[Media_api] PortMidi

[Roger Dannenberg]

 > It seems impossible to send other midi events that note and
 > control events - tempo events are meta events and require
 > more byte, however in PortMidi the event is just a typedef
 > of long. Is there a way?

PortMidi is not intended to model higher-level abstractions such as 
tempo, tracks, and sequences. You need to translate beats to real time 
and then schedule events according to this real time.

I use another library, Allegro, to read/write midi files, but this is 
intentionally separated from PortMidi because almost every application 
dealing with some kind of sequence wants to define its own data 
structures. You are welcome to use it if it will help.

You also will probably need to write some kind of scheduler, e.g. if you 
are playing multiple tracks from a midi file, you need to compute when 
each track will produce its next message and manage them in some sort of 
priority queue so that events are interleaved in the proper time order.

-Roger