Does rc-lookahead...

[pwnsweet]

A quick question about rc-lookahead. The MeWiki x264 settings site states: "increasing the frame count generates better results but is also slower" but it mentions nothing about file size. So does increasing the value for rc-lookahead:

a) Increase image quality and increase file size
b) Increase image quality and decrease file size
c) Maintain image quality and decrease file size

[Dark Shikari]

d) provide basically zero benefit besides making you feel better.

[pwnsweet]

I've gone ahead and encoded the same video at the same CQ=22 setting, once with rc-lookahead at default (40) and again at 250. The 250 file took 6.8% longer to encode, is 0.4% larger in size and required roughly 2.5x the amount of system memory (RAM). There is no discernible difference in visual quality. I think it's safe to say option d) above is the correct one.

[upyzl]

I've gone ahead and encoded the same video at the same CQ=22 setting, once with rc-lookahead at default (40) and again at 250. The 250 file took 6.8% longer to encode, is 0.4% larger in size and required roughly 2.5x the amount of system memory (RAM). There is no discernible difference in visual quality. I think it's safe to say option d) above is the correct one.

Maybe you'd better try using same 2pass bitrate(and the bitrate is low enough, such as ~Avg.QP 27 for P-frames with other default params) to compare different rc-lookahead

Also, lower qcomp (http://mewiki.project357.com/wiki/X264_Settings#qcomp)(0.6->0.5) when use very high rc-lookahead may be more helpful

Anyway, I like using 60