Multichannel Devices With mChannelsPerFrame == 1?
Multichannel Devices With mChannelsPerFrame == 1?
- Subject: Multichannel Devices With mChannelsPerFrame == 1?
- From: "Puhl, Scott" <email@hidden>
- Date: Tue, 15 Apr 2008 19:26:45 -0500
- Acceptlanguage: en-US
- Thread-topic: Multichannel Devices With mChannelsPerFrame == 1?
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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