Mirror of http://www.smspower.org/music/uploads/Help/vgmspec150.txt.
VGM Spec v1.50
VGM (Video Game Music) is a sample-accurate sound logging format for the Sega
Master System, the Sega Game Gear and possibly many other machines (e.g. Sega
Genesis).
The normal file extension is .vgm but files can also be GZip compressed into
.vgz files. However, a VGM player should atempt to support compressed and
uncompressed files with either extension. (ZLib's GZIO library makes this
trivial to implement.)
The format starts with a 64 byte header:
00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f
0x00 ["Vgm " ident ][EoF offset ][Version ][SN76489 clock ]
0x10 [YM2413 clock ][GD3 offset ][Total # samples][Loop offset ]
0x20 [Loop # samples ][Rate ][SN FB ][SNW]*** [YM2612 clock ]
0x30 [YM2151 clock ][VGM data offset] *** *** *** *** *** *** *** ***
- Unused space (marked with *) is reserved for future expansion, and should be
zero.
- All integer values are *unsigned* and written in "Intel" byte order, so for
example 0x12345678 is written as 0x78 0x56 0x34 0x12.
- All pointer offsets are written as relative to the current position in the
file, so for example the GD3 offset at 0x14 in the header is the file
position of the GD3 tag minus 0x14.
0x00: "Vgm " (0x56 0x67 0x6d 0x20) file identification (32 bits)
0x04: Eof offset (32 bits)
Relative offset to end of file (i.e. file length - 4).
This is mainly used to find the next track when concatanating
player stubs and multiple files.
0x08: Version number (32 bits)
Version 1.50 is stored as 0x00000150, stored as 0x50 0x01 0x00 0x00.
This is used for backwards compatibility in players, and defines which
header values are valid.
0x0c: SN76489 clock (32 bits)
Input clock rate in Hz for the SN76489 PSG chip. A typical value is
3579545. It should be 0 if there is no PSG chip used.
0x10: YM2413 clock (32 bits)
Input clock rate in Hz for the YM2413 chip. A typical value is
3579545. It should be 0 if there us no YM2413 chip used.
0x14: GD3 offset (32 bits)
Relative offset to GD3 tag. 0 if no GD3 tag.
GD3 tags are descriptive tags similar in use to ID3 tags in MP3 files.
See the GD3 specification for more details. The GD3 tag is usually
stored immediately after the VGM data.
0x18: Total # samples (32 bits)
Total of all wait values in the file.
0x1c: Loop offset (32 bits)
Relative offset to loop point, or 0 if no loop.
For example, if the data for the one-off intro to a song was in bytes
0x0040-0x3fff of the file, but the main looping section started at
0x4000, this would contain the value 0x4000-0x1c = 0x00003fe4.
0x20: Loop # samples (32 bits)
Number of samples in one loop, or 0 if there is no loop.
Total of all wait values between the loop point and the end of
the file.
[VGM 1.01 additions:]
0x24: Rate (32 bits)
"Rate" of recording in Hz, used for rate scaling on playback. It is
typically 50 for PAL systems and 60 for NTSC systems. It should be set
to zero if rate scaling is not appropriate - for example, if the game
adjusts its music engine for the system's speed.
VGM 1.00 files will have a value of 0.
[VGM 1.10 additions:]
0x28: SN76489 feedback (16 bits)
The white noise feedback pattern for the SN76489 PSG. Known values are:
0x0009 Sega Master System 2/Game Gear/Mega Drive
(SN76489/SN76496 integrated into Sega VDP chip)
0x0003 Sega Computer 3000H, BBC Micro
(SN76489AN)
For version 1.01 and earlier files, the feedback pattern should be
assumed to be 0x0009. If the PSG is not used then this may be omitted
(left at zero).
0x2a: SN76489 shift register width (8 bits)
The noise feedback shift register width, in bits. Known values are:
16 Sega Master System 2/Game Gear/Mega Drive
(SN76489/SN76496 integrated into Sega VDP chip)
15 Sega Computer 3000H, BBC Micro
(SN76489AN)
For version 1.01 and earlier files, the shift register width should be
assumed to be 16. If the PSG is not used then this may be omitted (left
at zero).
0x2b: Reserved (8 bits)
This should be left at zero.
0x2c: YM2612 clock (32 bits)
Input clock rate in Hz for the YM2612 chip. A typical value is
3579545. It should be 0 if there us no YM2612 chip used.
For version 1.01 and earlier files, the YM2413 clock rate should be
used for the clock rate of the YM2612.
0x30: YM2151 clock (32 bits)
Input clock rate in Hz for the YM2151 chip. A typical value is
3579545. It should be 0 if there us no YM2151 chip used.
For version 1.01 and earlier files, the YM2413 clock rate should be
used for the clock rate of the YM2151.
[VGM 1.50 additions:]
0x34: VGM data offset (32 bits)
Relative offset to VGM data stream.
If the VGM data starts at absolute offset 0x40, this will contain
value 0x0000000c. For versions prior to 1.50, it should be 0 and the
VGM data must start at offset 0x40.
0x38-0x3f: Reserved (must be zero)
Starting at the location specified by the VGM data offset (or, offset 0x40 for
file versions below 1.50) is found a sequence of commands containing
data
written to the chips or timing information. A command is one of:
0x4f dd : Game Gear PSG stereo, write dd to port 0x06
0x50 dd : PSG (SN76489/SN76496) write value dd
0x51 aa dd : YM2413, write value dd to register aa
0x52 aa dd : YM2612 port 0, write value dd to register aa
0x53 aa dd : YM2612 port 1, write value dd to register aa
0x54 aa dd : YM2151, write value dd to register aa
0x61 nn nn : Wait n samples, n can range from 0 to 65535 (approx 1.49
seconds). Longer pauses than this are represented by multiple
wait commands.
0x62 : wait 735 samples (60th of a second), a shortcut for
0x61 0xdf 0x02
0x63 : wait 882 samples (50th of a second), a shortcut for
0x61 0x72 0x03
0x66 : end of sound data
0x67 ... : data block: see below
0x7n : wait n+1 samples, n can range from 0 to 15.
0x8n : YM2612 port 0 address 2A write from the data bank, then wait
n samples; n can range from 0 to 15. Note that the wait is n,
NOT n+1.
0xe0 dddddddd : seek to offset dddddddd (Intel byte order) in PCM data bank
Some ranges are reserved for future use, with different numbers of operands:
0x30..0x4e dd : one operand, reserved for future use
0x55..0x5f dd dd : two operands, reserved for future use
0xa0..0xbf dd dd : two operands, reserved for future use
0xc0..0xdf dd dd dd : three operands, reserved for future use
0xe1..0xff dd dd dd dd : four operands, reserved for future use
On encountering these, the correct number of bytes should be skipped.
Data blocks:
VGM command 0x67 specifies a data block. These are used to store large amounts
of data, which can be used in parallel with the normal VGM data stream. The
data block format is:
0x67 0x66 tt ss ss ss ss (data)
where:
0x67 = VGM command
0x66 = compatibility command to make older players stop parsing the stream
tt = data type
ss ss ss ss (32 bits) = size of data, in bytes
(data) = data, of size previously specified
Data blocks, if present, should be at the very start of the VGM data. However,
for future compatibility, players should be able to parse data blocks anywhere
in the stream, simply by skipping past them if their type is unknown.
The data block type specifies what type of data it contains. Currently defined
types are:
00 = YM2612 PCM data for use with associated commands
All unknown types must be skipped by the player.
History:
[1.00]
Initial public release by Dave
[1.01]
Rate value added by Maxim; 1.00 files are fully compatible
[1.10]
PSG white noise feedback and shift register width parameters added by Maxim,
with note on how to handle earlier version files.
Additional wait command added by Maxim with thanks to Steve Snake for the
suggestion.
1.01 files are fully compatible but 1.01 players might have problems
with 1.10 files, hence the 0.1 version change.
[1.50]
VGM data offset added to header by Maxim.
Data block support added by blargg, to allow for better handling of YM2612 PCM
data.
Both of these changes have the potential to cause problems, but are really good
changes, so the version number has been increased all the way to 1.50.
