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Old 19th October 2009, 19:03   #16  |  Link
akupenguin
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Join Date: Sep 2004
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Slices can only end at macroblock boundaries, which is precisely the condition on which borders aren't too horribly inefficient anyway.
The number of bits wasted in waiting for cabac to readapt from coding "all skips" to coding real content, is less than the number of bits spent on a slice header. Because the border will be all skips, so it doesn't need to code any other type of token, so it doesn't contaminate any other part of the cabac model.
A new slice might possibly improve mv prediction along the top edge (which would otherwise use a constant 0 prediction due to the two neighbors with mv=0), and it would allow use of DC prediction for intra blocks there (which would otherwise average half of its neighbors from the black part). This doesn't do jack for the bottom border, since motionless skip blocks don't rely on neighbors even that much.

Quote:
Originally Posted by Shevach
Then compose a new video by concatenating raw data of the first excerpt and the second one.
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).

Last edited by akupenguin; 19th October 2009 at 19:12.
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