Instrumented worker-3: even on the ordered FORCE_SHM download path, Mutter
re-delivers COMPLETE OLD pool buffers — 655 frames in a 15 s session whose content
exactly matched an earlier frame (not damage-incremental; full old frames, in
runs, ~45% during motion). NVIDIA gives no fence to prevent it, so the producer
delivery can't be made clean from our side.
Detect it and drop it: hash a spatial sample of each captured frame; a frame whose
content equals an EARLIER distinct frame (vs the current one, whose duplicates pass
through) is a stale re-delivery — skip it so the encoder never emits the flash
(try_latest re-sends the last good frame; brief hold instead of a backward jump).
Runs on the CPU/SHM path (where Mutter+NVIDIA capture lives); never triggers on
static content or non-Mutter compositors (no reverts). PUNKTFUNK_KEEP_STALE=1
disables it for A/B.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler
731eb9ad8c