BRSTM files store sound data. They're used in Mario Kart Wii and possibly other games.
They contain an header, followed by a HEAD chunk, a 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.
The header is 64 bytes long.
|0x0008||4||Size of the whole file|
|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|