relevant security fixes have been backported. See https://ffmpeg.org/security.html.
  5. Ensure that the FATE regression suite still passes in the release branch on at least i386 and amd64 (cf. Regression tests).
  6. Prepare the release tarballs in bz2 and gz formats, and supplementing files that contain gpg signatures
  7. Publish the tarballs at https://ffmpeg.org/releases. Create and push an annotated tag in the form nX, with X containing the version number.
  8. Propose and send a patch to the ffmpeg-devel mailing list with a news entry for the website.
  9. Publish the news entry.
  10. Send an announcement to the mailing list.

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