[x264-devel] PSNR vs the distance of reference frame

[Loren Merritt]

On Tue, 29 Jun 2010, john sisi wrote:

> I performed an experiment using x264 to find the effect of using
> different reference frames on the PSNR performance. I got a somehow
> weird result: it seems that the PSNR goes up (by about 0.2dB on
> Foreman CIF @256kbps) as the distance to the reference frame is
> increased (from 3 to 15).
>
> I set the number of reference frame to 15 using "--ref 15" and I
> changed the code such that I was able to select only one of these 15
> reference frames for encoding the frames. For example, in
> "x264_mb_analyse_inter_p16x16" I set "i_ref" to 5 just before
> "REF_COST( 0, i_ref )" to use only the 6th reference frame. I applied
> the same change on the other relevant functions like
> "x264_mb_analyse_inter_p16x8".

I don't know how exactly you broke analysis, but you shouldn't have to 
modify analysis at all. Your change can be accomplished in 
x264_reference_build_list alone.

--Loren Merritt