shithub: libvpx

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vp9: Rate control adjustments for screen content.

For screen content mode: changes to reduce occurence of
significant QP decrease (from one frame to next),
which can cause large frames (overshoot/delay).
-cap the buffer increase to optimal level for frame drop
mode where full superframe can drop
-reduce the max_adjustment_down due to buffer overflow
-reduce qp threshold to trigger re-encode on large frame

Change-Id: I3e30e4814192b5f728abff3f7359eb64f561b8f0

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

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

@@ -273,6 +273,14 @@

   const VP9_COMMON *const cm = &cpi->common;

   RATE_CONTROL *const rc = &cpi->rc;

+  // On dropped frame, don't update buffer if its currently stable

+  // (above optimal level). This can cause issues when full superframe

+  // can drop (!= LAYER_DROP), since QP is adjusted downwards with buffer

+  // overflow, which can cause more frame drops.

+  if (cpi->svc.framedrop_mode != LAYER_DROP && encoded_frame_size == 0 &&

+      rc->buffer_level > rc->optimal_buffer_level)

+    return;

+

   // Non-viewable frames are a special case and are treated as pure overhead.

   if (!cm->show_frame) {

     rc->bits_off_target -= encoded_frame_size;

@@ -770,8 +778,10 @@

   active_worst_quality = VPXMIN(rc->worst_quality, ambient_qp * 5 >> 2);

   if (rc->buffer_level > rc->optimal_buffer_level) {

     // Adjust down.

-    // Maximum limit for down adjustment, ~30%.

+    // Maximum limit for down adjustment ~30%; make it lower for screen content.

     int max_adjustment_down = active_worst_quality / 3;

+    if (cpi->oxcf.content == VP9E_CONTENT_SCREEN)

+      max_adjustment_down = active_worst_quality >> 3;

     if (max_adjustment_down) {

       buff_lvl_step = ((rc->maximum_buffer_size - rc->optimal_buffer_level) /

                        max_adjustment_down);

@@ -2512,7 +2522,7 @@

 int vp9_encodedframe_overshoot(VP9_COMP *cpi, int frame_size, int *q) {

   VP9_COMMON *const cm = &cpi->common;

   RATE_CONTROL *const rc = &cpi->rc;

-  int thresh_qp = 3 * (rc->worst_quality >> 2);

+  int thresh_qp = 7 * (rc->worst_quality >> 3);

   int thresh_rate = rc->avg_frame_bandwidth << 3;

   // Lower rate threshold for video.

   if (cpi->oxcf.content != VP9E_CONTENT_SCREEN)