Every play loads the same selected manifest in its own hls.js low-latency
instance (partial segments + blocking playlist reload), so this stresses the
origin/CDN exactly as N simultaneous viewers would.
Join time = attach → first video frame rendered.
Buffer ratio = total rebuffering time ÷ total watch time (lower is better).
Rebuffered plays = plays that stalled at least once after joining.
Start-up error rate = plays that hit a fatal error before the first frame.
In-stream error rate = plays with an error after joining, plus errors per play·minute.