Attempting to write multiple tracks to a single MIDI file results in broken files that get rejected by most software. The reason is that the writer states it uses N tracks but puts the messages of all those tracks into a single MTrk, effectively omitting the other N-1 MTrks entries.
Attempting to write multiple tracks to a single MIDI file results in broken files that get rejected by most software. The reason is that the writer states it uses N tracks but puts the messages of all those tracks into a single MTrk, effectively omitting the other N-1 MTrks entries.