clear description of AudioTimeStamp?
clear description of AudioTimeStamp?
- Subject: clear description of AudioTimeStamp?
- From: Kurt Bigler <email@hidden>
- Date: Fri, 18 Apr 2003 18:26:02 -0700
Is there somewhere a good description of the AudioTimeStamp fields?
Searching developer.apple.com for AudioTimeStamp yields only one match, that
being the coreaudio.pdf file which contains almost no description at all. I
believe I searched the list archives and did not find much, but apologies if
I missed something obvious.
In particicular:
Is mHostTime the estimated host time at which the first sample in the buffer
appears at the actual device output or input, based on latency info
presumably provided to the HAL by the driver? I assume this must be the
case, otherwise the AudioTimeStamp would not seem to be of much use for
synchronizing devices.
Does mSampleTime start at zero for the first sample read/written after a
device is started? Does the same apply when the device is seen through an
output audio unit?
I would also like to understand what happens to both mSampleTime and
mHostTime when a kAudioDeviceProcessorOverload occurs. In particular, if I
have callbacks for several devices I would like to be able to recover the
buffering relationship between the several sample-synchronized devices after
one of the devices has an overload. This is for a performance situation (in
which recovery matters), not a recording situation (in which you would give
up and start over). Do I have to stop all the devices and start them again?
(That would be bad.) Or can I assume that the gap in mSampleTime reflects
how much the overloaded device has slipped in buffering relative to the
other devices? Or is mSampleTime for some reason unreliable, so that I must
look at the mHostTime field of all the devices and convert this back to
samples to recover the correct buffering relationship?
Thanks,
Kurt Bigler
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