[adastra22]

When FLAC compresses stereo audio, it does a diff of the left and right channels and compresses that. This often results in a 2x additional compression ratio because the left and right channels are tightly correlated.

Unless things have changed substantially and I missed it, FLAC does not do similar tricks for other multichannel audio modes. Meaning that for surround sound, each channel is independently compressed and it is unable to exploit signal correlation between channels.

Proprietary formats like Dolby on the other hand do support rather intelligent handling of multichannel modes.

FLAC is not solely a distribution format. Indeed as a distribution format it sucks in a number of ways. It is chiefly used as an archival format, and would in fact be ideal as a mastering format if these deficiencies Could be addressed.

[crtasm]

In what ways does flac suck for distribution? All the music I download from Bandcamp is in that format, it works great for me.

[adastra22]

It could be much smaller, maybe 2-3x better compression. Better support for surround sound / multichannel audio. If an AAC stream were used for the lossy predictive stage, then existing hardware acceleration could be used for energy efficient playback.

[crtasm]

How would 2-3x better compression be achievable?

I don't use or desire multichannel audio but that and the hardware acceleration are interesting points.

[adastra22]

FLAC uses 1970’s era compression technology for both compression stages (lossy and residual) in order to conservatively avoid patents in the implementation. Just replace the lossy component with AAC, which is now out of patent protection, and replace Rice coding for the residual with the much better (but was still patented in the 90’s) arithmetic coding. Those two changes should get 2-4x performance improvement, as well as hardware accelerated encoding and playback as a free bonus.

Multichannel audio support is nice because it is often used in distribution of media files sourced from DVD/BluRay. It would be good to have a high quality, free codec for that use.

[crtasm]

Thanks. I would love to see a PoC of this making my music files that much smaller.