what does AVMediaTypeMuxed mean?

Question

Simple question: what does AVMediaTypeMuxed mean?

I'm looking at some sample code (below) and it doesn't return anything on my iPad 2. So is AVMediaTypeMuxed a device media type that only exists on the iPhone?

AVCaptureDevice *muxedDevice = [AVCaptureDevice defaultDeviceWithMediaType: AVMediaTypeMuxed];
if (muxedDevice) {
    NSLog (@"got muxedDevice");
    AVCaptureDeviceInput *muxedInput = [AVCaptureDeviceInput deviceInputWithDevice:muxedDevice
                                                                             error:&setUpError];
    if (muxedInput) {
        [captureSession addInput:muxedInput];
    }
}

Answer 1

mux is a shortened version of multiplex; muxed media is therefore media where multiple streams have been combined together into a single stream — usually that means audio and video streams are combined into a single byte stream.

I would therefore be unsurprised if there's no default multiplexed media output device, as Apple may simply have decided that the default inputs are the cameras and the microphone separately.