Quote:
Originally Posted by akupenguin
That mixes a change in entropy coding with a change in motion interpolation. mvs that used to point off the left or right edge of the frame (and thus get extrapolated samples), now point into the other video (and thus get much worse values).
|
The question is how from the mixture extracts the very impact of entropy change?
Let's consider a P-frame with width 64x16 pixels where all MBs at each even row are non-skip while all MBs at each odd row are skip.
In such case for mb_skip_flag syntax element only one context model with number 12 is always selected since left MB is always skip/non-skip and top is always non-skip/skip.
Upon an encoder finishes an even row the context model #12 contains LPS=1 (least probable symbol) with the probability 0.01875 (the minimal probability in CABAC).
Now the encoder starts to process the next MB row (odd row) where all syntax elements to code are mb_skip_flag and end_of_slice. The number of bits are generated for mb_skip_flag of the first MB is 6-7 bits. After 64 MBs mb_skip_flag is coded with ~1 bit. Thus ~2-3 extra bits are produced in average for coding of mb_skip_flags.
The above example shows how the change of entropy affects on total output size.