NVENC ran CBR (bit_rate == max_bit_rate, rc=cbr) but never set rc_buffer_size,
so it used a loose default VBV. A high-motion P-frame was then allowed to spike
to many times the average frame size; the extra packets overflow the depth-2
send queue (newest frame dropped) and the kernel UDP buffer (WouldBlock drops),
which the client sees as framedrops/jitter — and on the infinite-GOP GameStream
path as old/stale frames flashing until the next RFI.
Set a tight ~1-frame VBV (rc_buffer_size = bitrate/fps) so the encoder holds
frame size roughly constant and absorbs motion as a momentary QP/quality dip
instead — the Sunshine/Moonlight low-latency model. Tunable via
PUNKTFUNK_VBV_FRAMES (default 1.0); larger trades burst tolerance for motion
quality. Fixes both the punktfunk/1 and GameStream paths (shared encoder).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler
9a4ac6ff60