audio callback intervals
audio callback intervals
- Subject: audio callback intervals
- From: Kurt Bigler <email@hidden>
- Date: Tue, 05 Mar 2002 23:27:40 -0800
Could an application that uses CoreAudio reasonably expect that audio
callbacks come at approximately equal intervals? Or might the implementor
of audio hardware/driver combination be free to trigger its callbacks at
unequal intervals if that were more convenient for the hardware
implementation?
So basically it comes down to a question of whether the application
developer is responsible for implementing audio computations that allow for
irregular callback intervals.
I bring this up because I am on the ASIO list and apparently there are
Windows audio devices with ASIO drivers which produce callbacks at unequal
intervals that average out to the correct rate. In the specific example
given on the ASIO list the callbacks were separated by either 16ms or 32ms,
but have the correct average spacing of 21.3ms.
Also, I am aware that isochronous transfers on a Firewire bus occur in
bursts that are not evenly spaced but have the correct average rate. So
conceivably a driver for audio over firewire might want to present the data
as it becomes available which might not be at equal intervals, and leave it
up to the application to do the best thing with this for its own purposes.
I would personally like to see a policy that HAL and AudioUnit callbacks
always come at equal intervals, making application development easier and
forcing the drivers to deal with the ideosyncracies of the implementation.
Is there such an expectation? Is it a documented official requirement?
Should it be?
Thanks for any input.
-Kurt Bigler
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