PAK (Metroid Prime)

The .pak format in Metroid Prime is a fairly simple packfile format; files are stored with a 32-bit file ID, and can optionally be compressed with zlib (Metroid Prime) or LZO1X-999 (Metroid Prime 2). The assets in a pak are split into two groups: named resources and dependencies. In general, only named resources are accessed directly by the game; the rest are dependencies of the named resources, and are accessed indirectly in the process of parsing those files.

Note that the Metroid Prime 3 E3 prototype uses this pak format as well, but has 64-bit file IDs. This is the only difference; the version number isn't even any different, so there isn't an easy way to check for this variation of the format.

Format

Header

There's a short 8-byte header; most of it is unknown, but they're always the same values.

Offset	Size	Description
0x0	2	Unknown; always 0x3. The game ignores this value.
0x2	2	Version number. Always 0x5.
0x4	4	Unknown; always 0.

Named Resources

The named resource table lists files that the game has direct access to. On world paks, this will generally only contain the MLVL file; in other paks, this table is usually quite a bit larger. Note that in non-world paks, the names are hardcoded and are how the game knows where to find the files; if you repack, you need to make sure you keep the names the same.

This section of the file begins with a 32-bit named resource count, followed by a table.

Offset	Size	Description
0x0	4	Four-character file type tag.
0x4	4	File ID.
0x8	4	Name length (NL)
0xC	NL	Name; not zero-terminated
0xC + NL	End of entry

Resource Table

This could be considered the main table of contents of the pak. This table begins with a 32-bit resource count, followed by one entry per file; each entry is 0x14 bytes large.

Offset	Size	Description
0x0	4	Compression flag; this will either be 0 or 1, with 1 denoting a compressed file.
0x4	4	Four-character file type tag.
0x8	4	File ID
0xC	4	Offset
0x10	4	Size
0x14	End of entry