Following is what I think about, if anyincorrect, please help to point out, thanks

The function of Capture and Playback of aUSB audio device, it means USB host can do the capture and playback by usingthe interface of the USB audio device.

About the terminals, here only for inputand output terminal of a USB audio device. Both of them are only said from USBaudio device said. For example, how can we get the current sample rate for theCapture function?

First of all, we need to parse the outputterminal descriptor and get the source ID, then lpIssueVendorTransfer. Why isoutput terminal, but input terminal?

As I said just now, termianl only for USBaudio device, but not for USB host. The capture function, for USB audio device,it means USB audio device get the raw audio data and transfer it to USB host,so output terminal is for the Capture function said from USB audio device side.

As same, for the Playback function, audiodata transferred from USB host to USB audio device, so from USB audio deviceside, the audio data is input.