- Sound: the default output's pulse monitor (what the headset plays) as AAC in the same fMP4; the
player starts muted (browser autoplay rules) with a Sound on button. Video timestamps go to the
wall clock (-ts mono2abs) instead of forcing it on the pulse input, which gave bursts of AAC packets
one shared timestamp; aresample=async=1 keeps the sound continuous.
- Late viewers start at a keyframe of the video track (audio samples are all sync).
- Qualities 360p/480p/720p/1080p scale down only; 'full' sends SteamVR's headset view at its own
size (1920x1080 today; v4l2cam has no size option, so 2K/4K would only upscale).
- Player keeps a 0.3 s cushion and catches up at 1.1x; it seeks only when >2 s behind (seeking to the
very edge starved playback).