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L2E: let vp9 encoder respect external max frame size constraint

Change-Id: Ib926e694d4bc4675af1435a32f6316a587756380

--- a/vp9/encoder/vp9_encoder.c

+++ b/vp9/encoder/vp9_encoder.c

@@ -4398,6 +4398,7 @@

   int frame_over_shoot_limit;

   int frame_under_shoot_limit;

   int q = 0, q_low = 0, q_high = 0;

+  int last_q_attempt = 0;

   int enable_acl;

 #ifdef AGGRESSIVE_VBR

   int qrange_adj = 1;

@@ -4413,6 +4414,7 @@

   // passed in by the external rate control model.

   // case: -1, we take VP9's decision for the max frame size.

   int ext_rc_max_frame_size = 0;

+  const int orig_rc_max_frame_bandwidth = rc->max_frame_bandwidth;

 #if CONFIG_RATE_CTRL

   const FRAME_UPDATE_TYPE update_type =

@@ -4580,6 +4582,7 @@

     }

     if (cpi->ext_ratectrl.ready) {

+      last_q_attempt = q;

       // In general, for the external rate control, we take the qindex provided

       // as input and encode the frame with this qindex faithfully. However,

       // in some extreme scenarios, the provided qindex leads to a massive

@@ -4597,6 +4600,10 @@

           break;

         }

       }

+      rc->max_frame_bandwidth = ext_rc_max_frame_size;

+      // If the current frame size exceeds the ext_rc_max_frame_size,

+      // we adjust the worst qindex to meet the frame size constraint.

+      q_high = 255;

       ext_rc_recode = 1;

     }

 #if CONFIG_RATE_CTRL

@@ -4796,6 +4803,23 @@

         rc->projected_frame_size < rc->max_frame_bandwidth)

       loop = 0;

+    // Special handling of external max frame size constraint

+    if (ext_rc_recode) {

+      // If the largest q is not able to meet the max frame size limit,

+      // do nothing.

+      if (rc->projected_frame_size > ext_rc_max_frame_size &&

+          last_q_attempt == 255) {

+        break;

+      }

+      // If VP9's q selection leads to a smaller q, we force it to use

+      // a larger q to better approximate the external max frame size

+      // constraint.

+      if (rc->projected_frame_size > ext_rc_max_frame_size &&

+          q <= last_q_attempt) {

+        q = VPXMIN(255, last_q_attempt + 1);

+      }

+    }

+

     if (loop) {

       ++loop_count;

       ++loop_at_this_size;

@@ -4808,6 +4832,8 @@

     if (cpi->sf.recode_loop >= ALLOW_RECODE_KFARFGF)

       if (loop) restore_coding_context(cpi);

   } while (loop);

+

+  rc->max_frame_bandwidth = orig_rc_max_frame_bandwidth;

 #ifdef AGGRESSIVE_VBR

   if (two_pass_first_group_inter(cpi)) {