GMID LFD Resource Type
Author: Jagged Fel (jaggedfel621@gmail.com)
Site: http://idmr.empirereborn.net
Updated: 2009.10.05
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The GMID Resource type is special format for MIDI sound files.  After a 32-byte
header the remaining portion continues in the standard MIDI format.

*NOTE* GMID and MIDI data blocks are BIG-ENDIAN in contrast with all other
resource types, ie; 0x1234 is stored as 12 34.  MIDI also uses a annoying
variable-length value storage.  Only the bottom 7 bits are used for data, and
the last bit is used to signify if another byte is used.
0xC4 (11000100) becomes	(10000001 01000100)	0x8148.  This method does allow for
three-byte data terms, but maxes out at 4 bytes.

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GMID Structure

The following values are used through this and all of my file definitions
unless otherwise specified:
NAME	LENGTH	DESC
----	------	----
BYTE	1	unsigned 8-bit
CHAR	1	ASCII character
SHORT	2	signed Int16
INT	4	signed Int32

--
0x00	Header
0x10	CHAR[4]	"MIDI"
0x14	INT	MidiLength	[Big-endian]
0x18	Unknown
	MidiHeader
	MidiData
--

struct Header (size 0x10)
{
	0x0	CHAR[4]	"GMID"
	0x4	CHAR[8]	Name
	0xC	INT	Length
}

struct Unknown
{
	0x0	CHAR[4]	"MDpg"
	0x4	INT	Length
	0x8	BYTE[Length]
}

struct MidiHeader (size 0xE)	[Big-endian]
{
	0x0	CHAR[4]	"MThd"
	0x4	INT	HeaderLength (6)
	0x8	SHORT	FormatType
	0xA	SHORT	NumberOfTracks
	0xC	SHORT	TimeDivison
}

struct MidiData
{
	0x0	CHAR[4]	"MTrk"
	0x4	INT	Length
	0x8	BYTE[Length]	Data
}

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GMID Detail

First off, I'm only going to talk about what is called out above, I'm not going
to go into the MidiData portion because that's a mess. There are tons of
different events in there, all behaving differently, with the stupid variable
sizing, and if you really need to know about that stuff you can find it online
easy enough.

Okay, so once we're beyond the standard Header, we start the data block with
what appears to be just another container file. I found no real references on
GMID files other than it's something LucasArts cooked up. From what I can
tell, you should be able to skip up to the MidiHeader and just start reading
from there, exporting into a MIDI file (.smf) and just leaving it at that. Of
course, without knowing exactly what it is, I'm hesitant to say you can import
at will.
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