shithub: libvpx

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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

--- a/vp9/encoder/vp9_firstpass.c

+++ b/vp9/encoder/vp9_firstpass.c

@@ -1843,6 +1843,9 @@

   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;

--- a/vp9/encoder/vp9_ratectrl.c

+++ b/vp9/encoder/vp9_ratectrl.c

@@ -1254,7 +1254,9 @@

   // 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 @@

     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;

--- a/vp9/encoder/vp9_ratectrl.h

+++ b/vp9/encoder/vp9_ratectrl.h

@@ -55,6 +55,7 @@

   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;