PMM

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The game Krazy Ivan uses multimedia files with the extension .pmm. Carries encoded 15-bit video along with PCM or DPCM (never used) audio track.

Contents

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File Format

File structure follows general RIFF format, but uses custom chunk names. All numbers are little endian.

File begins with 4 * 3 bytes catalog header: 

u32 fourcc     -- "PIFF"
u32 filesize   -- not including fourcc and filesize fields
u32 filetype   -- "PXMT" /PXM Type?/

followed by chunks: 

u32 fourcc             -- chunk FOURCC
u32 chunksize          -- not including fourcc and chunksize fields
u8  payload[chunksize] -- chunk data
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PXMH chunk

/PXM Header?/ Carries general movie information. 

u16 unknown0
u16 flags
u16 width           -- frame width in blocks
u16 height          -- frame height in blocks
u16 bwidth          -- block width (always 8)
u16 bheight         -- block height (always 8)
u16 framerate
u16 numframes
u32 maxframe        -- size of the largest BODY chunk
u8  descrition[32]
u16 audiofreq
u8  audiotype       -- audio compression format
u8  audiochnl
...                 -- the rest is unknown/unused
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CPAL

8-bit palette. Obsolete.

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MPAL

Palette? Obsolete.

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BODY

Contains encoded vide frame. See below.

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AUDO

Contains audio fragment. See below.

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Video Compression

Vide is encoded as a series of bwidth x bheight blocks (typically, 8x8), which may further be divided in to smaller blocks. Pixel format is 15-bit RGB.

Video payload format: 

 u16  codetable_ofs   -- offset of code table bitstream (inside the chunk)
 u16  pixels_ofs      -- offsets of pixels data (inside the chunk)
 ...
 u8   codetable[]     -- bitstream data, read bits from the lowest of each byte
 u8   pixels[]        -- encoded pixel data (bytes)

Compression is based on selective pixel color components change within the block. To decode single block:

1. Initialize last_pixel to 0
2. Read the 3-bits color_mask value. This is a bit mask, indicates which pixel components will be changed (bit 0 - Red, 1 - Green, 2 - Blue). Zero value indicates the whole block is unchanged.
3. Read next bit. If bit is zero, decode pixel and use it to draw the whole (sub)block; otherwise
4. If subblock size is 2, decode each pixel of subblock and draw it; otherwise
5. Split the (sub)block on to 4 equial subblocks and process recursively from step 3 (left-right-top-bottom.)


DecodePixel operates as follows:

1. Read next 8-bits pixel_data (from pixels[])
2. If high bit of pixel_data is set, pixel value is the next entry of pixels[] (lower part) combined with 7 bits of pixel_data (upper part.); otherwise
3. Color_index = value in bits 5-6 of pixel_data (0 - Blue, 1 - Green, 2 - Red, 3 - Skip), color_value = bits 0-4 of pixel_data. If color_index is Skip, assume pixel value is last_pixel. Otherwise, for each color component selected by color_mask, set it to color_value if it's the same component as specified by color_index, or if color_mask indicates no change of color_index component (this case is used to change two components at once.) Reuse all untouched components from last_pixel.
4. Set last_pixel to newly decoded pixel value.

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Audio Compression

According to audiotype field, audio can be stored in the following formats:

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Type 0 - PCM16

Raw 16-bit PCM samples.

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Type 1 - Packed PCM16

Only high 8 bits of 16-bits sample stored. I.e. DecodedSample = data << 8.

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Type 2 - DPCM

Decode a sample using the following DPCM table: 

-32767,-30191,-27818,-25631,-23617,-21760,-20050,-18474,-17021,-15683,-14451,-13315,-12268,-11304,-10415, -9596,
 -8842, -8147, -7506, -6916, -6373, -5872, -5410, -4985, -4593, -4232, -3899, -3593, -3310, -3050, -2810, -2589,
 -2386, -2198, -2025, -1866, -1719, -1584, -1460, -1345, -1239, -1142, -1052,  -969,  -893,  -823,  -758,  -698,
  -643,  -593,  -546,  -503,  -464,  -427,  -393,  -363,  -334,  -308,  -283,  -261,  -241,  -222,  -204,  -188,
  -173,  -160,  -147,  -135,  -125,  -115,  -106,   -97,   -90,   -83,   -76,   -70,   -65,   -59,   -55,   -50,
   -46,   -43,   -39,   -36,   -33,   -31,   -28,   -26,   -24,   -22,   -20,   -19,   -17,   -16,   -14,   -13,
   -12,   -11,   -10,    -9,    -9,    -8,    -7,    -7,    -6,    -6,    -5,    -5,    -4,    -4,    -4,    -3,
    -3,    -3,    -2,    -2,    -2,    -2,    -2,    -1,    -1,    -1,    -1,    -1,    -1,    -1,    -1,     0,
     1,     1,     1,     1,     1,     1,     1,     1,     2,     2,     2,     2,     2,     3,     3,     3,
     4,     4,     4,     5,     5,     6,     6,     7,     7,     8,     9,     9,    10,    11,    12,    13,
    14,    16,    17,    19,    20,    22,    24,    26,    28,    31,    33,    36,    39,    43,    46,    50,
    55,    59,    65,    70,    76,    83,    90,    97,   106,   115,   125,   135,   147,   160,   173,   188,
   204,   222,   241,   261,   283,   308,   334,   363,   393,   427,   464,   503,   546,   593,   643,   698,
   758,   823,   893,   969,  1052,  1142,  1239,  1345,  1460,  1584,  1719,  1866,  2025,  2198,  2386,  2589,
  2810,  3050,  3310,  3593,  3899,  4232,  4593,  4985,  5410,  5872,  6373,  6916,  7506,  8147,  8842,  9596,
 10415, 11304, 12268, 13315, 14451, 15683, 17021, 18474, 20050, 21760, 23617, 25631, 27818, 30191, 32767, 32767
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