shithub: libvpx

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Tuning of factor used to calculate Q range in two pass.

A more detailed explanation of the experimentation
leading to this change can be found in:-

https://docs.google.com/a/google.com/document/d/13lsYhxgPyxUHvEess6wg9nikaonIZKY9Ak_Lpafv5Mo/edit?usp=sharing

This change gives gains across all our standard test sets for
overall psnr, ssim, fast ssim and psnr-HVS.

Values expressed as % reduction in bitrate.

Low res set     -0.257, -0.192, -0.173, -0.101
Mid res set     -0.233, -0.336, -0.367, -0.139
High res set    -0.999, -1.039, -1.111, -0.567
NetFlix 2K set -0.734, -0.174, -0.389, -0.820
Netflix 4K set  -0.814, -0.485, -0.796, -0.839

Change-Id: Ie981fb3c895c9dfcfc8682640d201a86375db5c8

--- a/vp9/encoder/vp9_firstpass.c

+++ b/vp9/encoder/vp9_firstpass.c

@@ -42,8 +42,6 @@

 #define OUTPUT_FPF 0

 #define ARF_STATS_OUTPUT 0

-#define FACTOR_PT_LOW 0.70

-#define FACTOR_PT_HIGH 0.90

 #define FIRST_PASS_Q 10.0

 #define GF_MAX_BOOST 96.0

 #define INTRA_MODE_PENALTY 1024

@@ -50,7 +48,6 @@

 #define MIN_ARF_GF_BOOST 240

 #define MIN_DECAY_FACTOR 0.01

 #define NEW_MV_MODE_PENALTY 32

-#define SVC_FACTOR_PT_LOW 0.45

 #define DARK_THRESH 64

 #define DEFAULT_GRP_WEIGHT 1.0

 #define RC_FACTOR_MIN 0.75

@@ -1522,15 +1519,23 @@

   if (cpi->use_svc) vp9_inc_frame_in_layer(cpi);

 }

+static const double q_pow_term[(QINDEX_RANGE >> 5) + 1] = {

+  0.65, 0.70, 0.75, 0.85, 0.90, 0.90, 0.90, 1.00, 1.25

+};

+

 static double calc_correction_factor(double err_per_mb, double err_divisor,

-                                     double pt_low, double pt_high, int q,

-                                     vpx_bit_depth_t bit_depth) {

-  const double error_term = err_per_mb / err_divisor;

+                                     int q) {

+  const double error_term = err_per_mb / DOUBLE_DIVIDE_CHECK(err_divisor);

+  const int index = q >> 5;

+  double power_term;

-  // Adjustment based on actual quantizer to power term.

-  const double power_term =

-      VPXMIN(vp9_convert_qindex_to_q(q, bit_depth) * 0.01 + pt_low, pt_high);

+  assert((index >= 0) && (index < (QINDEX_RANGE >> 5)));

+  // Adjustment based on quantizer to the power term.

+  power_term =

+      q_pow_term[index] +

+      (((q_pow_term[index + 1] - q_pow_term[index]) * (q % 32)) / 32.0);

+

   // Calculate correction factor.

   if (power_term < 1.0) assert(error_term >= 0.0);

@@ -1567,11 +1572,7 @@

     const int target_norm_bits_per_mb =

         (int)(((uint64_t)target_rate << BPER_MB_NORMBITS) / active_mbs);

     int q;

-    int is_svc_upper_layer = 0;

-    if (is_two_pass_svc(cpi) && cpi->svc.spatial_layer_id > 0)

-      is_svc_upper_layer = 1;

-

     // based on recent history adjust expectations of bits per macroblock.

     last_group_rate_err =

         (double)twopass->rolling_arf_group_actual_bits /

@@ -1583,10 +1584,8 @@

     // Try and pick a max Q that will be high enough to encode the

     // content at the given rate.

     for (q = rc->best_quality; q < rc->worst_quality; ++q) {

-      const double factor = calc_correction_factor(

-          av_err_per_mb, ERR_DIVISOR,

-          is_svc_upper_layer ? SVC_FACTOR_PT_LOW : FACTOR_PT_LOW,

-          FACTOR_PT_HIGH, q, cpi->common.bit_depth);

+      const double factor =

+          calc_correction_factor(av_err_per_mb, ERR_DIVISOR, q);

       const int bits_per_mb = vp9_rc_bits_per_mb(

           INTER_FRAME, q,

           factor * speed_term * cpi->twopass.bpm_factor * noise_factor,