Kostya's Boring Codec World

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

}

}

This entry was posted on Thursday, November 30th, 2006 at 1:45 am and is filed under VC-1. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.