changes:
* Powerful channel coupling system takes advantage of similarities between
channels to reduce bitrate.
* Additional encoding modes give more flexibility in bitrate selection.
64,80,96,128,160,192,256,350 stereo; 32,48,64,80,112,140 mono modes.
* Only 44.1KHz/48KHz is officially supported in this release. Lower
sample rates will work, but with much lower quality.
* Cascaded encoding makes libvorbis ready for future bitrate reduction tools.
* Decode engine bugfix ensures better compatibility with future Vorbis codecs.
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