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

[john sisi]

Thanks a lot Loren, just to make sure, could you please tell me what
exactly should I change in "x264_reference_build_list alone"? I want
to just enforce the encoder to use say 5th reference frame. Much
appreciated!
John


On Wed, Jun 30, 2010 at 12:22 AM, Loren Merritt <lorenm at u.washington.edu> wrote:
> 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
>
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