SYNC mode on macOS needed a virtual loopback driver (BlackHole, Loopback,
Soundflower) routed through a Multi-Output Device, and shelled out to
'ffmpeg -f avfoundation' to read it. macOS 14.2 lets a process tap the
system mix directly, so do that instead: CATapDescription ->
AudioHardwareCreateProcessTap -> private aggregate device -> IOProc,
straight through ctypes. No driver, no helper binary, no ffmpeg.
The tap hands out native-rate interleaved float32, so the analyser can
now retune its window and band edges when the capture rate differs from
44.1 kHz, and mono-downmixes the frames before the FFT.
A tap that was never granted System Audio Recording permission is
created happily but only ever delivers digital silence: treat that as a
failed capture instead of flat bars, explain it in the status bar and
fall back to the stream tap. A tap that renders nothing *yet* (playback
still starting, or mpv pointed at another device) is not a permanent
failure either - the stream tap covers for a minute, then the tap is
retried.
Drop the avfoundation device enumeration, the loopback-name heuristics
and the microphone safeguards' tests, and document the new permission
and its diagnostics instead.
SYNC mode was Linux-only: it shelled out to parec. On macOS there is no
PulseAudio, so the analyser always fell back to the drifting stream tap.
Capture with 'ffmpeg -f avfoundation' from a loopback input instead
(BlackHole, Loopback, Soundflower, Multi-Output/Aggregate devices are
auto-detected; SOMAFM_SPECTRUM_DEVICE accepts a name or index). Plain
microphones are never auto-selected.
A loopback that nothing is routed into delivers endless digital silence,
so treat ~6 s of all-zero blocks as a dead monitor and fall back to the
stream tap rather than showing frozen bars. parec handling is unchanged.
beefcarver