AST file

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AST files contain PCM16 (16-bit signed) sound data. They're used in Super Mario Galaxy for musics, and possibly in other games.

They contain an header, followed by BLCK chunks which are divided in blocks.
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.

AST header

The header is 64 bytes long. Here's a description of it:

Offset Size Description
0x0000 4 "STRM" (0x5354524D)
0x0004 4 Size of all the BLCK chunks (size of the file minus 64)
0x0008 4 Unknown (0x00010010)
0x000C 2 Number of blocks per BLCK chunk
0x000E 2 Unknown (0xFFFF)
0x0010 4 Sampling rate in Hz (typically 0x7D00 = 32000 Hz)
0x0014 4 Unknown
0x0018 4 Loopstart position in samples, from beginning of BLCK chunk
0x001C 4 Unknown (typically same as entry 0x0014)
0x0020 4 Block size for the first chunk? (typically 0x2760)
0x0024 28 Unknown

BLCK chunks

The BLCK chunks directly follow the AST header. They contain a 32-byte header, followed by PCM16 sound data.
Here's a description of them:

Offset

(from beginning of BLCK chunk)

Size Description
0x0000 4 "BLCK" (0x424C434B)
0x0004 4 Block size (typically 0x2760)
0x0008 24 Padding (zero)
0x0020 variable PCM16 data blocks

The data is divided into blocks. The number of blocks is defined by entry 0x0004 in BLCK chunk header.
The length of each block is defined by entry 0x0020 in AST header.

WARNING: The PCM16 data is stored in BIG-ENDIAN! If you aren't working on the Wii, don't forget to byteswap each sample you read or your sound will be pure junk!
Note: there's sound data for one channel only. Stereo mixing is performed by the Wii's DSP.

AST file structure

Element Size
AST header 64 bytes
BLCK chunk header 32 bytes
PCM16 block 1 N
PCM16 block 2 N
...
PCM16 block N' N
BLCK chunk header 32 bytes
PCM16 block 1 N
PCM16 block 2 N
...
PCM16 block N' N
BLCK chunk header 32 bytes
...

Where:
- N is the number of blocks per BLCK chunk (entry 0x000C in AST header)
- N' is the block size (entry 0x0020 in AST header)