Deep research (OBS Studio's linux-pipewire, Mutter bug tracker) found the GNOME
stale-frame flash is a buffer-RECYCLING race, not damage (Mutter sends whole
frames, no SPA_META_VideoDamage) and not buffer count. OBS's proven fix is
latest-frame-only dequeue: each process callback, drain ALL queued PipeWire
buffers, requeue the older ones, and consume only the NEWEST — plus skip
CORRUPTED buffers. Our code dequeued one buffer per callback (oldest-first) and
the bounded channel dropped the NEWEST when full, so during Mutter's bursty
delivery the encoder got stale frames → the flash.
Switch the process callback to raw dequeue_raw_buffer + drain-to-newest (requeue
older), extract the consume logic into consume_frame(spa_buf) sourcing datas via
the transparent Data cast, skip SPA_META_HEADER_FLAG_CORRUPTED / CORRUPTED-chunk
buffers (size-0 skip kept SHM-only so dmabuf isn't regressed), and remove the
earlier content-hash drop heuristic (it couldn't tell stale re-deliveries from
legit repeating content). Diagnostic logs drain depth + chunk/header flags.
Reverts none of the FORCE_SHM / dmabuf_fence work.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler
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