Kostya's Boring Codec World

RTMP client seems to work fine, RTMP support in FFserver is not that close, so I work on REing some codec which seems to be rather widespread in games.

OK, now to technical details. ‘Lossless’ coefficient coding is similar but a bit more complicated.

For each 8×8 block there is 7-bit number specifying number of masks to read (mask = part of the coefficient), slightly resembling progressive JPEG coding; coefficient value may be composed from several masks, high bits are decoded first. Decoding continues until all masks are read.

Coding method is not that comprehensible though: there is list of start coefficient and modes, so decoding iterates over this list and performs some action depending on mode. Have I mentioned that aforementioned list may change during operation?

And here’s decoding algorithm (if I got it right):


mask = 1 < < get_bits(3) iterate over already decoded coefficients, if read bit = 1 then add mask to the coefficient iterate over list of modes until end is reached, if (coef,mode)==(0,0) or read bit = 0 then skip current entry:   mode = 0:    set current entry to (cur_coef+4; mode = 1)    for(i=0;i<4;i++, cur_coef++){     if(get_bit()) prepend list with (cur_coef, mode = 3)     else coeffs[cur_coef] = get_bit() ? -mask : mask;    }   mode = 1:    set current entry to (cur_coef; mode = 2)    append (cur_coef+4; mode = 2), (cur_coef+8; mode = 2), (cur_coef+12; mode = 2) to the list   mode = 2:    set current entry to (0; mode = 0)    for(i=0;i<4;i++, cur_coef++){     if(get_bit()) prepend list with (cur_coef, mode = 3)     else coeffs[cur_coef] = get_bit() ? -mask : mask;    }   mode = 3:    coeffs[cur_coef] = get_bit() ? -mask : mask;

This entry was posted on Saturday, August 29th, 2009 at 6:19 am and is filed under Bink, Game Video. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.