OggMIDI

Mapping for embedding MIDI data streams in Ogg.

This mapping was designed by Jack Moffitt. See this mailing list post for documentation of his scheme.

= Header packet

OggMIDI streams have a single header packet for codec identification.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1| Byte
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier 'OggMIDI\0'                                        | 0-3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               | 4-7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        version number         |         time format           | 8-11
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           timebase            |                                 12-13
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The header packet begins with the character sequence 'OggMIDI\0' for codec identification.

This is followed by an 8 bit version field. The version must be 0 for the mapping described here.

The time format field is also 8 bits, and describes the timestamp format used by the midi data. It is interpreted as follows:

• 1 one beat per quarter note
• 24, 25, 29, 30, (50, 59, 60?) corresponding smpte frame
• other values are undefined

The timebase occupies the final 16 bits and gives the number of ticks per time format unit.

= Data packets

The header packet is followed by a series of data packets, each of which contains an integral number of midi events.