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