[x264-devel] Re: Motion Estimation in X264

[Mathieu Monnier]

> Weird, I thought you'd always need to use the reconstructed frame, as that's
> what the decoder will base it's prediction on. I thought errors would accumulate
> otherwise.

Indeed, but there's a difference between motion estimation, and actual 
encoding. You can very well search the motion between two non-encoded 
frames, then encode the frame with the found motion vectors and the 
actual reconstructed references. It may even be worthwhile at low 
bitrates when the frames get really distorted by the encoding process. 
I'm especially thinking of the mpeg2/4 blocking at high quantizer, which 
tends to bork motion estimation. AVC, in that regards, suffer much less 
thanks to the inloop deblocking.

> If you are encoding with high quality and frequent I-frames, I guess
> you could get away with using the original picture for reference.  It
> would save a few cycles in the encoder avoiding the reconstruction
> step.

I hope nobody is that desperate for speed. If so, then let him use ASP, 
instead of crippling a codec :)

Regards,

Mathieu

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