Outline of the Standard MIDI File Structure

Go to: [ header chunk | track chunk | track event | meta event | system exclusive event | variable length values ]

A standard MIDI file is composed of "chunks". It starts with a header chunk and is followed by one or more track chunks. The header chunk contains data that pertains to the overall file. Each track chunk defines a logical track.

 
   SMF = <header_chunk> + <track_chunk> [+ <track_chunk> ...]

A chunk always has three components, similar to Microsoft RIFF files (the only difference is that SMF files are big-endian, while RIFF files are usually little-endian). The three parts to each chunk are:

  1. The track ID string which is four charcters long. For example, header chunk IDs are "MThd", and Track chunk IDs are "MTrk".
  2. next is a four-byte unsigned value that specifies the number of bytes in the data section of the track (part 3).
  3. finally comes the data section of the chunk. The size of the data is specified in the length field which follows the chunk ID (part 2).

Header Chunk


Track Chunk


Variable Length Values

Several different values in SMF events are expressed as variable length quantities (e.g. delta time values). A variable length value uses a minimum number of bytes to hold the value, and in most circumstances this leads to some degree of data compresssion.

A variable length value uses the low order 7 bits of a byte to represent the value or part of the value. The high order bit is an "escape" or "continuation" bit. All but the last byte of a variable length value have the high order bit set. The last byte has the high order bit cleared. The bytes always appear most significant byte first.

Here are some examples:

   Variable length              Real value
   0x7F                         127 (0x7F)
   0x81 0x7F                    255 (0xFF)
   0x82 0x80 0x00               32768 (0x8000)
Related Files
Web : MIDI Manufacturers Association
Midi Editor : Free Online MIDI Editor