Re: Multichannel Devices With mChannelsPerFrame == 1?
Re: Multichannel Devices With mChannelsPerFrame == 1?
- Subject: Re: Multichannel Devices With mChannelsPerFrame == 1?
- From: William Stewart <email@hidden>
- Date: Tue, 15 Apr 2008 17:36:27 -0700
How are you talking to the device?
If you are using the AUHAL audio unit that should be pretty straight
forward. If you are talking to the HAL API directly, then you have
alot of complexity to deal with. AUHAL would be my recommendation
Bill
On Apr 15, 2008, at 5:26 PM, Puhl, Scott wrote:
I'm using an AudioConverter to send my app's internal audio data
stream to the output device, and am seeing some odd behavior with
several pieces of external audio hardware. These problem units are
reporting their format description to be lpcm with only one channel
per frame.
For instance, the Focusrite Saffire LE external firewire device
exhibits the following:
dataSize = sizeof(formatDesc);
err = AudioDeviceGetProperty(deviceID, 0, false,
kAudioDevicePropertyStreamFormat, &dataSize, &formatDesc);
formatDesc
.mSampleRate == 48000
.mFormatID == 'lpcm'
.mFormatFlags == 11
.mBytesPerPacket == 4
.mFramesPerPacket == 1
.mBytesPerFrame == 4
.mChannelsPerFrame == 1
.mBitsPerChannel == 32
.mreserved == 149
Most devices report >1 (usually 2-10) for mChannelsPerFrame. When a
converter is created using this single-channel data, the resultant
stream is then also single-channel.
I know the Saffire is a multiple channel device, but it doesn't
report itself to be one through AudioDeviceGetProperty() for the
kAudioDevicePropertyStreamFormat property id.
Is there another way I should be querying this info from the device?
This code cannot at this time be modified to use AUGraph technology
to handle audio output, so that is not a workable solution for me.
Thank You,
Scott
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