Zork PMV

• Extensions: PMV
• Decoder: [1]

This is a format used in MADE engine game Return to Zork.

Container format

Data is organised into chunks with 32-bit payload length following the 4-byte chunk identifier:

• MOVE - root chunk
• MHED - header
• MFRM - frame chunk

Header contents:

2 bytes - frame delay (1000 / fps)
4 bytes - always zero?
2 bytes - number of frames
4 bytes - always zero?
2 bytes - sample rate
44 bytes - unknown 16-bit words
768 bytes - palette

Frame chunk header:

8 bytes - unknown
4 bytes - audio data offset (from the chunk ID, not from payload start)
4 bytes - image data offset
4 bytes - palette data offset (if present)

Audio part header:

4 bytes - unknown
2 bytes - single chunk size in samples
2 bytes - number of chunks

Image part header:

8 bytes - unknown
2 bytes - width
2 bytes - height
2 bytes - block type data offset (from the image part start)
2 bytes - unknown
2 bytes - pixel data offset
2 bytes - unknown
2 bytes - mask data offset
2 bytes - stride

Palette data stored in form of updates telling at which offset and how many colours to update:

1 byte - number of colours
1 byte - start colour (255, 255 means end of palette update data)
N*3 bytes - colour data

Video compression

Video is compressed using vector quantisation for 4x4 blocks with various data elements grouped together (command/block type, raw pixels, pixel masks).

Block types are stored in two-bit variables:

• 0 - raw block (read 16 pixels from the pixel data part)
• 1 - two-colour block (read 2 pixels from the pixel data part and 16-bit mask from the mask data part, arrange pixels using mask)
• 2 - four-colour block (read 4 pixels and 32-bit mask for sixteen 2-bit colour indices)
• 3 - skipped block

Audio compression

Each audio chunk starts with a byte telling how it should be decoded:

• bits 0-3 - compression type
• bits 6-7 - modifier (1 - decode every odd sample, linearly interpolate every even sample from them, 2 - decode and use for interpolation every fourth sample)

Compression types:

• 0 - zero output
• 1 - no change
• 2-4 - read 2/4/16 U8 samples to delta buffer, for every sample read 1/2/4-bit index, use corresponding delta value to update the previous sample with clipping
• 5 - raw unsigned 8-bit audio data