ViewQuest VQC

• FOURCCs: VQC1, VQC2, VQS1, VQS2
• Company: VideoQuest Technologies Inc
• Samples: ???

There seem to be four different codec IDs that somewhat differ in frame header format but they all employ the same compression which is splitting frame into stripes, applying 1-D transform which looks like LGT 5/3 wavelet transform, and coding result in 32-bit chunks using fixed quantisation and variable-length codes.

Data Format

After the frame header the actual data follows. Bitstream is coded MSB.

Data is coded as 32-byte chunks with the following scheme: first two bytes are transmitted as is and the rest is coded with the following codes.

 10 - end of chunk
 00 - output 0
 0100 - skip 3 entries
 0101 - skip 4 entries
 0110 - skip 5 entries
 0111 - skip 6 entries
 1100 - output 1
 1101 - output -1
 111000 - output 2
 111001 - output 3
 111010 - output 4
 111011 - signed 8-bit value follows, 0=end of data
 111100 - output -2
 111101 - output -3
 111110 - output -4
 111111 - signed 6-bit value follows

After that values are expanded using fixed quantisation tables and three-pass wavelet transform is applied.

Transform:

 s0 = y0[0] + (y1[0] >> 1);
 for (i = 0; i < size / 2 - 1; i++) {
   dst[i*2]     = s0;
   s0 = y0[i + 1] + ((y1[i] + y1[i + 1]) >> 1);
   dst[i*2 + 1] = ((dst[i*2] + s0) >> 1) - 2 * y1[i];
 }
 dst[width - 2] = s0;
 dst[width - 1] = y0[size / 2 - 1] + ((y1[width / 2 - 1] - 2 * y1[size / 2 - 2]) >> 2) - y1[size / 2 - 2];