Cydonia Paco

• Company: Aneiva Interactive, Inc.
• Extension: pac

This is a format used in Cydonia game and not related to PACo.

The file consists of 4-byte magic Paco, initialisation chunk and one or more data chunks. Chunks starti with single byte for chunk type and 32-bit little-endian chunk size.

Known chunk types:

• 1 - initialisation chunk
• 2 and 3 - video frame
• 4 - new palette data (may be shorter than 768 in theory)
• 5 - audio data
• 20 - silence (32-bit payload tells silence length)
• 21 - something audio-related
• 30-35 - some frame management opcodes
• 50 - unknown
• 60-61 - related to fading?

Initialisation chunk should be 7 bytes long:

 16 bits - video width
 16 bits - video height
 16 bits - number of frames
  8 bits - audio present flag

Video is compressed using LZ77-based scheme for both frame types with small differences in codewords and ways to copy previous frame data (one uses lines, another one uses blocks).