Codecs are sometimes named after really ridiculous things. Actimagine has named it after nerve agent. Or Panasonic VCR tape format that’s only Wickedpedia has heard about. But I bet on nerve agent (if you didn’t have to study chemical warfare weapons at school then you’re not born in the USSR and be thankful for that).
First of all, I don’t know much about VX except that it was used on game consoles. Also judging by the code it was intended to be used with really low resolutions because it had stride hardcoded to 256 from what I’ve seen.
It reminds me of Mobiclip HD somewhat. I’m too lazy to investigate all details (because I only have an ARM disassembly of some binary with some helpful comments) but here’s what I could find after spending an hour or two on it.
Video codec employs exp-Golomb codes for most things — signed and unsigned ones, bitreader limits them to 16 bits at most. Again, there’s not much I can say about overall structure except that it looks like simplified H.264/H.265 (though it was obviously well before H.265 times) — there is spatial prediction (four modes only: horizontal/vertical, DC and plane) and there’s macroblock subdivision too (into square blocks only, possible sizes are 4×4, 8×8 or 16×16). It still looks like there’s one motion vector per macroblock with motion vector deltas for subblocks.
Again, noone cares.