Re: Latency
Re: Latency
- Subject: Re: Latency
- From: Brian Willoughby <email@hidden>
- Date: Tue, 28 Dec 2010 21:18:08 -0800
By the way, PresentationLatency is something calculated by an
AudioUnit host and reported to the plugin so that the plugin can get
an idea of any latency between its output and the actual audio
output. It is intended to allow AU UI, such as metering, to be able
to sync graphics with the audio for the user's benefit. You are
technically writing a host, so you have to provide this value based
upon your setup - you cannot request it because there is no code
setting it. I don't think it is appropriate for iOS anyway, since
you can't easily write your own audio units.
The other sources of latency are the plugins and the audio hardware
itself. Each has a different mechanism for requesting the value.
AudioUnit latency should be calculated after you initialize your
graph. Before that, you'll probably get 0. Audio hardware latency
is a different API, and you might have to use a different approach
with the RemoteIO AudioUnit. It appears that you've discovered the
API for that scenario.
By the way, the above is just a rough summary from memory - I may
have a few details wrong. I just wanted to give an idea of the
various kinds of latency and how their API differ.
Brian Willoughby
Sound Consulting
On Dec 28, 2010, at 18:37, Gregory Wieber wrote:
or kAudioSessionProperty_CurrentHardwareOutputLatency (depending on
whether its input or output)
On Tue, Dec 28, 2010 at 6:37 PM, Gregory Wieber
<email@hidden> wrote:
Wow, sorry -- complete cut-and-paste mistake!
kAudioSessionProperty_CurrentHardwareInputLatency
+ kAudioSessionProperty_PreferredHardwareIOBufferDuration is what
I meant.
On Tue, Dec 28, 2010 at 5:17 PM, Paul Davis
<email@hidden> wrote:
On Tue, Dec 28, 2010 at 8:12 PM, Gregory Wieber
<email@hidden> wrote:
> For the sake of anyone else who may be wondering how to do
this, I believe
> I've found the correct way to determine latency on iOS -- it's
the sum
> of kAudioSessionProperty_PreferredHardwareSampleRate
> + kAudioSessionProperty_PreferredHardwareIOBufferDuration.
i refuse to believe that the use of samplerate (a number in the
range
of 30,000-100,000) is correct in this context. i suspect you've just
latency on the order of 1 second, somehow. i could be wrong.
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