Implement basic rate control.

src/Makefile

@@ -86,6 +86,7 @@ OBJS = \
   cu.o \
   encoder.o \
   encoderstate.o \
+  rate_control.o \
   filter.o \
   inter.o \
   intra.o \

src/encoderstate.c

@@ -43,6 +43,7 @@
 #include "search.h"
 #include "sao.h"
 #include "rdo.h"
+#include "rate_control.h"
 
 #ifndef LMBD
 # define LMBD 1.0
@@ -812,6 +813,8 @@ static void encoder_state_new_frame(encoder_state_t * const state) {
         state->global->QP_factor = state->encoder_control->cfg->gop[state->global->gop_offset].qp_factor;
       }
         
+    } else {
+      state->global->QP = select_picture_QP(state);
     }
 
   } else {

src/rate_control.c

@@ -0,0 +1,66 @@
+/*****************************************************************************
+ * This file is part of Kvazaar HEVC encoder.
+ *
+ * Copyright (C) 2013-2015 Tampere University of Technology and others (see
+ * COPYING file).
+ *
+ * Kvazaar is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation; either version 2.1 of the License, or (at your
+ * option) any later version.
+ *
+ * Kvazaar is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with Kvazaar.  If not, see <http://www.gnu.org/licenses/>.
+ ****************************************************************************/
+
+#include "rate_control.h"
+
+#include <math.h>
+
+static const int SMOOTHING_WINDOW = 40;
+
+/**
+ * \brief Select a QP for encoding the next picture
+ * \param state the main encoder state
+ * \return the QP for the next picture, in range [0, 51]
+ */
+int8_t select_picture_QP(const encoder_state_t * const state)
+{
+  const encoder_control_t * const encoder = state->encoder_control;
+
+  if (encoder->cfg->target_bitrate <= 0) {
+    // Rate control disabled.
+    return encoder->cfg->qp;
+  }
+
+  // At this point, total_bits_coded of the current state contains the
+  // number of bits written encoder->owf frames before the current frame.
+  const int bits_coded = state->global->total_bits_coded;
+  const int pictures_coded = MAX(0, state->global->frame - encoder->owf);
+
+  const double avg_bits_per_picture =
+    encoder->cfg->target_bitrate / encoder->cfg->framerate;
+
+  // TODO: use picture weights
+  const double target_bits_current_picture =
+    (avg_bits_per_picture * (pictures_coded + SMOOTHING_WINDOW) - bits_coded)
+    / SMOOTHING_WINDOW;
+
+  // TODO: take the picture headers into account
+  const int pixels_per_picture = encoder->in.width * encoder->in.height;
+  const double target_bits_per_pixel = target_bits_current_picture / pixels_per_picture;
+
+  // The following magical constants, -5.7420835 and 18.598408755005686 are
+  // based on the values given in
+  //
+  //   K. McCann et al., "High Effiency Video Coding (HEVC) Test Model 16
+  //   (HM 16) Improved Encoder Description", JCTVC-S1002, October 2014,
+  //   (p. 52 - 54)
+  const int QP = (int)(-5.7420835 * log(MAX(target_bits_per_pixel, 0.001)) + 18.598408755005686);
+  return CLIP(0, 51, QP);
+}

src/rate_control.h

@@ -0,0 +1,32 @@
+#ifndef RATE_CONTROL_H_
+#define RATE_CONTROL_H_
+/*****************************************************************************
+ * This file is part of Kvazaar HEVC encoder.
+ *
+ * Copyright (C) 2013-2015 Tampere University of Technology and others (see
+ * COPYING file).
+ *
+ * Kvazaar is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation; either version 2.1 of the License, or (at your
+ * option) any later version.
+ *
+ * Kvazaar is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with Kvazaar.  If not, see <http://www.gnu.org/licenses/>.
+ ****************************************************************************/
+
+/*
+ * \file
+ * \brief Functions related with rate control
+ */
+
+#include "encoderstate.h"
+
+int8_t select_picture_QP(const encoder_state_t * const state);
+
+#endif // RATE_CONTROL_H_