[x264-devel] Re: H.264 motion vector predictor?

[Juliano Pillati]

please, send me url or to list your "MV predictor" ?
I like read too :-)

Juliano

Tuukka Toivonen wrote:

> I'm trying to understand how the motion vector prediction is done in 
> x264 and H.264 in general. I've looked from various places but it's 
> still obscure.
>
> As far as I know, the MV predictor is obtained as median of MVs of 
> (sub)partitions left, above, and above left of the current 
> (sub)partition. For 16x8 and 8x16 partitions it's different, but I 
> think I understand that case too.
>
> Let's suppose that a macroblock (MB) is divided into four 8x8 partitions,
> and the upper-right partition is further divided into four 4x4 
> partitions.
>
> According to my understanding, when motion estimation is performed for 
> the
> lower right 8x8 partition, one of the MVs from which the median is 
> computed is the lower-left 4x4 subpartition of the top-right partition 
> of the same macroblock. But this is impossible, because x264 estimate 
> the MV for that
> subpartition later than the MV for the lower-right partition.
>
> (I assume here the one uses SAD+lambda*bits(mv) for MV selection, in
> which case it is necessary to know MV predictor for a (sub)partition
> when performing motion estimation for it)
>
> Can anyone point to a tutorial which describes how the MV predictor
> is exactly computed?
>
> There used to be a nice explanation at
> http://www.vcodex.com/h264.html
> but it was removed from a later version
> (I still have the original, but I'm not sure if it is exactly correct).
>
> Some nice figures: here's the order in which JM does motion
> estimation for the (sub)partitions:
> http://www.ee.oulu.fi/~tuukkat/tmp/multisize.png
> Here's the order for x264:
> http://www.ee.oulu.fi/~tuukkat/tmp/multisize-x264.png
>

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