iSight timestamp mRateScalar inverted
iSight timestamp mRateScalar inverted
- Subject: iSight timestamp mRateScalar inverted
- From: Michael Thornburgh <email@hidden>
- Date: Sun, 2 May 2004 15:37:21 -0700
(note: already bugreported, #3640684)
so i've been playing around with the Varispeed AU to do sample rate
correction, based on the mRateScalar field of the inInputTime and
inOutputTime timestamps in the IOProc. it seems that the rate scalar
is the ratio of nominal sample rate to actual sample rate; that is, if
the device is supposed to be 44100 Hz and it's actually 44097.5 Hz, the
rate scalar is 1.00005669.
however, in the IOProc for an iSight, the mRateScalar field appears to
be the inverse of that -- for a nominal rate of 48000 Hz and an actual
rate of 47995.6 Hz, you'll get an mRateScalar of 0.9999083. so
attempting to correct using this value will drive you further away from
actual.
not counting the iSight, i'm getting pretty swell sample rate
conversion & correction results using an AUVarispeed hooked up to an
AUConverter and the timestamp mRateScalars.
fyi.
-mike
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