Bug when last group before forced key frame is short.

Just before a forced key frame we often get a foreshortened
arf/gf group. In such a case, we do not want to update
rc->last_boosted_qindex, which is used to define the Q range
for the forced key frame itself.

This gives a small average metrics gain for the YT and YT-HD sets
(eg. YT SSIM +0.141%).

Change-Id: Ie06698bc4f249e87183b8f8fb27ff8f3fde216d9

3 files changed, 12 insertions, 2 deletions

diff --git a/vp9/encoder/vp9_firstpass.c b/vp9/encoder/vp9_firstpass.c
index 74f5efbec..3b0f2f012 100644
--- a/vp9/encoder/vp9_firstpass.c
+++ b/vp9/encoder/vp9_firstpass.c
@@ -1843,6 +1843,9 @@ static void define_gf_group(VP9_COMP *cpi, FIRSTPASS_STATS *this_frame) {
 
   twopass->gf_zeromotion_pct = (int)(zero_motion_accumulator * 1000.0);
 
+  // Was the group length constrained by the requirement for a new KF?
+  rc->constrained_gf_group = (i >= rc->frames_to_key) ? 1 : 0;
+
   // Set the interval until the next gf.
   if (cpi->common.frame_type == KEY_FRAME || rc->source_alt_ref_active)
     rc->baseline_gf_interval = i - 1;
diff --git a/vp9/encoder/vp9_ratectrl.c b/vp9/encoder/vp9_ratectrl.c
index 3cc9d9a7b..21f4cce03 100644
--- a/vp9/encoder/vp9_ratectrl.c
+++ b/vp9/encoder/vp9_ratectrl.c
@@ -1254,7 +1254,9 @@ void vp9_rc_postencode_update(VP9_COMP *cpi, uint64_t bytes_used) {
   // better than that already stored.
   // This is used to help set quality in forced key frames to reduce popping
   if ((qindex < rc->last_boosted_qindex) ||
-      (((cm->frame_type == KEY_FRAME) || cpi->refresh_alt_ref_frame ||
+      (cm->frame_type == KEY_FRAME) ||
+      (!rc->constrained_gf_group &&
+       (cpi->refresh_alt_ref_frame ||
         (cpi->refresh_golden_frame && !rc->is_src_frame_alt_ref)))) {
     rc->last_boosted_qindex = qindex;
   }
@@ -1358,8 +1360,12 @@ void vp9_rc_get_one_pass_vbr_params(VP9_COMP *cpi) {
     rc->baseline_gf_interval = DEFAULT_GF_INTERVAL;
     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)
+    if (rc->frames_till_gf_update_due > rc->frames_to_key) {
       rc->frames_till_gf_update_due = rc->frames_to_key;
+      rc->constrained_gf_group = 1;
+    } else {
+      rc->constrained_gf_group = 0;
+    }
     cpi->refresh_golden_frame = 1;
     rc->source_alt_ref_pending = USE_ALTREF_FOR_ONE_PASS;
     rc->gfu_boost = DEFAULT_GF_BOOST;
diff --git a/vp9/encoder/vp9_ratectrl.h b/vp9/encoder/vp9_ratectrl.h
index cf709274d..a53f4e0a2 100644
--- a/vp9/encoder/vp9_ratectrl.h
+++ b/vp9/encoder/vp9_ratectrl.h
@@ -55,6 +55,7 @@ typedef struct {
   int max_gf_interval;
   int static_scene_max_gf_interval;
   int baseline_gf_interval;
+  int constrained_gf_group;
   int frames_to_key;
   int frames_since_key;
   int this_key_frame_forced;