- FOURCCs: VMnc
- Preferred container: AVI
- Company: VMware
- Samples: http://samples.mplayerhq.hu/V-codecs/VMnc/
The VMware Workstation (a commercial x86 machine emulator) can record sessions using this codec. Read the brief story behind the reverse engineering of this codec. It is suspected to be a lossless codec.
Cursory investigation details in this blog post: http://codecs.multimedia.cx/?p=9
Basically it is just a recorded session of the RFB protocol, which is used by VNC. Probably a VNC server is running on the virtual machine, while a client outside records it.
Bitstream structure (this resembles the VNC FrameBufferUpdate format), everything is big-endian ordered:
8bit message type 8bit padding 16bit number of rectangles coded
For each rectangle:
16bit x position 16bit y position 16bit coded width 16bit coded height 32bit encoding type
Encoding type might be 0 to 5 as found in the RFB Protocol specification, but current samples reveal that type 5 (HexTile) is the most common and sometimes type 0 (Raw) occur.
RFB encoding types
- 0x0 Raw block
width * height * depth bits of raw picture
- 0x1 copy rectangle from x,y in previous frame
16bit x position in previous frame 16bit y position in previous frame
- 0x2 RRE (rise-and-run length encoding) encoded data
- 0x4 CoRRE encoded data
- 0x5 Hextile encoded data
WMVi (ServerInitialisation structure)
VMware adds special encoding types, abusing the whole structure. VNC ServerInitialisation is stored in the above format with encoding type set to WMVi.
8bit bits per sample 8bit depth 8bit color stored in big endian order 8bit this is TrueColor (i.e. not requring palette) 16bits maximum value of red 16bits maximum value of green 16bits maximum value of blue 8bit red value shift 8bit green value shift 8bit blue value shift 24bit padding
However, this is also signaled right in the AVI header. This block occurs only in keyframes.
There are other unknown encoding types which were not yet descrambled:
WMVd (cursor data)
This block contains cursor bits and mask where cursor hot spot is defined by x,y position of image.
16bit unknown width*height*depth bits - cursor bits width*height*depth bits - cursor mask
Cursor should be drawn by simple code:
dst[i] = (dst[i] & bits[i]) ^ mask[i];
WMVf (cursor position)
This block is empty and x,y position defines the new position of cursor hot spot (NOT the top left corner of cursor image).
Still unknown blocks
2 bytes of payload (always 0x00 0x01?)
3*2 bytes of payload.
2 or 3 bytes of payload.