1. ffmpeg
  2. Commit e500315b1dd7654ec550b5fc013232b3567358e0
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gain code, gain pitch and pitch delay decoding for ACELP based codecs

Originally committed as revision 14037 to svn://svn.ffmpeg.org/ffmpeg/trunk

Vladimir Voroshilov authored on 2008/07/01 03:03:38
Showing 2 changed files
libavcodec/acelp_pitch_delay.c
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+/*
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+ * gain code, gain pitch and pitch delay decoding
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+ *
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+ * Copyright (c) 2008 Vladimir Voroshilov
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+ *
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+ * This file is part of FFmpeg.
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+ *
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+ * FFmpeg is free software; you can redistribute it and/or
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+ * modify it under the terms of the GNU Lesser General Public
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+ * License as published by the Free Software Foundation; either
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+ * version 2.1 of the License, or (at your option) any later version.
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+ *
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+ * FFmpeg is distributed in the hope that it will be useful,
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+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
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+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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+ * Lesser General Public License for more details.
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+ *
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+ * You should have received a copy of the GNU Lesser General Public
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+ * License along with FFmpeg; if not, write to the Free Software
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+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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+ */
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+
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+#include "avcodec.h"
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+#include "acelp_pitch_delay.h"
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+#include "acelp_math.h"
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+
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+int ff_acelp_decode_8bit_to_1st_delay3(int ac_index)
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+{
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+    ac_index += 58;
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+    if(ac_index > 254)
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+        ac_index = 3 * ac_index - 510;
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+    return ac_index;
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+}
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+
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+int ff_acelp_decode_4bit_to_2nd_delay3(
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+        int ac_index,
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+        int pitch_delay_min)
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+{
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+    if(ac_index < 4)
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+        return 3 * (ac_index + pitch_delay_min);
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+    else if(ac_index < 12)
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+        return 3 * pitch_delay_min + ac_index + 6;
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+    else
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+        return 3 * (ac_index + pitch_delay_min) - 18;
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+}
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+
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+int ff_acelp_decode_5_6_bit_to_2nd_delay3(
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+        int ac_index,
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+        int pitch_delay_min)
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+{
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+        return 3 * pitch_delay_min + ac_index - 2;
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+}
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+
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+int ff_acelp_decode_9bit_to_1st_delay6(int ac_index)
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+{
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+    if(ac_index < 463)
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+        return ac_index + 105;
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+    else
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+        return 6 * (ac_index - 368);
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+}
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+int ff_acelp_decode_6bit_to_2nd_delay6(
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+        int ac_index,
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+        int pitch_delay_min)
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+{
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+    return 6 * pitch_delay_min + ac_index - 3;
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+}
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+
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+void ff_acelp_update_past_gain(
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+    int16_t* quant_energy,
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+    int gain_corr_factor,
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+    int log2_ma_pred_order,
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+    int erasure)
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+{
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+    int i;
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+    int avg_gain=quant_energy[(1 << log2_ma_pred_order) - 1]; // (5.10)
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+
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+    for(i=(1 << log2_ma_pred_order) - 1; i>0; i--)
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+    {
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+        avg_gain       += quant_energy[i-1];
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+        quant_energy[i] = quant_energy[i-1];
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+    }
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+
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+    if(erasure)
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+        quant_energy[0] = FFMAX(avg_gain >> log2_ma_pred_order, -10240) - 4096; // -10 and -4 in (5.10)
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+    else
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+        quant_energy[0] = (6165 * ((ff_log2(gain_corr_factor) >> 2) - (13 << 13))) >> 13;
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+}
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+
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+int16_t ff_acelp_decode_gain_code(
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+    int gain_corr_factor,
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+    const int16_t* fc_v,
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+    int mr_energy,
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+    const int16_t* quant_energy,
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+    const int16_t* ma_prediction_coeff,
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+    int subframe_size,
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+    int ma_pred_order)
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+{
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+    int i;
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+
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+    mr_energy <<= 10;
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+
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+    for(i=0; i<ma_pred_order; i++)
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+        mr_energy += quant_energy[i] * ma_prediction_coeff[i];
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+
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+#ifdef G729_BITEXACT
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+    mr_energy += (((-6165LL * ff_log2(sum_of_squares(fc_v, subframe_size, 0, 0))) >> 3) & ~0x3ff);
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+
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+    mr_energy = (5439 * (mr_energy >> 15)) >> 8;           // (0.15) = (0.15) * (7.23)
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+
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+    return bidir_sal(
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+               ((ff_exp2(mr_energy & 0x7fff) + 16) >> 5) * (gain_corr_factor >> 1),
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+               (mr_energy >> 15) - 25
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+           );
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+#else
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+    mr_energy = gain_corr_factor * exp(M_LN10 / (20 << 23) * mr_energy) /
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+                sqrt(sum_of_squares(fc_v, subframe_size, 0, 0));
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+    return mr_energy >> 12;
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+#endif
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+}
libavcodec/acelp_pitch_delay.h
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+/*
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+ * gain code, gain pitch and pitch delay decoding
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+ *
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+ * Copyright (c) 2008 Vladimir Voroshilov
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+ *
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+ * This file is part of FFmpeg.
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+ *
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+ * FFmpeg is free software; you can redistribute it and/or
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+ * modify it under the terms of the GNU Lesser General Public
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+ * License as published by the Free Software Foundation; either
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+ * version 2.1 of the License, or (at your option) any later version.
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+ *
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+ * FFmpeg is distributed in the hope that it will be useful,
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+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
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+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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+ * Lesser General Public License for more details.
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+ *
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+ * You should have received a copy of the GNU Lesser General Public
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+ * License along with FFmpeg; if not, write to the Free Software
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+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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+ */
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+
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+#ifndef FFMPEG_ACELP_PITCH_DELAY_H
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+#define FFMPEG_ACELP_PITCH_DELAY_H
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+
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+#include <stdint.h>
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+
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+#define PITCH_DELAY_MIN             20
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+#define PITCH_DELAY_MAX             143
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+
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+/**
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+ * \brief Decode pitch delay of the first subframe encoded by 8 bits with 1/3
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+ *        resolution.
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+ * \param ac_index adaptive codebook index (8 bits)
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+ *
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+ * \return pitch delay in 1/3 units
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+ *
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+ * Pitch delay is coded:
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+ *    with 1/3 resolution, 19  < pitch_delay <  85
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+ *    integers only,       85 <= pitch_delay <= 143
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+ */
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+int ff_acelp_decode_8bit_to_1st_delay3(int ac_index);
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+
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+/**
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+ * \brief Decode pitch delay of the second subframe encoded by 5 or 6 bits
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+ *        with 1/3 precision.
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+ * \param ac_index adaptive codebook index (5 or 6 bits)
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+ * \param pitch_delay_min lower bound (integer) of pitch delay interval
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+ *                      for second subframe
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+ *
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+ * \return pitch delay in 1/3 units
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+ *
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+ * Pitch delay is coded:
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+ *    with 1/3 resolution, -6 < pitch_delay - int(prev_pitch_delay) < 5
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+ *
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+ * \remark The routine is used in G.729 @8k, AMR @10.2k, AMR @7.95k,
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+ *         AMR @7.4k for the second subframe.
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+ */
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+int ff_acelp_decode_5_6_bit_to_2nd_delay3(
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+        int ac_index,
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+        int pitch_delay_min);
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+
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+/**
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+ * \brief Decode pitch delay with 1/3 precision.
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+ * \param ac_index adaptive codebook index (4 bits)
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+ * \param pitch_delay_min lower bound (integer) of pitch delay interval for
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+ *                      second subframe
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+ *
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+ * \return pitch delay in 1/3 units
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+ *
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+ * Pitch delay is coded:
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+ *    integers only,          -6  < pitch_delay - int(prev_pitch_delay) <= -2
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+ *    with 1/3 resolution,    -2  < pitch_delay - int(prev_pitch_delay) <  1
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+ *    integers only,           1 <= pitch_delay - int(prev_pitch_delay) <  5
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+ *
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+ * \remark The routine is used in G.729 @6.4k, AMR @6.7k, AMR @5.9k,
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+ *         AMR @5.15k, AMR @4.75k for the second subframe.
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+ */
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+int ff_acelp_decode_4bit_to_2nd_delay3(
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+        int ac_index,
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+        int pitch_delay_min);
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+
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+/**
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+ * \brief Decode pitch delay of the first subframe encoded by 9 bits
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+ *        with 1/6 precision.
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+ * \param ac_index adaptive codebook index (9 bits)
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+ * \param pitch_delay_min lower bound (integer) of pitch delay interval for
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+ *                      second subframe
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+ *
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+ * \return pitch delay in 1/6 units
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+ *
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+ * Pitch delay is coded:
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+ *    with 1/6 resolution,  17  < pitch_delay <  95
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+ *    integers only,        95 <= pitch_delay <= 143
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+ *
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+ * \remark The routine is used in AMR @12.2k for the first and third subframes.
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+ */
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+int ff_acelp_decode_9bit_to_1st_delay6(int ac_index);
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+
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+/**
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+ * \brief Decode pitch delay of the second subframe encoded by 6 bits
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+ *        with 1/6 precision.
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+ * \param ac_index adaptive codebook index (6 bits)
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+ * \param pitch_delay_min lower bound (integer) of pitch delay interval for
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+ *                      second subframe
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+ *
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+ * \return pitch delay in 1/6 units
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+ *
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+ * Pitch delay is coded:
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+ *    with 1/6 resolution, -6 < pitch_delay - int(prev_pitch_delay) < 5
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+ *
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+ * \remark The routine is used in AMR @12.2k for the second and fourth subframes.
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+ */
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+int ff_acelp_decode_6bit_to_2nd_delay6(
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+        int ac_index,
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+        int pitch_delay_min);
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+
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+/**
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+ * \brief Update past quantized energies
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+ * \param quant_energy [in/out] past quantized energies (5.10)
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+ * \param gain_corr_factor gain correction factor
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+ * \param log2_ma_pred_order log2() of MA prediction order
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+ * \param erasure frame erasure flag
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+ *
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+ * If frame erasure flag is not equal to zero, memory is updated with
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+ * averaged energy, attenuated by 4dB:
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+ *     max(avg(quant_energy[i])-4, -14), i=0,ma_pred_order
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+ *
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+ * In normal mode memory is updated with
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+ *     Er - Ep = 20 * log10(gain_corr_factor)
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+ *
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+ * \remark The routine is used in G.729 and AMR (all modes).
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+ */
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+void ff_acelp_update_past_gain(
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+        int16_t* quant_energy,
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+        int gain_corr_factor,
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+        int log2_ma_pred_order,
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+        int erasure);
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+
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+/**
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+ * \brief Decode the adaptive codebook gain and add
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+ *        correction (4.1.5 and 3.9.1 of G.729).
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+ * \param gain_corr_factor gain correction factor (2.13)
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+ * \param fc_v fixed-codebook vector (2.13)
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+ * \param mr_energy mean innovation energy and fixed-point correction (7.13)
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+ * \param quant_energy [in/out] past quantized energies (5.10)
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+ * \param subframe_size length of subframe
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+ * \param ma_pred_order MA prediction order
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+ *
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+ * \return quantized fixed-codebook gain (14.1)
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+ *
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+ * The routine implements equations 69, 66 and 71 of the G.729 specification (3.9.1)
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+ *
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+ *    Em   - mean innovation energy (dB, constant, depends on decoding algorithm)
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+ *    Ep   - mean-removed predicted energy (dB)
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+ *    Er   - mean-removed innovation energy (dB)
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+ *    Ei   - mean energy of the fixed-codebook contribution (dB)
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+ *    N    - subframe_size
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+ *    M    - MA (Moving Average) prediction order
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+ *    gc   - fixed-codebook gain
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+ *    gc_p - predicted fixed-codebook gain
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+ *
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+ *    Fixed codebook gain is computed using predicted gain gc_p and
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+ *    correction factor gain_corr_factor as shown below:
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+ *
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+ *        gc = gc_p * gain_corr_factor
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+ *
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+ *    The predicted fixed codebook gain gc_p is found by predicting
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+ *    the energy of the fixed-codebook contribution from the energy
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+ *    of previous fixed-codebook contributions.
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+ *
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+ *        mean = 1/N * sum(i,0,N){ fc_v[i] * fc_v[i] }
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+ *
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+ *        Ei = 10log(mean)
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+ *
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+ *        Er = 10log(1/N * gc^2 * mean) - Em = 20log(gc) + Ei - Em
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+ *
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+ *    Replacing Er with Ep and gc with gc_p we will receive:
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+ *
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+ *        Ep = 10log(1/N * gc_p^2 * mean) - Em = 20log(gc_p) + Ei - Em
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+ *
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+ *    and from above:
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+ *
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+ *        gc_p = 10^((Ep - Ei + Em) / 20)
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+ *
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+ *    Ep is predicted using past energies and prediction coefficients:
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+ *
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+ *        Ep = sum(i,0,M){ ma_prediction_coeff[i] * quant_energy[i] }
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+ *
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+ *    gc_p in fixed-point arithmetic is calculated as following:
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+ *
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+ *        mean = 1/N * sum(i,0,N){ (fc_v[i] / 2^13) * (fc_v[i] / 2^13) } =
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+ *        = 1/N * sum(i,0,N) { fc_v[i] * fc_v[i] } / 2^26
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+ *
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+ *        Ei = 10log(mean) = -10log(N) - 10log(2^26) +
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+ *        + 10log(sum(i,0,N) { fc_v[i] * fc_v[i] })
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+ *
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+ *        Ep - Ei + Em = Ep + Em + 10log(N) + 10log(2^26) -
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+ *        - 10log(sum(i,0,N) { fc_v[i] * fc_v[i] }) =
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+ *        = Ep + mr_energy - 10log(sum(i,0,N) { fc_v[i] * fc_v[i] })
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+ *
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+ *        gc_p = 10 ^ ((Ep - Ei + Em) / 20) =
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+ *        = 2 ^ (3.3219 * (Ep - Ei + Em) / 20) = 2 ^ (0.166 * (Ep - Ei + Em))
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+ *
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+ *    where
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+ *
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+ *        mr_energy = Em + 10log(N) + 10log(2^26)
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+ *
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+ * \remark The routine is used in G.729 and AMR (all modes).
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+ */
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+int16_t ff_acelp_decode_gain_code(
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+    int gain_corr_factor,
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+    const int16_t* fc_v,
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+    int mr_energy,
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+    const int16_t* quant_energy,
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+    const int16_t* ma_prediction_coeff,
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+    int subframe_size,
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+    int max_pred_order);
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+
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+#endif /* FFMPEG_ACELP_PITCH_DELAY_H */