gain code, gain pitch and pitch delay decoding for ACELP based codecs

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

1 files changed, 220 insertions, 0 deletions

diff --git a/libavcodec/acelp_pitch_delay.h b/libavcodec/acelp_pitch_delay.h
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+/*
+ * gain code, gain pitch and pitch delay decoding
+ *
+ * Copyright (c) 2008 Vladimir Voroshilov
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg 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.
+ *
+ * FFmpeg 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 Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef FFMPEG_ACELP_PITCH_DELAY_H
+#define FFMPEG_ACELP_PITCH_DELAY_H
+
+#include <stdint.h>
+
+#define PITCH_DELAY_MIN             20
+#define PITCH_DELAY_MAX             143
+
+/**
+ * \brief Decode pitch delay of the first subframe encoded by 8 bits with 1/3
+ *        resolution.
+ * \param ac_index adaptive codebook index (8 bits)
+ *
+ * \return pitch delay in 1/3 units
+ *
+ * Pitch delay is coded:
+ *    with 1/3 resolution, 19  < pitch_delay <  85
+ *    integers only,       85 <= pitch_delay <= 143
+ */
+int ff_acelp_decode_8bit_to_1st_delay3(int ac_index);
+
+/**
+ * \brief Decode pitch delay of the second subframe encoded by 5 or 6 bits
+ *        with 1/3 precision.
+ * \param ac_index adaptive codebook index (5 or 6 bits)
+ * \param pitch_delay_min lower bound (integer) of pitch delay interval
+ *                      for second subframe
+ *
+ * \return pitch delay in 1/3 units
+ *
+ * Pitch delay is coded:
+ *    with 1/3 resolution, -6 < pitch_delay - int(prev_pitch_delay) < 5
+ *
+ * \remark The routine is used in G.729 @8k, AMR @10.2k, AMR @7.95k,
+ *         AMR @7.4k for the second subframe.
+ */
+int ff_acelp_decode_5_6_bit_to_2nd_delay3(
+        int ac_index,
+        int pitch_delay_min);
+
+/**
+ * \brief Decode pitch delay with 1/3 precision.
+ * \param ac_index adaptive codebook index (4 bits)
+ * \param pitch_delay_min lower bound (integer) of pitch delay interval for
+ *                      second subframe
+ *
+ * \return pitch delay in 1/3 units
+ *
+ * Pitch delay is coded:
+ *    integers only,          -6  < pitch_delay - int(prev_pitch_delay) <= -2
+ *    with 1/3 resolution,    -2  < pitch_delay - int(prev_pitch_delay) <  1
+ *    integers only,           1 <= pitch_delay - int(prev_pitch_delay) <  5
+ *
+ * \remark The routine is used in G.729 @6.4k, AMR @6.7k, AMR @5.9k,
+ *         AMR @5.15k, AMR @4.75k for the second subframe.
+ */
+int ff_acelp_decode_4bit_to_2nd_delay3(
+        int ac_index,
+        int pitch_delay_min);
+
+/**
+ * \brief Decode pitch delay of the first subframe encoded by 9 bits
+ *        with 1/6 precision.
+ * \param ac_index adaptive codebook index (9 bits)
+ * \param pitch_delay_min lower bound (integer) of pitch delay interval for
+ *                      second subframe
+ *
+ * \return pitch delay in 1/6 units
+ *
+ * Pitch delay is coded:
+ *    with 1/6 resolution,  17  < pitch_delay <  95
+ *    integers only,        95 <= pitch_delay <= 143
+ *
+ * \remark The routine is used in AMR @12.2k for the first and third subframes.
+ */
+int ff_acelp_decode_9bit_to_1st_delay6(int ac_index);
+
+/**
+ * \brief Decode pitch delay of the second subframe encoded by 6 bits
+ *        with 1/6 precision.
+ * \param ac_index adaptive codebook index (6 bits)
+ * \param pitch_delay_min lower bound (integer) of pitch delay interval for
+ *                      second subframe
+ *
+ * \return pitch delay in 1/6 units
+ *
+ * Pitch delay is coded:
+ *    with 1/6 resolution, -6 < pitch_delay - int(prev_pitch_delay) < 5
+ *
+ * \remark The routine is used in AMR @12.2k for the second and fourth subframes.
+ */
+int ff_acelp_decode_6bit_to_2nd_delay6(
+        int ac_index,
+        int pitch_delay_min);
+
+/**
+ * \brief Update past quantized energies
+ * \param quant_energy [in/out] past quantized energies (5.10)
+ * \param gain_corr_factor gain correction factor
+ * \param log2_ma_pred_order log2() of MA prediction order
+ * \param erasure frame erasure flag
+ *
+ * If frame erasure flag is not equal to zero, memory is updated with
+ * averaged energy, attenuated by 4dB:
+ *     max(avg(quant_energy[i])-4, -14), i=0,ma_pred_order
+ *
+ * In normal mode memory is updated with
+ *     Er - Ep = 20 * log10(gain_corr_factor)
+ *
+ * \remark The routine is used in G.729 and AMR (all modes).
+ */
+void ff_acelp_update_past_gain(
+        int16_t* quant_energy,
+        int gain_corr_factor,
+        int log2_ma_pred_order,
+        int erasure);
+
+/**
+ * \brief Decode the adaptive codebook gain and add
+ *        correction (4.1.5 and 3.9.1 of G.729).
+ * \param gain_corr_factor gain correction factor (2.13)
+ * \param fc_v fixed-codebook vector (2.13)
+ * \param mr_energy mean innovation energy and fixed-point correction (7.13)
+ * \param quant_energy [in/out] past quantized energies (5.10)
+ * \param subframe_size length of subframe
+ * \param ma_pred_order MA prediction order
+ *
+ * \return quantized fixed-codebook gain (14.1)
+ *
+ * The routine implements equations 69, 66 and 71 of the G.729 specification (3.9.1)
+ *
+ *    Em   - mean innovation energy (dB, constant, depends on decoding algorithm)
+ *    Ep   - mean-removed predicted energy (dB)
+ *    Er   - mean-removed innovation energy (dB)
+ *    Ei   - mean energy of the fixed-codebook contribution (dB)
+ *    N    - subframe_size
+ *    M    - MA (Moving Average) prediction order
+ *    gc   - fixed-codebook gain
+ *    gc_p - predicted fixed-codebook gain
+ *
+ *    Fixed codebook gain is computed using predicted gain gc_p and
+ *    correction factor gain_corr_factor as shown below:
+ *
+ *        gc = gc_p * gain_corr_factor
+ *
+ *    The predicted fixed codebook gain gc_p is found by predicting
+ *    the energy of the fixed-codebook contribution from the energy
+ *    of previous fixed-codebook contributions.
+ *
+ *        mean = 1/N * sum(i,0,N){ fc_v[i] * fc_v[i] }
+ *
+ *        Ei = 10log(mean)
+ *
+ *        Er = 10log(1/N * gc^2 * mean) - Em = 20log(gc) + Ei - Em
+ *
+ *    Replacing Er with Ep and gc with gc_p we will receive:
+ *
+ *        Ep = 10log(1/N * gc_p^2 * mean) - Em = 20log(gc_p) + Ei - Em
+ *
+ *    and from above:
+ *
+ *        gc_p = 10^((Ep - Ei + Em) / 20)
+ *
+ *    Ep is predicted using past energies and prediction coefficients:
+ *
+ *        Ep = sum(i,0,M){ ma_prediction_coeff[i] * quant_energy[i] }
+ *
+ *    gc_p in fixed-point arithmetic is calculated as following:
+ *
+ *        mean = 1/N * sum(i,0,N){ (fc_v[i] / 2^13) * (fc_v[i] / 2^13) } =
+ *        = 1/N * sum(i,0,N) { fc_v[i] * fc_v[i] } / 2^26
+ *
+ *        Ei = 10log(mean) = -10log(N) - 10log(2^26) +
+ *        + 10log(sum(i,0,N) { fc_v[i] * fc_v[i] })
+ *
+ *        Ep - Ei + Em = Ep + Em + 10log(N) + 10log(2^26) -
+ *        - 10log(sum(i,0,N) { fc_v[i] * fc_v[i] }) =
+ *        = Ep + mr_energy - 10log(sum(i,0,N) { fc_v[i] * fc_v[i] })
+ *
+ *        gc_p = 10 ^ ((Ep - Ei + Em) / 20) =
+ *        = 2 ^ (3.3219 * (Ep - Ei + Em) / 20) = 2 ^ (0.166 * (Ep - Ei + Em))
+ *
+ *    where
+ *
+ *        mr_energy = Em + 10log(N) + 10log(2^26)
+ *
+ * \remark The routine is used in G.729 and AMR (all modes).
+ */
+int16_t ff_acelp_decode_gain_code(
+    int gain_corr_factor,
+    const int16_t* fc_v,
+    int mr_energy,
+    const int16_t* quant_energy,
+    const int16_t* ma_prediction_coeff,
+    int subframe_size,
+    int max_pred_order);
+
+#endif /* FFMPEG_ACELP_PITCH_DELAY_H */