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The blend functions currently convert strides from bytes to elements of the type by using the stride /= sizeof(pixel) idiom. Yet this has several drawbacks: 1. It invokes undefined behavior that happens to work when stride is negative: size_t is typically the unsigned type of ptrdiff_t and therefore the division will be performed as size_t, i.e. use logical right shifts, making stride very big when sizeof(pixel) is > 1. This works, because pointer to pixel for accesses entails an implicit factor of sizeof(pixel) so that everything is correct modulo SIZE_MAX. Yet this is UB and UBSan complains about it. 2. It makes the compiler emit actual shifts/ands to discard the low bits shifted away. 3. There may be systems where alignof(uint16_t) or alignof(float) is strictly smaller than their sizeof, so that the stride (in bytes) is not guaranteed to be multiple of these sizeofs. In this case, dividing by sizeof(pixel) is simply wrong. Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.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 means to alter decoded audio and video through a directed graph of connected 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.