[x264-devel] Re: Motion Compensation Routines

[rupert.mish at comcast.net]

Is the MC algo in x264 published somewhere? Does it use rate distortion costs?

Thanks,
- Rupert

 -------------- Original message ----------------------
From: Loren Merritt <lorenm at u.washington.edu>
> On Thu, 23 Nov 2006, rupert.mish at comcast.net wrote:
> 
> > I plan to try out a motion prediction algorithm.  I'd like to know what 
> > routines to start with and what data structures to access for the frames 
> > and blocks? Just to get a handle, I'll probably have to come back with 
> > the specifics. I'd appreciate getting help from you folks.
> 
> All of the following is in common/mc.c
> 
> x264's motion compensation framework includes some optimizations that are 
> specific to h264. h264's motion compensation first does a 6tap filter to 
> produce halfpel samples from pixels, and then each qpel sample is an 
> average of two halfpel samples. So x264 does the same: 6tap filter for all 
> 3 halfpel offsets and store the results, and then each later request for a 
> motion-compensated block just computes the halfpel-to-qpel step if 
> necessary, or returns a pointer to one of the pre-computed halfpel planes.
> 
> If your proposed mc algo fits in the same framework, then the way to 
> implement it is: modify mc_hh, mc_hv, mc_hc to do your halfpel 
> interpolation, and modify mc_luma and get_ref to do your halfpel-to-qpel 
> interpolation.
> If not: ignore the halfpel step. mc_luma should perform the whole 
> interpolation process, using only src[0] (which is the original pixels) 
> not src[1..3] (which are the halfpel planes). get_ref should just call 
> mc_luma.
> 
> Chroma doesn't follow that framework, so motion_compensation_chroma just 
> takes some pixels and returns some interpolated samples.
> 
> In all cases, the mc functions are given a pointer to the pixels they're 
> supposed to work with, so you don't have to worry about where the pixels 
> are stored.
> 
> --Loren Merritt
> 
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