Adapt GOP size threshold to the allowed layer depth

Increase the total prediction error budget linearly with the
allowed ARF layer depth. This in general improves the compression
performance, but does hit corner cases on a few clips at very
low bit-rate range (corresponding to 26 - 28 dB range). To mitigate
such problem, we temporarily work around this problem by limiting
the first GOP size to be ~8 so as to not drain up the bit resource.

The overall compression performance improvements over the current
multi-layer ARF system in speed 0 are:

           overall PSNR      avg PSNR        SSIM
lowres     -0.47%            -0.13%         -1.51%
midres     -1.30%            -1.16%         -2.80%
hdres      -0.91%            -0.84%         -2.15%

Change-Id: Ia4880ab63e98e15a9db99aea6eabfd3d1da9270d

diff --git a/vp9/encoder/vp9_firstpass.c b/vp9/encoder/vp9_firstpass.c
index 38e98cd1eb354fb791cdd3739db183e5ea3f6018..2391cb7a6d3a45f21f8dbf2eb6f47d3872fd3f2c 100644 (file)
--- a/vp9/encoder/vp9_firstpass.c
+++ b/vp9/encoder/vp9_firstpass.c
@@ -2485,6 +2485,8 @@ static void define_gf_group(VP9_COMP *cpi, FIRSTPASS_STATS *this_frame) {
   const int is_key_frame = frame_is_intra_only(cm);
   const int arf_active_or_kf = is_key_frame || rc->source_alt_ref_active;
 
+  int gop_intra_factor = 0;
+
   // Reset the GF group data structures unless this is a key
   // frame in which case it will already have been done.
   if (is_key_frame == 0) {
@@ -2537,6 +2539,12 @@ static void define_gf_group(VP9_COMP *cpi, FIRSTPASS_STATS *this_frame) {
     // interval to spread the cost of the GF.
     active_max_gf_interval = 12 + arf_active_or_kf + VPXMIN(4, (int_lbq / 6));
 
+    // TODO(jingning, paulwilkins): Temporary solution to work around
+    // multi-layer ARF rate control issues at extremely low bit-rate cases.
+    // We would deprecate this soon.
+    if (cpi->multi_layer_arf && is_key_frame)
+      active_max_gf_interval = 7 + arf_active_or_kf + VPXMIN(4, (int_lbq / 6));
+
     // We have: active_min_gf_interval <=
     // rc->max_gf_interval + arf_active_or_kf.
     if (active_max_gf_interval < active_min_gf_interval) {
@@ -2552,6 +2560,11 @@ static void define_gf_group(VP9_COMP *cpi, FIRSTPASS_STATS *this_frame) {
       active_max_gf_interval = rc->frames_to_key / 2;
   }
 
+  // Adapt the intra_error factor to active_max_gf_interval limit.
+  for (i = active_max_gf_interval; i > 0; i >>= 1) ++gop_intra_factor;
+
+  gop_intra_factor = VPXMIN(MAX_ARF_LAYERS, gop_intra_factor);
+
   i = 0;
   while (i < rc->static_scene_max_gf_interval && i < rc->frames_to_key) {
     ++i;
@@ -2628,7 +2641,7 @@ static void define_gf_group(VP9_COMP *cpi, FIRSTPASS_STATS *this_frame) {
             (!flash_detected) &&
             ((mv_ratio_accumulator > mv_ratio_accumulator_thresh) ||
              (abs_mv_in_out_accumulator > abs_mv_in_out_thresh) ||
-             (sr_accumulator > next_frame.intra_error)))) {
+             (sr_accumulator > gop_intra_factor * next_frame.intra_error)))) {
       break;
     }