Karl Morton's Video Codec

• FourCC: KMVC
• Samples: http://www.mplayerhq.hu/MPlayer/samples/V-codecs/KMVC/

KMVC is used on various Worms PC games.

Common details

This codec operates on 8x8 or 16x16 blocks in 256 colors mode. This codec is also employs exotic bitstream reading: actually you need to read byte and when it's exhausted, read another byte, so flags and other data are very mixed.

Frame structure

Frame consists of the next parts: header byte, palette chunk (if needed), compressed blocks.

Header byte may have this bits set:

KPxx MMMM
K - is keyframe
P - palette is present
xx - unknown bits
MMMM - compression method (only methods 3 and 4 are known)

Details for palette chunk are still unknown. Compressed blocks are decoded with given method until frame is fully decoded.

Method 3 for block 8x8

This is method used in intraframes:

 if(!getbit()){
   val = getbyte();
   fill block 8x8 with val;
 } else {
   for all subblocks 4x4 {
     if(!getbit()){
       if(!getbit()){
         val = getbyte();
         fill block 4x4 with given val;
       } else {
         val = getbyte();
         mx = val & 0xF;
         my = val >> 4;
         copy block 4x4 from offset (-mx, -my)
       }
     } else {
       for all subblocks 2x2 (in subblock 4x4) {
         if(!getbit()){
           if(!getbit()){
             val = getbyte();
             fill block 2x2 with given val;
           } else {
             val = getbyte();
             mx = val & 0xF;
             my = val >> 4;
             copy block 2x2 from offset (-mx, -my)
           }
         } else {
           block[0,0] = getbyte();
           block[0,1] = getbyte();
           block[1,0] = getbyte();
           block[1,1] = getbyte();
         }
       }
     }
   }
 }

Method 4 for block 8x8

[TODO]

Method 3 for block 16x16

[TODO]

Method 4 for block 16x16

[TODO]