[sz3]

Right now, it's both.

The decoder has a lot of image processing work to do (intriguingly well-suited for the GPU), and also lots of popcnts. I've optimized it a fair bit, but there's probably some tricks I still need to learn. It turns out that mobile processors don't like heat very much, and blow out their cache much quicker than you'd hope. :)

In the long run, I think your intuition is correct. The hard physics of the camera constraints (exposure time, etc) will put a hard upper bound on FPS+fidelity, and thus bandwidth.