Re: kAudioDevicePropertyBufferSize reported to IOAudioEngine?
Re: kAudioDevicePropertyBufferSize reported to IOAudioEngine?
- Subject: Re: kAudioDevicePropertyBufferSize reported to IOAudioEngine?
- From: Daniel Mack <email@hidden>
- Date: Thu, 20 Oct 2005 11:47:07 +0200
Hi Jeff, Hi Bill,
Thanks for your reply. After Bill metioned that, I decided to
configure that
value via a proprietary call thru a UserClient command. I'll choose a
proper
value that work safely and leave it up to the user whether to change
this
in a preference pane or not. We'll see if that both satifies the
needs of
users needing very low latencies as well as beeing as stable as
possible for
the rest.
Thanks,
Daniel
On Oct 20, 2005, at 2:16 AM, Jeff Moore wrote:
One other thing that Bill just mentioned to me is that if you want
to use the client IO buffer size as part of the calculation for
your device's safety offset (aka sample offset in the family API),
you have to be darn careful that you don't change the safety offset
while there are clients currently registered. The reason why is
that if you increase the safety offset after a client already is
playing, you will cause that client to glitch when the HAL starts
using the new safety offset. Given that a new client can start
playing at any time with any buffer size, it makes such an
optimization a little less attractive.
Note that you can put a limit on the upper bound of the buffer size
the HAL will allow with the size of the device's ring buffer. The
HAL will only allow clients to use a maximum buffer size of 3/8 the
size of the ring buffer. This can at least allow you to plan for
the worst case scenario and prevent glitching when new clients start.
Finally, changing the safety offset currently requires a major
engine change to be sent before the HAL will notice the new value.
This necessarily makes changing the safety offset a fairly
disruptive procedure that should be avoided except in the course of
doing other configuration changes if possible.
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