All files share the same header:
DWORD magic // 'DXT5'
DWORD format? // 'RLES'
DWORD unknown // Always 0x00020004 (could be flags? or 2 WORDs)
DWORD unknown // Always 0x0B000000 (=11 in decimal)
DWORD unknown2 // Always 0x18010000 (=280 in decimal)
DWORD count?