Re: clear description of AudioTimeStamp?
Re: clear description of AudioTimeStamp?
- Subject: Re: clear description of AudioTimeStamp?
- From: Jeff Moore <email@hidden>
- Date: Tue, 22 Apr 2003 11:24:50 -0700
On Monday, April 21, 2003, at 11:30 PM, Kurt Bigler wrote:
I am finding that I am getting kAudioDeviceProcessorOverload
nofications
with no gaps in mSampleTime.
Checking for gaps in mSampleTime seemed like the obvious thing to do,
since
I need to know the number of samples skipped in order to resynchronize
my
buffers.
However, it appears that mHostTime is showing a gap that is at least
approximately correct. So it looks like I am stuck with scaling
mHostTime
in order to determine the number of scamples skipped, which seems
absurd.
This sounds like a manifestation of a bug I found the other day that
caused the HAL to send too many overload notifications under certain
circumstances or an overload notification when what really happened was
that the driver returned an error from the kernel trap.
Is mRateScalar by any chance useful for this? This appears to be
another
field of AudioTimeStamp that is undocumented, except for the phrase
"system
rate scalar".
The rate scalar field, which only started getting filled out with 10.2,
indicates the ratio of the actual sample rate to the nominal sample
rate.
Otherwise I have to use the function that converts host time to nanos,
divide by 10e9, and multply by the sample rate.
No matter what, if the rounding to integer does not work out right,
then I
am stuck.
Is there supposed to be a gap in mSampleTime? Is the fact that there
is no
gap a problem with the driver or with the HAL? I kind of remember
reading
that the HAL just passed on values from the driver in the
AudioTimeStamp.
I think you are bumping into the bug I mentioned. But in general, there
will be a gap in the sample time as well as the host time.
--
Jeff Moore
Core Audio
Apple
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