You can enjoy not only listening but also viewing.
MIDITrail supports Standard MIDI File (format 0/1), and CoreMIDI.
Requirements: iOS 5.1
(1) Preparing MIDI files
You have to transfer MIDI files to your iOS device from Mac or PC.
Connect your iOS device to Mac or PC, and launch iTunes.
Then you can transfer MIDI files using 'File Sharing'.
(2) Preparing Sound module
MIDITrail does not have software synth.
You have to prepare sound module which supports CoreMIDI. There are two ways as shown below:
The first way is to connect MIDI interface device and external sound module. (e.g. iRig MIDI, i-MX1, etc.)
The second way is to use Synth App which supports 'Virtual MIDI Port' and 'Background Mode'. (e.g. bs-16i, etc.)