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The magic constants come from the unofficial "ITU-R BS.1770-1 filter specifications"¹ by Raiden (libebur128) which relies on "Parameter Quantization in Direct-Form Recursive Audio Filters"² by Brian Neunaber. The constants seem to include a quantization bias, for example: - Vb is supposed to be exactly √Vh in a high shelf filter - the Pre-filter Gain should likely be 4dB - Pre Q and RLB Q are respectively very close to √½ and ½ Those are not adjusted to prevent the values from drifting away from the official specifications. An alternative to this approach would be to requantize on the fly as proposed by pbelkner³, where the 48kHz code path would use the exact specifications constants while derivating constants for other frequencies. [1]: https://www.scribd.com/document/49991813/ITU-R-BS-1770-1-filters [2]: https://www.scribd.com/document/6531763/Direct-Form-Filter-Parameter-Quantization [3]: https://hydrogenaud.io/index.php?topic=86116.msg740092#msg740092
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.