Trixter, have you any idea how far this (presumably new compression) technique could be pushed? For instance, might "TV quality" be possible with say a 12MHz 286?
Yes, with limitations. The basic techniques (which I'm still writing up, sorry it's taking so long) can be easily applied to any chunky mode (Tandy 320x200x16, MCGA 320x200x256) and datarate, but you run into disk bandwidth issues if you're trying to do too much. Once you hit a certain CPU power threshold, it makes more sense to switch to something else (such as Cinepak, or a custom algorithm based on vector quantization). For example, a 386-25 can play back 160x120 Cinepak @ 30fps while not exceeding a datarate of 150KB/s, so that's definitely the point at which you switch to something like that.
My technique can easily be ported to Tandy 320x200x16 and have it still perform nearly as well as it does in Domination, but until I get a Tandy DAC system, I have no real hardware to test on, sorry. I'll be releasing source and instructions after I finish the write-up, so if someone else wants to take up the charge, I'd be tickled.
I imagine this applies to PWM techniques, but what about LPC or CVSD playback using the PCjr Speech Adapter?
If the sidecar can play audio independently of the CPU, it should be possible. And I think it can, looking at the tech ref quickly. But I won't be tackling that any time soon, sorry And besides, it would only sound decent for voice.