Archive for November, 2006

Final info about WMV3/VC-1 variants.

Thursday, November 30th, 2006

Known fourccs:

  • WMV3
  • WMVP
  • WVP2
  • WMVA
  • WVC1

Known meaning of flags:

  • RES_SM: really that’s two flags, RES_SM&2 indicated 411 interlaced mode and RES_SM&1 indicates sprite mode(or so it seems). These flags are mostly used by WMVP and WVP2
  • RES_X8: I-frames may be packed with X8 algo. This also means that each I-frame has additional bit in frame header signalling if current frame should be encoded with X8 or with standard encoding scheme. Used in WMV3 Complex Profile.
  • RES_FASTTX: still unknown, somehow interferes with motion compensation (at least it does not affect bitstream)
  • RES_TRANSTAB: each macroblock should have its own DC/AC table index, not one global stored in the frame header.
  • RES_RTM: Old version of WMV3 with different P-frame coding mode

X8 frames use their own Huffman codes (code lengths are stored as nibbles somewhere in bitstream) and also blocks looks like to be decoded in this way:

for(y=0;y

for(x=0;x< mb_width*2;x++){

decode luma block

if( x & y & 1)

decode both chroma blocks

}

}

Some news

Wednesday, November 29th, 2006

Ever heard of codec with fourcc WMVP? That is another Windows Media variant designed for slideshows, video albums, ets. Why I have got interested in it? WMV3 Complex Profile (aka Ye Olde Undocumented and Incompatible Advanced Profile) uses exactly the same coding method to store I-frames when flag RES_X8 is set (if it is not set then VC-1 Main Profile decoder may decode that movies).

While standard decoder output mostly garbage, some blocks are decoded correctly thus I hope it’ll be possible to add support for both WMVP and WMV3 CP.

Fraps: path of trial and error

Sunday, November 5th, 2006

I’ve just committed fully working (I hope) support for newer Fraps videos. While RE’ing that stuff I made two big mistakes: misunderstood bit reader to read only 31 bits from 32-bit word (which is not correct) and that Fraps version 4 is not identical to Fraps version 2. All of these is corrected now.

And now is a new category that Mike forgot to add to MultimediaWiki (hint, hint).

Supported screen capture codecs:

  • TechSmith codec (aka Ensharpen)
  • VMWare VMnc
  • DosBox ZMBV
  • Fraps
  • CamStudio

Unsupported screen capture codecs:

  • M$ Screen codecs MSS1 and MSS2
  • MSU Screen Capture Lossless Codec (SCLS)

Interesting – all those unsupported codecs use arithmetic coding (and as I suspect don’t work with palletized¬† images).