SMB1 Music Format
02/19/06
by JaSp
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SongParts are the different sections of a song; songs aren't stored with data only so that it can
play a same part without having to write it twice or more. For example, the main theme is composed
of 33 parts following each other, with 10 different parts (from 0x792D to 0x794D). Headers contains
the song part's tempo and the different channel pointers : the main is direct in little endian format
(high-low) and is for square1. The others are for square2, triangle and noise, they're relative to
the first byte of the main channel. Then you've got the data itself.
I didn't search how and where the number of part for the songs are determined. This music format is
similar (but not exactly the same, some instruments data may differ for example, so it'll sound like
garbage if past in another game) to some other games, such as SMB2 or SMB3.
To easily recognize this data, use FCEUXD's Code/Data Logger : start it before a song plays, then
get the whole song to reach its end and search for some blue data in the hex editor, you should
easily find it.

0x791D -> 0x7967	#SongPart HeaderPointers

0x791D + #SongPart HeaderPointer(1 byte) = #SongPart Header(6 bytes)

#SongPart Header : AA BB CC DD EE FF (6 bytes)
AA:	Tempo
BB,CC:	Main SongPart Pointer in RAM (square1 channel)(direct;little endian)(decrease by $8000 to get ROM address)
DD:	Square2 channel pointer (relative; main songpart address + DD)
EE:	Triangle channel pointer (relative; main songpart address + EE)
FF:	Noise channel pointer (relative; main songpart address + FF)

SongPart data
$00		End the whole part (if in square1 data)
$01 - $7F	Note byte (pitch varies according to value)
$80 - $FF	Properties byte
	 		#1aaabbbb
			 aaa  : instrument
			 bbbb : note length