Standard MIDI File (SMF) Format

This format stores the standard MIDI messages (ie, status bytes with appropriate data bytes) plus a time-stamp for each message (ie, a series of bytes that represent how many clock pulses to wait before "playing" the event). The format also allows saving information about tempo, time and key signatures, the names of tracks and patterns, and other information typically needed by a sequencer. One SMF can store information for numerous patterns and tracks so that any sequencer can preserve these structures when loading the file.

NOTE: A track usually is analogous to one musical part, such as a Trumpet part. A pattern would be analogous to all of the musical parts (ie, Trumpet, Drums, Piano, etc) for one song.

The format was designed to be generic so that the most important data can be read by all sequencers. Think of a MIDI file as a musical version of an ASCII text file (except that the MIDI file contains binary data), and the various sequencer programs as text editors all capable of reading that file. But, unlike ASCII, MIDI file format saves data in chunks (ie, groups of bytes preceded by an ID and size) which can be parsed, loaded, skipped, etc. Therefore, SMF format is flexible enough for a particular sequencer to store its own proprietary, "extra" data in such a way that another sequencer won't be confused when loading the file and can safely ignore this extra stuff that it doesn't need. For example, maybe a sequencer wants to save a "flag byte" that indicates whether the user has turned on an audible metronome click. The sequencer can save this flag byte in such a way that another sequencer can skip this byte without having to understand what that byte is for. In the future, the SMF format can also be extended to include new "official" chunks that all sequencer programs may elect to load and use. This can be done without making old data files obsolete, nor making old sequencers no longer able to load the new files. So, the format is designed to be extensible in a backwardly compatible way.

Of course, SMF files may be used by other MIDI software than just sequencers. Since SMF files can store any and all types of MIDI messages, including System Exclusive messages, they may be used to store/load data by all kinds of MIDI software, such as a Patch Editor that wants to save some System Exclusive messages it received from a MIDI module. (The "timestamp" for each message may be irrelevant to such a Patch Editor. But it's easily ignored for programs that don't really need it).