AGSC (File Format)

AGSC is the sound format for Metroid Prime and Metroid Prime 2: Echoes. According to the debug maps in Metroid Prime, there are references to various "classes", with one of them controlling audio in the map, known as AudioGroupSet. So presumably, AGSC is an abbreviation for Audio Group Set Class.

The audio codec used for AGSC is the standard Gamecube DSP ADPCM codec, as described in the Gamecube SDK.

Format

There are two types of AGSC files: those found in Metroid Prime, and a slightly different version in Metroid Prime 2.

AGSC (Metroid Prime 1)

Header

Offset	Size	Description
0x0	7	Audio Directory. Always 'Audio/.' (0x417564696F2F00)
0x7	Varies	Audio Subdirectory This tells us what sounds are in the file (for example, "metroid" or "weapons"). After the subdirectory name, there is also a 0x00 byte that follows for padding.
Start of offset chunks table Each chunk is in order, each one starting with its size value, 32 bytes.
End of header After all the chunk offsets are listed, the header chunk terminates with 0xFFFFFFFF.