Pausing rendering in the background left mpv decoding every frame
(hardware decode plus copy back) only to drop it, keeping a 1080p video
at ~15% CPU with the screen off. After 5 s in the background without PiP
the video track is now disabled (vid=no); returning to the foreground
re-enables it and seeks exactly to the current position, which keeps
audio and video in sync (avsync 0.000 vs -0.044 and 22 drops without the
seek). Streams loaded while backgrounded start with video disabled.
Background CPU drops to ~3.7% on an iPhone 12 mini.
cdcbe51370