[astrange]

> The standard provides for arithmetic coding, but no one implements it because of the patent.

That is, there is an implementation in the libjpeg source tree, but it's disabled. I thought the patent had actually expired now, though.

Also, H.264's arithmetic coding mode saves ~20% bitrate; Vorbis or AAC could presumably benefit too, but neither of them use an arithmetic coder, even though AAC should have no patent problems. Maybe there's some technical problem I don't know about.