Re: hardware output latency
Re: hardware output latency
- Subject: Re: hardware output latency
- From: Jeff Moore <email@hidden>
- Date: Fri, 19 May 2006 12:08:51 -0700
The total latency for a given stream on the device is the sum of the
device latency and the stream latency. This means that a given device
can have different amounts of latency for each of it's streams.
From <CoreAudio/AudioHardware.h>:
@constant kAudioDevicePropertyLatency
A UInt32 containing the number of frames of
latency in the AudioDevice. Note
that input and output latency may differ.
Further, the AudioDevice's
AudioStreams may have additional latency so
they should be queried as well.
If both the device and the stream say they
have latency, then the total
latency for the stream is the device latency
summed with the stream latency.
@constant kAudioStreamPropertyLatency
A UInt32 containing the number of frames of
latency in the AudioStream. Note
that the owning AudioDevice may have
additional latency so it should be
queried as well. If both the device and the
stream say they have latency,
then the total latency for the stream is the
device latency summed with the
stream latency.
On May 19, 2006, at 3:52 AM, Steve Checkoway wrote:
After rereading
http://lists.apple.com/archives/coreaudio-api/2004/Oct/msg00261.html
(and I can't believe that I remembered this post in the first
place) and looking at my code, I realize that perhaps I
misunderstood when I first wrote it. I was assuming that the
out_hw_latency was the sum of the device latency and the stream
latency. Looking at the numbers reported, this seems incorrect as
they are the same.
Should I be using the sum, the max, or just one of them (in
addition to the safety offset and buffer size, of course) in my
latency calculation?
Actually, reading
http://lists.apple.com/archives/coreaudio-api/2004/Oct/msg00135.html
makes me wonder if I should even be using the safety offset in the
latency calculation. That calculation is used for "start mixing
sound x such that it will become audible exactly at time y."
I realize this has been beaten to death on this list over the past
few years and I apologize. I'd like to just get this right and not
worry about it any more. Frankly, I can't hear any differences that
small, but that doesn't mean that no one can.
--
Jeff Moore
Core Audio
Apple
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Coreaudio-api mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden