vp9: 1 pass vbr: More even spacing for gf near key frame.

More even spacing near key frame and avoid gf on scene cut
if its close to key frame.

Small increase in metrics for ytlive set (which uses key-period=150).
(~0.2% gain)

Change only affects 1 pass vbr mode.

Change-Id: If1e5a59baf1e0befbaf998522fbc47d94ac5b5df

vp9/encoder/vp9_ratectrl.c

diff --git a/vp9/encoder/vp9_ratectrl.c b/vp9/encoder/vp9_ratectrl.c
index 300080b..07a8344 100644
--- a/vp9/encoder/vp9_ratectrl.c
+++ b/vp9/encoder/vp9_ratectrl.c
@@ -1506,6 +1506,11 @@
       rc->baseline_gf_interval =
           (rc->min_gf_interval + rc->max_gf_interval) / 2;
     }
+    // Reset the gf interval to make more equal spacing for up-coming key frame.
+    if ((rc->frames_to_key <= 7 * rc->baseline_gf_interval >> 2) &&
+        (rc->frames_to_key > rc->baseline_gf_interval)) {
+      rc->baseline_gf_interval = rc->frames_to_key >> 1;
+    }
     rc->frames_till_gf_update_due = rc->baseline_gf_interval;
     // NOTE: frames_till_gf_update_due must be <= frames_to_key.
     if (rc->frames_till_gf_update_due > rc->frames_to_key) {
@@ -2092,6 +2097,7 @@
     // For VBR, under scene change/high content change, force golden refresh.
     if (cpi->oxcf.rc_mode == VPX_VBR &&
         rc->high_source_sad &&
+        rc->frames_to_key > 3 &&
         rc->count_last_scene_change > 4 &&
         cpi->ext_refresh_frame_flags_pending == 0) {
       int target;