Midi Keyboard on Nexus 7 though USB on the go OTG Android - YouTube
Amazon.com: MIDI to USB/USB C Interface MIDI Cable Adapter with Input & Output Connecting with Keyboard/Piano/Synthesizer for Editing & Recording with Windows, Android, Mac OS, Android, Most Type-c Devices : Musical Instruments
Amazon.com: TNP MIDI Cable Set to USB with Type C Adapter 2 in 1 MIDI Piano USB Cord from PC to Keyboard, Synthesizer, Electronic Drum, Electric Blow Pipe, 16 Channels for Windows,
3in1 USB MIDI Cable 1.5m - Apple iOS & Android - Piano City
GitHub - kshoji/USB-MIDI-Driver: USB MIDI Driver for Android 3.1 or later
Developing MIDI applications on Android -
AUDIO4c - audio interface for streaming, performance, and recording — iConnectivity