iOS stops Web Audio when the screen locks, so live processing can't reach a
locked phone. For saved songs, EqRender renders the same chain as the live EQ
(5 bands -> level gain -> limiter) offline into a 32 kHz stereo WAV in OPFS
(eq-renders/<id>.wav, written by the OPFS worker's new write op), one song at a
time in the background. Playback then takes the picture from the saved video
(muted) and the sound from that copy in dual mode — plain media playback, so it
continues with the screen locked; live gains are zeroed so nothing is applied
twice. Copies are re-rendered when the EQ curve or a song's loudness changes
and removed when nothing needs applying.
- Level volume is now on by default everywhere (on iPhone it reaches saved
songs through these copies).
- New iPhone-only Settings -> Playback -> Live sound processing (off by
default): live Web Audio EQ/levelling for streamed songs, stops when locked.
- The EQ dialog works on iPhone and explains where the curve applies.
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