Re: Rationale of AudioTimeStamp
Re: Rationale of AudioTimeStamp
- Subject: Re: Rationale of AudioTimeStamp
- From: Jeff Moore <email@hidden>
- Date: Thu, 20 Feb 2003 11:33:28 -0800
The device driver provides a series of time stamps that map out the
sample time's relationship to host time. The HAL has code that takes
that information and can project values between the two time bases.
This is embodied in the API as AudioDeviceTranslateTime(). The HAL uses
this facility to fill out the AudioTimeStamps it passes to each IOProc
it calls. At that level, you will always see the sample time, the host
time, and starting in 10.2, the rate scalar as valid.
It is the intent of the Audio Units to preserve the integrity of the
time stamps they are pulled with when calling their inputs, but I know
that there have been some issues there in the past that I don't know
have been resolved (Bill or Doug might be able to comment more on
that). For other APIs that sit on the HAL, you'll have to consult with
their maintainers as to what the policy is.
On Thursday, February 20, 2003, at 12:14 AM, Andrea Gozzi wrote:
----- Original Message -----
From: "Jeff Moore" <email@hidden>
For instance, the HAL provides both the sample time and the host time
when it calls IOProcs. This reflects the HAL's ability to easily
convert between the two and can be exploited to provide good synch
primitives.
Just curious. Is that an audio device driver task (to provide the host
time
in the IOProc call?), or an OS task?
I found at least one situation where the host time was not provided,
only
sample time....
Andrea
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--
Jeff Moore
Core Audio
Apple
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