tree 6cf62fe6a3e30ef7e1837255a76ef3cf7772c9bf
parent b9f57bc86083d7c69d073f9d8dc22dc89693394c
author bohanli <bohanli@google.com> 1582660691 -0800
committer Bohan Li <bohanli@google.com> 1583192074 +0000

Adjust gop shrinking for 32 length.

This patch adds various adjustments to better work with the 32
length gop:
1: change the logic when using tpl to determine longer or shorter
   gop. If decided to use longer, or lag-in-frames is not
   sufficient, we can still benefit from lookahead and lookback.
2: fix a problem of coded error lookup when we do not start with
   a key frame in the current gf group. This way the padding is
   also available to gf groups that are decided individually.
3: change the minimum shrinking length to 6, in order to benefit
   individually determined gf groups.
4: now if user decides to restrain the max length to 16, we should
   have a better performance.

On lag-in-frames=35, we have some minor gains on average:

test results (BD-rate, %)  on speed 1:
     	     avg_PSNR	overall_PSNR	ssim	VMAF
lowres	     -0.007	-0.017		-0.017	-0.124
midres	      0.016	 0.074		 0.194	-0.025
hdres	     -0.059	-0.068		-0.096	-0.065
ugc360p	     -0.134	-0.055		-0.064	-0.132

on speed 4:
     	     avg_PSNR	overall_PSNR	ssim	VMAF
lowres	     -0.078	-0.081		-0.056	-0.092
midres	     -0.021	 0.041		 0.131	-0.065
hdres	     -0.004	-0.014		-0.079	-0.060
ugc360p	     -0.206	-0.209		-0.247	-0.229

most gains in ugc360p, where it is not very stable and padding
could help most.
Changes on other test sets are small.

STATS_CHANGED

Change-Id: Ia43ff93a1a1943e53856f3109e1b0e476b9f3016