Re: how to access HAL buffer timestamps when using AUHAL?
Re: how to access HAL buffer timestamps when using AUHAL?
- Subject: Re: how to access HAL buffer timestamps when using AUHAL?
- From: "Ross Bencina" <email@hidden>
- Date: Wed, 22 Jul 2009 14:23:37 +1000
Thanks Jeff...
Is there any way to query CoreAudio for the hardware latency? e.g. the
time
difference from when a sample enters the audio hardware at
inOutputTime->mHostTime to when it appears as a voltage or optical
impulse
on the physical output?
The HAL provides the properties kAudioDevicePropertyLatency and
kAudioStreamPropertyLatency. The latency for any particular channel on an
audio device is the sum of the device latency and the latency of the
stream the channel is in.
Sorry, just to check that I understand, for audio output, are these
invariants correct?
inNow->mHostTime - scheduling jitter == scheduledIoProcTime
scheduled IoProcTime + [kAudioStreamPropertyLatency] ==
inOutputTime->mHostTime
scheduled IoProcTime + [kAudioStreamPropertyLatency] +
[kAudioDevicePropertyLatency] == analog voltage output from DAC time
Note that AUHAL proxies most of the HAL's properties, so you can access
them straight from AUHAL without dipping down to the HAL's API.
Thanks
Ross.
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