The midi/out device class consists of MIDI sequencers that are used for output. You access these devices by using the MIDI functions, which are described in the Platform SDK.
The lineGetID and phoneGetID functions fill a VARSTRING structure, setting the dwStringFormat member to the STRINGFORMAT_BINARY value and appending this additional member:
DWORD DeviceId; // identifier of MIDI device
The DeviceId member is the identifier of a closed MIDI device. You use this identifier in a call to the midiOutOpen function to open the device for output. You can use the resulting device handle to play MIDI data at the line or phone device.