.RMI File Format – RIFF container

The RIFF header

When the size runs past the end of the file, the file has been cut short; the explorer reads what is there and says so. Bytes after the end of the RIFF chunk are not part of the file.

Chunks

Every chunk inside has the same layout:

Some writers leave out the pad byte after a chunk of odd size. When the byte after such a chunk is not zero and starts what looks like a chunk ID, the explorer takes it that the pad was left out and says so.

The data chunk

The data chunk holds a complete Standard MIDI File, byte for byte, starting MThd, in its own big-endian layout:

• Chunks and header – the MThd header and the chunks of the MIDI file
• Track chunks and events – delta times, running status and timing
• Channel messages – notes, controllers, programs and pitch bend
• Meta events – names, text, tempo and signatures
• System exclusive events – sysex messages, packets and escapes

Readers find the chunk by its ID. RP-029 and SF2 RMIDI put it first, at offset 12, so the MIDI file usually starts at offset 20, but other chunks may come before it. The chunk’s size is the length of the MIDI file. A file without a data chunk is not an RMI file; if there is a second one, readers use the first.

LIST INFO

A LIST chunk begins with a four-character list type. For INFO, the rest is a series of sub-chunks, each with the chunk layout and padding above, holding text that ends in a zero byte. These are the standard RIFF INFO IDs:

SF2 RMIDI adds entries of its own:

The explorer shows text entries as Windows-1252, without the closing zero.

Instrument banks

An RMI file can carry the instruments to play the song with, as a nested RIFF chunk:

RP-029 says an RMI file holds one MIDI file, at most one DLS bank and supplemental data such as a version and copyright text. Files with an embedded bank seem to be rare. The banks’ own formats are not described here, and the explorer shows them as bytes.