Scene-cut detection: avoid very short KF intervals
In some videos with camera panning, scene cut algo incorrectly
identifies a scene cut after just a couple of frames.
We force a bigger keyframe interval to avoid this issue.
Large BDRate improvement on selected videos:
hdres/shields_720p50.y4m: -10.717
hdres/stockholm_ter_720p60.y4m: -10.312
hdres/parkrun_720p50.y4m: -3.501
hdres/mobcal_720p50.y4m: -2.405
(other hdres vids neutral)
hdres overall: -0.709
lowres, midres, ugc360p and objective1-fast all neutral.
STATS_CHANGED
Change-Id: I601a306d2657f74ca8ebf5105f4cbf02121bf0ce
diff --git a/av1/encoder/pass2_strategy.c b/av1/encoder/pass2_strategy.c
index 3e5f17f..b135938 100644
--- a/av1/encoder/pass2_strategy.c
+++ b/av1/encoder/pass2_strategy.c
@@ -1405,7 +1405,8 @@
// Does the frame satisfy the primary criteria of a key frame?
// See above for an explanation of the test criteria.
// If so, then examine how well it predicts subsequent frames.
- if ((this_frame->pcnt_second_ref < second_ref_usage_thresh) &&
+ if (frame_count_so_far >= 3 &&
+ (this_frame->pcnt_second_ref < second_ref_usage_thresh) &&
(next_frame->pcnt_second_ref < second_ref_usage_thresh) &&
((this_frame->pcnt_inter < VERY_LOW_INTER_THRESH) ||
((pcnt_intra > MIN_INTRA_LEVEL) &&
