# MIDIReadBlock A block receiving MIDI input. ``` typealias MIDIReadBlock = (UnsafePointer, UnsafeMutableRawPointer?) -> Void ``` ## Parameters `pktlist` The incoming MIDI message(s). `srcConnRefCon` A refCon you passed to MIDIPortConnectSource, which identifies the source of the data. ## Discussion This is a callback block through which a client receives incoming MIDI messages. A MIDIReadBlock is passed to the MIDIInputPortCreateWithBlock and MIDIDestinationCreateWithBlock functions. The CoreMIDI framework will create a high-priority receive thread on your client’s behalf, and from that thread, your MIDIReadProc will be called when incoming MIDI messages arrive. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)