Adlib Tracker II pattern
.a2p files are patterns created by Adlib Tracker II.
The file format consists of two parts - a header containing authenticity information such as CRC and the format version, which is ended by one or more values containing the length of the second section. The second section contains the compressed data.
The compression algorithm used for the second part can be identified from the format version. Versions 1 & 5 are compressed with SixPack; 2 & 6 with LZW; 3 & 7 with LZSS. Versions 4 & 8 use no compression.