Microsoft Screen Codec

Also known as Windows Media Screen Codec.

• FourCCs: MSS1, MSS2, MSA1
• Samples:
  • http://samples.mplayerhq.hu/V-codecs/MSS1/
  • http://samples.mplayerhq.hu/V-codecs/MSS2/

MSA1 is created by Live Meeting 2007

Some details about format

Both MSS1 and MSS2 are quite close (thus are decoded with single decoder). They employ arithmetic coding - real one, with probability coding. This coding is used with several adaptive models, which look a bit like PPM.

Extradata format

(for some reason, data in .wmv is stored in big-endian order)

 4- 7  header length
 8-11  major version
12-15  minor version
16-19  display width
20-23  display height
24-27  coded width
28-31  coded height
32-35  frames per second (float)
36-39  bitrate
40-43  max lead time (float)
44-47  max lag time
48-51  max seek time
52-55  nFreeColors
56-... palette (256 RGB triplets)