Fix ARF rate allocation for cq mode

In the limited test set, it improves the cq mode compression
performance by 1.9% in PSNR and 6% in SSIM as compared to use
same quantization parameter for all ARFs.

Change-Id: I35c4d7097b5838ab0b92d7f9937520721e3bb84b

diff --git a/vp9/encoder/vp9_ratectrl.c b/vp9/encoder/vp9_ratectrl.c
index 779529b..d081f1a 100644 (file)
--- a/vp9/encoder/vp9_ratectrl.c
+++ b/vp9/encoder/vp9_ratectrl.c
@@ -1364,6 +1364,16 @@ static int rc_pick_q_and_bounds_two_pass(const VP9_COMP *cpi, int *bottom_index,
       // Constrained quality use slightly lower active best.
       active_best_quality = active_best_quality * 15 / 16;
 
+      // Modify best quality for second level arfs. For mode VPX_Q this
+      // becomes the baseline frame q.
+      if (gf_group->rf_level[gf_group_index] == GF_ARF_LOW) {
+        const int layer_depth = gf_group->layer_depth[gf_group_index];
+        // linearly fit the frame q depending on the layer depth index from
+        // the base layer ARF.
+        active_best_quality =
+            ((layer_depth - 1) * q + active_best_quality + layer_depth / 2) /
+            layer_depth;
+      }
     } else if (oxcf->rc_mode == VPX_Q) {
       if (!cpi->refresh_alt_ref_frame) {
         active_best_quality = cq_level;