[XviD-devel] question about gmc

[skal]

	Re,

On Fri, 2003-03-07 at 15:15, Christoph Lampert wrote:
> Hi,
> 
> On Fri, 7 Mar 2003, Radek Czyz wrote:
> > > Also, we don't use the result of GME as predictor, if the
> > > result is translational-only (GMC is switched off, then) and that we
> > > really should.
> > 
> > ...and that puts me back to not-understanding part of the universe..
> > We can't use the result of GME as predictor because we do GME later.
> 
> Again, I meant of previous frame.

	yup, my idea was average 'GMC' vector from previous frame
	(even if it was only 'estimated' with GMC, but not actually
	coded with GMC)...
	According to some rough tests I made, it's interesting for
	for camera shots (with big zoom:). Conversely, it's rather 
	useless for synthetic scenes like 'look at my raytraced fly-by'
	where the camera rotates like hell 
> 
> > I'll go to sleep now. The best thing to do ;))))
> 
> > Ah, just a simple suggestion/question. In B-frames, we do ME first
> > and coding later (just like in pframes). Is there something which
> > would stop us from doing it one by one? (ME->MC->coding; repeat)?
> > 
> > It could be a bit faster - MC data still in cache after ME.
> 
> There are two approached in a clash:
> 
> a) Do everything macroblock based, 
>    ME for a (macro)block, MC for the block, DCT for the block, 
>    bitstream encoding etc. for the block, then start with next block
> 
> b) Do everything framebased, 
>    ME for all blocks, MC for all blocks, DCT for all blocks etc. 
> 
> The advantage of a) is speed. Everything is as localized as possible, 
> so you can reuse cached data. 
> 
> The advantage of b) is "more information". You can reuse data from the
> previous step for the next. This is useful for everything "adaptive",
> e.g. adative quantization might want to use ME information of _all_
> blocks before decising on a quantizer for _any_ block. 
> 
	there's also the b/p late decision: a queue of potentially
	b-coded (except the last, p-coded) frames is maintained,
	and the bitstream syntax will be different when the final
	decision is made...

	bye,
		Skal