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libavutil/common.h is a public header that provides generic math functions whereas libavutil/intmath.h is a private header that contains plattform-specific optimized versions of said math functions. common.h includes intmath.h (when building the FFmpeg libraries) so that the optimized versions are used for them. This interdependency sometimes causes trouble: intmath.h once contained an inlined ff_sqrt function that relied upon av_log2_16bit. In case there was no optimized logarithm available on this plattform, intmath.h needed to include common.h to get the generic implementation and this has been done after the optimized versions (if any) have been provided so that common.h used the optimized versions; it also needed to be done before ff_sqrt. Yet when intmath.h was included from common.h and if an ordinary inclusion guard was used by common.h, the #include "common.h" in intmath.h was a no-op and therefore av_log2_16bit was still unknown at the end of intmath.h (and also in ff_sqrt) if no optimized version was available. Before a955b5965825631986ba854d007d4e934e466c7d this was solved by duplicating the #ifndef av_log2_16bit check after the inclusion of common.h in intmath.h; said commit instead moved these checks to the end of common.h, outside the inclusion guards and made common.h include itself to get these unguarded defines. This is still the current state of affairs. Yet this is unnecessary since 9734b8ba56d05e970c353dfd5baafa43fdb08024 as said commit removed ff_sqrt as well as the #include "common.h" from intmath.h. Therefore this commit moves everything inside the inclusion guards and makes common.h not include itself. Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
FFmpeg README
FFmpeg is a collection of libraries and tools to process multimedia content such as audio, video, subtitles and related metadata.
Libraries
libavcodecprovides implementation of a wider range of codecs.libavformatimplements streaming protocols, container formats and basic I/O access.libavutilincludes hashers, decompressors and miscellaneous utility functions.libavfilterprovides a mean to alter decoded Audio and Video through chain of filters.libavdeviceprovides an abstraction to access capture and playback devices.libswresampleimplements audio mixing and resampling routines.libswscaleimplements color conversion and scaling routines.
Tools
- ffmpeg is a command line toolbox to manipulate, convert and stream multimedia content.
- ffplay is a minimalistic multimedia player.
- ffprobe is a simple analysis tool to inspect multimedia content.
- Additional small tools such as
aviocat,ismindexandqt-faststart.
Documentation
The offline documentation is available in the doc/ directory.
The online documentation is available in the main website and in the wiki.
Examples
Coding examples are available in the doc/examples directory.
License
FFmpeg codebase is mainly LGPL-licensed with optional components licensed under GPL. Please refer to the LICENSE file for detailed information.
Contributing
Patches should be submitted to the ffmpeg-devel mailing list using
git format-patch or git send-email. Github pull requests should be
avoided because they are not part of our review process and will be ignored.