Program Name

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The name of the program (ie, patch) used to play the MTrk. This may be different than the Sequence/Track Name. For example, maybe the name of your sequence (ie, Mtrk) is "Butterfly", but since the track is played upon an electric piano patch, you may also include a Program Name of "ELECTRIC PIANO".

Usually, the instruments (ie, patches, tones, banks, etc) are setup on the audio devices via MIDI Program Change and MIDI Bank Select Controller events within the MTrk. So, this event exists merely to provide the user with visual feedback of what particular patch is used for a track. But it can also give a hint to intelligent software if patch remapping needs to be done. For example, if the MIDI file was created on a non-General MIDI instrument, then the MIDI Program Change event will likely contain the wrong value when played on a General MIDI instrument. Intelligent software can use the Program Name event to look up the correct value for the MIDI Program Change event.

Note that len could be a series of bytes since it is expressed as a variable length quantity.