They're both 39 seconds of music, but the MPEG version is 50 times as
long as the MIDI!
Why's that?
MIDI is a recording of the notes played,
MPEG is a recording of the sound made.
MIDI is played back by having your computer make the sound of the note played,
MPEG plays back the sound.
Therefore, with MIDI, the sound will vary on different computers depending on the ability of a computer's hardware and software. MPEG sounds fairly consistent but it takes a lot more memory. The sound must be sampled thousands of times a second rather than the relatively slow events that are recorded for MIDI.