BRSTM file

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BRSTM files contain ADPCM sound data. They are used for music in some games, such as Super Smash Bros. Brawl and Mario Kart Wii.

They contain a header, followed by a HEAD chunk, an ADPC chunk and a DATA chunk.
All the data in those files are big-endian, except where mentioned.
All the offsets are absolute (from begining of file), except where mentioned.
All the sizes are in bytes, except where mentioned.

BRSTM header

The header is 64 bytes long.

Offset Size Description
0x0000 4 "RSTM" (0x5253544D)
0x0004 2 Byte Order Mark (BOM), usually 0xFE 0xFF for big endian.
0x0006 1 Major version
0x0007 1 Minor version
0x0008 4 Size of the whole file
0x000C 2 Header size
0x000E 2 Number of chunks
0x0010 4 Offset to HEAD chunk
0x0014 4 Size of HEAD chunk
0x0018 4 Offset to ADPC chunk
0x001C 4 Size of ADPC chunk
0x0020 4 Offset to DATA chunk
0x0024 4 Size of DATA chunk
0x0028 24 Unknown/Padding (zero)

HEAD chunk

The HEAD chunk contains information about the brstm file, including sample rate, loop information, volume, panning, and information on each of the ADPCM streams.

This chunk contains 3 internal parts.
Part 1 contains general information about the file such as loop information, sample rate, and data needed to deinterleave the audio stream.
Part 2 defines the tracks in the file, and contains volume and panning information for each of them.
Part 3 contains the information needed to decode the ADPCM audio, including the ADPCM coefficients, and history samples.

Any offsets in the HEAD chunk are relative to offset 0x08 in the HEAD chunk unless otherwise noted.

HEAD chunk header

Offset Size Description
0x0000 4 "HEAD" (0x48454144)
0x0004 4 Length of entire HEAD section.
0x0008 4 Marker? (0x01000000)
0x000C 4 Offset to HEAD chunk part 1
0x0010 4 Marker? (0x01000000)
0x0014 4 Offset to HEAD chunk part 2
0x0018 4 Marker? (0x01000000)
0x001C 4 Offset to HEAD chunk part 3

HEAD chunk part 1
This part is 0x34 bytes long

Offset Size Description
0x0000 1 Codec:

0 - 8-bit PCM
1 - 16-bit PCM
2 - 4-bit ADPCM

0x0001 1 Loop flag
0x0002 1 Number of channels
0x0003 0 Padding? (0x00)
0x0004 2 Sample rate
0x0006 2 Padding? (0x00)
0x0008 4 Loop start in samples
0x000C 4 Total sample count
0x0010 4 Absolute offset to the beginning of the ADPCM data.

Note that this is not the beginning of the DATA chunk.

0x0014 4 Total block count.

The total number of interlaced blocks in the ADPCM data. This count includes the final block.

0x0018 4 Block Size in bytes.
0x001C 4 Samples per block.
0x0020 4 Size of the final block without padding in bytes
0x0024 4 Samples in the final block.
0x0028 4 Size of the final block with padding in bytes
0x002C 4 Samples per entry in the ADPC table
0x0030 4 Bits per sample? (0x04 for 4-bit ADPCM)

ADPC chunk

The ADPC chunk is typically 1216 bytes long. It seems to contain some other ADPCM table.

DATA chunk

The DATA chunk contains ADPCM sound data.