shithub: libvpx

Info  •  Files  •  Log  •  Branches

vp9: Rate control fix for CBR mode.

For CBR mode: modify the qp clamping to allow q to respond
faster to overshoot. Can reduce some suprious overshoot events
observed in screen content coding.

Change-Id: I0b3f54b0d1b4086182f834e557a4121950b176d4

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

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

@@ -620,8 +620,14 @@

        !(cpi->refresh_alt_ref_frame || cpi->refresh_golden_frame)) &&

       (cpi->rc.rc_1_frame * cpi->rc.rc_2_frame == -1) &&

       cpi->rc.q_1_frame != cpi->rc.q_2_frame) {

-    q = clamp(q, VPXMIN(cpi->rc.q_1_frame, cpi->rc.q_2_frame),

-              VPXMAX(cpi->rc.q_1_frame, cpi->rc.q_2_frame));

+    int qclamp = clamp(q, VPXMIN(cpi->rc.q_1_frame, cpi->rc.q_2_frame),

+                       VPXMAX(cpi->rc.q_1_frame, cpi->rc.q_2_frame));

+    // If the previous had overshoot and the current q needs to increase above

+    // the clamped value, reduce the clamp for faster reaction to overshoot.

+    if (cpi->rc.rc_1_frame == -1 && q > qclamp)

+      q = (q + qclamp) >> 1;

+    else

+      q = qclamp;

   }

   return q;

 }