shithub: libvpx

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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

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

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

@@ -1364,6 +1364,16 @@

       // 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;