Problems implementing kAudioDevicePropertyIOProcStreamUsage property in a user-land CoreAudio device
Problems implementing kAudioDevicePropertyIOProcStreamUsage property in a user-land CoreAudio device
- Subject: Problems implementing kAudioDevicePropertyIOProcStreamUsage property in a user-land CoreAudio device
- From: Stéphane Letz <email@hidden>
- Date: Wed, 22 Oct 2008 11:22:56 +0200
Hi,
Our user-land CoreAudio device implements the
kAudioDevicePropertyIOProcStreamUsage property: it defines it as
"Settable" (implementing the IsPropertySettable method) then
implements the SetPropertyData method for
kAudioDevicePropertyIOProcStreamUsage.
We have some problems when our device is used by iTunes. Basically as
soon as our device allows more than 2 output channels, iTunes restrict
the use to 2 output channels using the
kAudioDevicePropertyIOProcStreamUsage property (and no input
channels), but then iTunes does not play correctly anymore (no sound
and time does not advance)
1) Our first implementation was to have a channels layout defined as
the *maximum* number of input/output our device could handle; thus the
AudioBufferList layout for input and output channels was allocated
accordingly and given as the parameters for the audio IOCproc of our
device. This does not work as explained.
2) We then tried to have a channel layout that *exactly* match what
IOProcStreamUsage the application wants, that is we allocate
AudioBufferList layout for input and output to be exactly what the
kAudioDevicePropertyIOProcStreamUsage property has defined. This does
not work either.
3) QuickTime Player is less sensitive: it works in 1) and 2) cases
4) It we just desactivate the kAudioDevicePropertyIOProcStreamUsage
property implementation (not Settable" anymore and so on...) then our
device keeps the maximum input and output that have been defined and
iTunes the works correctly again, using the first 2 output channels
of the device
There is something that we don't do correctly in our implementation.
What can be the problem?
Thanks
Stephane Letz
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