Re: practical use of UID for USB devices
Re: practical use of UID for USB devices
- Subject: Re: practical use of UID for USB devices
- From: Michael Thornburgh <email@hidden>
- Date: Thu, 29 Sep 2005 11:41:30 -0700
i save both the UID and the device name in the user preferences. if
i can't find the device by UID, then i select a device with a
matching name that has at least one stream in the direction
(recording or playback) that i'm interested in. if you're using
MTCoreAudio, you can get the latter with +[MTCoreAudioDevice
devicesWithName:havingStreamsForDirection:]. for example:
id recordDevice;
recordDevice = [MTCoreAudioDevice deviceWithUID:
@"AppleUSBAudioEngine:Plantronics:Plantronics headset:3b100000:2"];
if(!recordDevice)
recordDevice = [[MTCoreAudioDevice devicesWithName:
@"Plantronics Headset" havingStreamsForDirection:
kMTCoreAudioDeviceRecordDirection] lastObject];
if(!recordDevice)
recordDevice = [MTCoreAudioDevice defaultInputDevice];
note that checking for streams in the direction you care about is
necessary for things like USB audio devices, where the record and
playback sides appear as different audio devices.
-mike
On Sep 29, 2005, at 11:25 AM, Chris Silverberg wrote:
Hi folks,
I work on a VoIP application and use CoreAudio API's for device
capture and selection. In our preferences window, the user can
select their input and output devices, and I save the user's
selection by storing the kAudioDevicePropertyDeviceUID property.
This works pretty well, but there is a problem.
For USB devices, the UID varies based on which USB port the user
selects. For example, if I connect my Plantronics headset to my
PowerBook, depending on which port I plug into, I will get one of
the following UIDs:
AppleUSBAudioEngine:Plantronics:Plantronics headset:1b100000:2
AppleUSBAudioEngine:Plantronics:Plantronics headset:3b100000:2
Clearly the second to last component of the string identifies the
USB port. Although I'm sure this is useful in certain scenarios,
it pretty much prevents the software from being able to save the
user's selected device in a reliable mannor. With two USB ports on
the side of a PowerBook, it's going to be somewhat random which
port a user will use to plug in.
So, does anyone have any advice on how to handle this? Two choices
come to mind... first, I could use
kAudioDevicePropertyDeviceNameCFString instead of the UID which
would probably solve the problem in most or all cases. Secondly, I
could try to match the UID intelligently so that I ignore the
difference between USB ports, but that seems a bit messy and
subject to break in the future.
Is this simply a design flaw with the UID property?
thanks,
Chris
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