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This speeds up aac_tablegen to a ludicruous degree (~97%), i.e to the point where it can be argued that runtime initialization can always be done instead of hard-coded tables. The only cost is essentially a trivial increase in the stack size. Even if one does not care about this, the patch also improves accuracy as detailed below. Performance: Benchmark obtained by looping 10^4 times over ff_aac_tableinit. Sample benchmark (x86-64, Haswell, GNU/Linux): old: 1295292 decicycles in ff_aac_tableinit, 512 runs, 0 skips 1275981 decicycles in ff_aac_tableinit, 1024 runs, 0 skips 1272932 decicycles in ff_aac_tableinit, 2048 runs, 0 skips 1262164 decicycles in ff_aac_tableinit, 4096 runs, 0 skips 1256720 decicycles in ff_aac_tableinit, 8192 runs, 0 skips new: 21112 decicycles in ff_aac_tableinit, 511 runs, 1 skips 21269 decicycles in ff_aac_tableinit, 1023 runs, 1 skips 21352 decicycles in ff_aac_tableinit, 2043 runs, 5 skips 21386 decicycles in ff_aac_tableinit, 4080 runs, 16 skips 21299 decicycles in ff_aac_tableinit, 8173 runs, 19 skips Accuracy: The previous code was resulting in needless loss of accuracy due to the pow being called in succession. As an illustration of this: ff_aac_pow34sf_tab[3] old : 0.000000000007598092294225 new : 0.000000000007598091426864 real: 0.000000000007598091778545 truncated to float old : 0.000000000007598092294225 new : 0.000000000007598091426864 real: 0.000000000007598091426864 showing that the old value was not correctly rounded. This affects a large number of elements of the array. Patch tested with FATE. Reviewed-by: Rostislav Pehlivanov <atomnuker@gmail.com> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@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.
- ffserver is a multimedia streaming server for live broadcasts.
- 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. Few developers
follow pull requests so they will likely be ignored.