MIDI (Musical Instrument Digital Interface) is a technical standard that describes a protocol, digital interface, and connectors that allow a wide variety of electronic musical instruments, computers, and other related devices to connect and communicate with one another. MIDI data is the information sent and received over a MIDI connection, which typically includes note messages, controller values, and other data that can be used to control or generate sound.
This example handlers three different kids of sound data: an audio in file (that contains an mp3 file), an audio source (which can be an audio interface) or a link to your Ableton. A fourth option is to use TD Ableton, but therefore your will need Ableton Suite.
The following link shows a tutorial by Mathew Ragan where ‘ buttons create a movie crossfader between 4 movieFile Ins: https://matthewragan.com/2015/03/29/ame-394-simple-vj-set-up-touchdesigner/.