[XviD-devel] trellis questions

skal skal at planet-d.net
Sat Sep 11 07:33:27 CEST 2004


	Hi Syskin and all,

On Sat, 2004-09-04 at 14:00, Radek Czyz wrote:
> Hi everyone,
> 
> I'm still breaking trellis search :) and I have a question:
> 
> There is a code
> 
> 	/* source (w/ CBP penalty) */
> 	Run_Costs[-1] = 2<<TL_SHIFT;
> 
> As far as I understand, it's an approximation of CBP cost - but I have 
> absolutely no idea how it works... so, how?

	It's really a rough approximation, based on few
	experimentations. This pseudo-cost associated to
	the node -1 is just an artificial barrier to overcome
	when any coeff gets coded at all.

	
> Also, how do I change the code if the block is initially empty and I'm 
> running trellis anyway? (IF I do that. if.)
> 
> Or maybe CBP is just not taken into account?

	Sure, the real CBP is not taken into account.
	We only evaluate the save for not coding a
	block as 2 bits/block, on average.

	(maybe the real value is a little lower, btw).

	bye!
Skal




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