The midi out port provides a small current (a few mA) that is used only to drive the photocoupler at the receiver side (per MIDI specifications, transmitter and

The midi out port provides a small current (a few mA) that is used only to drive the photocoupler at the receiver side (per MIDI specifications, transmitter and receiver have to be electrically insulated). It doesn't and can't supply anything else, although in the past some manufacturers produced little out-of-standard devices that took their supply from the MIDI signal, but they were mostly marketing gimmicks. Moreover, MIDI is a digital signal which doesn't carry any status about the media it travels through; I mean, 10 seconds of nobody playing would appear identical to 10 seconds after a pulled cable.