shithub: libvpx

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Don't use compound prediction for golden frames based on alt-ref frames.

These frames can force reference frame (arf), mode (zeromv) and skip,
which means that if we use compound prediction (i.e. arf+last), we
might use a blend of a perfect (arf) and an imperfect (last) predictor,
leading to semi-garbage display and thus a huge drop in SSIM/PSNR (up
to 10dB for some frames I analyzed).

Gives a +0.2% gain on YT.

Change-Id: If1f2b7899ad165684af3808fd379295e82558cbb

--- a/vp8/encoder/encodeframe.c

+++ b/vp8/encoder/encodeframe.c

@@ -1288,11 +1288,13 @@

         else

             frame_type = 2;

-        if (cpi->rd_prediction_type_threshes[frame_type][1] >

-                cpi->rd_prediction_type_threshes[frame_type][0] &&

-            cpi->rd_prediction_type_threshes[frame_type][1] >

-                cpi->rd_prediction_type_threshes[frame_type][2] &&

-            check_dual_ref_flags(cpi))

+        if (frame_type == 3)

+            pred_type = SINGLE_PREDICTION_ONLY;

+        else if (cpi->rd_prediction_type_threshes[frame_type][1] >

+                    cpi->rd_prediction_type_threshes[frame_type][0] &&

+                 cpi->rd_prediction_type_threshes[frame_type][1] >

+                    cpi->rd_prediction_type_threshes[frame_type][2] &&

+                 check_dual_ref_flags(cpi))

             pred_type = COMP_PREDICTION_ONLY;

         else if (cpi->rd_prediction_type_threshes[frame_type][0] >

                     cpi->rd_prediction_type_threshes[frame_type][1] &&

-- 

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