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With 5 accumulator vectors and 6 inputs, this can only use LMUL=2. Also the number of vector loop iterations is small, just 5 on 128-bit vector hardware. The vector loop is somewhat unusual in that it processes data in descending memory order, in order to save on vector slides: in descending order, we can extract elements to carry over to the next iteration from the bottom of the vectors directly. With ascending order (see in the Opus postfilter function), there are no ways to get the top elements directly. On the downside, this requires the use of separate shift and sub (the would-be SH3SUB instruction does not exist), with a small pipeline stall on the vector load address. The edge cases in scalar are done in scalar as this saves on loads and remains significantly faster than C. autocorrelate_c: 669.2 autocorrelate_rvv_f32: 421.0
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.