[XviD-devel] Mode decision

[Christoph Lampert]

Hi,

from the logfile which a modified version of syskins mode decision
generates, it seems clear to me, that the decision INTER/INTER4V is the
crucial part. In foreman and miss_america, INTRA blocks are hardly
present, but still BITS-decision manages to significanty lower bitrate. 

I plotted the "sad16 / sad8"-values of those blocks who were classified 
INTER using bitcount (green) and those who classified INTER4V (red).
The blue line is approximately our current decision 
method: sad16<sum_of_sad8 (the extra penalty is only 2*quant, it would 
hardly be visible in the plot). 

What you can see is that we are _very_ conservative when it comes to
choosing INTER4V. All "real" INTER are classified correctly, but a vast
number of "real" INTER4V is classified as INTER. 

You can also see, that using current sad16/sad8, no good decision
boundaries are possible at all, because the area completely overlap. 

What you can't see, is how much a misclassification of INTER->INTER4V
or vice versa would cost in extra bits. 
And you also cannot see that there are hardly any real INTER4V blocks
with sad16 below 600. So maybe this would be a way to speed things up, 
simply not doing inter4v for those.

But of course I only tested one clip so far. 

gruel 
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