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Matroska (or actually EBML) uses variable-length numbers where only seven bits of every byte is usable for the length; the other bits encode the length of the variable-length number. So in order to find out how many bytes one needs to encode a given number one can use a loop like while (num >> 7 * bytes) bytes++; the Matroska muxer effectively did this. Yet it has a disadvantage: It is impossible for the result of a single right shift of an unsigned number with most significant bit set to be zero, because one can only shift by 0..(width - 1). On some architectures like x64 it is not even possible to do it with undefined right shifts in which case this leads to an infinite loop. This can be easily avoided by switching to a loop whose condition is (num >>= 7). The maximum value the so modified function can return is 10; any value > 8 is invalid and will now lead to an assert in put_ebml_num() or in start_ebml_master() (or actually in put_ebml_size_unknown()). Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com> (cherry picked from commit 9b0f9003dfab6a230d46aaa94091bf509d889f37)
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.