The per-process 'hardware session == 1, evict before every new open'
guard was turning every frame's open into a decoder re-open: after
inserting the fresh session, the NEXT frame's pre-open eviction dropped
it again, so no request ever hit the cache ([open] (request) on every
single frame, zero CACHED hits). Every decode then cost a full FFmpeg
session open (~0.5 s) + a keyframe-scanning seek — playback could never
keep up (the 'main viewer barely moves' report; [perf] showed 1.6-2.2 s
per frame).
Hardware VRAM is bounded by the LRU cap (hardware-first eviction at
MAX_CACHED_DECODERS) and the gpu-vram worker-count policy; the eager
pre-open eviction was the regression.
Mike-Solar
7f41570596