Rockbox Support for Wavpack Hybrid Compression

Wavpack Hybrid Compression

The Wavpack audio codec supports an unusual "hybrid" compression mode. In this mode, a traditional lossy file is complemented by a "correction" file. When the two are decoded together, the original input bitstream can be recreated exactly. The lossy file may also be decoded on its own.

Rockbox currently handles lossy files but ignores the correction files.

Milestones

• Correctly decode hybrid files on a PC with Rockbox code (complete and verified for stereo files)
• Implement support for buffering two (or more) files in a codec-independent manner (working with bugs)
• Ensure real-time decoding on a Rockbox target (decoding but not real time on target)
• Implement seeking in hybrid files with correction info present (imprecise short-range seeking works)
• Add support for and check more obscure formats, like hybrid mono lossless and old-style hybrid shaping code (mono lossless support complete)

Useful Info

Wavpack spec description: here. Wavpack file format: here.

Current Status

Decoding of stereo hybrid lossless files functions off-target with a patch at http://q3q.us/hybrid2.patch . This does NOT run on a device; use http://q3q.us/codec-executor.tar.bz2 to run the codec!

A patch enabling playback on iPod targets and in the sim is at http://www.rockbox.org/tracker/task/10537 but does not yet run in real time.