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Use undamped adjustment for rate correction factors

Undamped adjustment is used for the first frame
of each frame type while updating the rate
correction factors.

Change-Id: I42f80daa123c4cd4e45c18c6960cc7a67e7df7e6

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

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

@@ -417,6 +417,7 @@

   for (i = 0; i < RATE_FACTOR_LEVELS; ++i) {

     rc->rate_correction_factors[i] = 1.0;

+    rc->damped_adjustment[i] = 0;

   }

   rc->min_gf_interval = oxcf->min_gf_interval;

@@ -720,6 +721,8 @@

   int correction_factor = 100;

   double rate_correction_factor = get_rate_correction_factor(cpi);

   double adjustment_limit;

+  RATE_FACTOR_LEVEL rf_lvl =

+      cpi->twopass.gf_group.rf_level[cpi->twopass.gf_group.index];

   int projected_size_based_on_q = 0;

@@ -746,10 +749,16 @@

     correction_factor = (int)((100 * (int64_t)cpi->rc.projected_frame_size) /

                               projected_size_based_on_q);

-  // More heavily damped adjustment used if we have been oscillating either side

-  // of target.

-  adjustment_limit =

-      0.25 + 0.5 * VPXMIN(1, fabs(log10(0.01 * correction_factor)));

+  // Do not use damped adjustment for the first frame of each frame type

+  if (!cpi->rc.damped_adjustment[rf_lvl]) {

+    adjustment_limit = 1.0;

+    cpi->rc.damped_adjustment[rf_lvl] = 1;

+  } else {

+    // More heavily damped adjustment used if we have been oscillating either

+    // side of target.

+    adjustment_limit =

+        0.25 + 0.5 * VPXMIN(1, fabs(log10(0.01 * correction_factor)));

+  }

   cpi->rc.q_2_frame = cpi->rc.q_1_frame;

   cpi->rc.q_1_frame = cm->base_qindex;

--- a/vp9/encoder/vp9_ratectrl.h

+++ b/vp9/encoder/vp9_ratectrl.h

@@ -195,6 +195,8 @@

   int use_post_encode_drop;

   // External flag to enable post encode frame dropping, controlled by user.

   int ext_use_post_encode_drop;

+

+  int damped_adjustment[RATE_FACTOR_LEVELS];

 } RATE_CONTROL;

 struct VP9_COMP;