EVRC decoder

Signed-off-by: Paul B Mahol <onemda@gmail.com>

1 files changed, 920 insertions, 0 deletions

diff --git a/libavcodec/evrcdec.c b/libavcodec/evrcdec.c
new file mode 100644
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--- /dev/null
+++ b/libavcodec/evrcdec.c
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+/*
+ * Enhanced Variable Rate Codec, Service Option 3 decoder
+ * Copyright (c) 2013 Paul B Mahol
+ *
+ * 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
+ */
+
+/**
+ * @file
+ * Enhanced Variable Rate Codec, Service Option 3 decoder
+ * @author Paul B Mahol
+ */
+
+#include "libavutil/mathematics.h"
+#include "avcodec.h"
+#include "internal.h"
+#include "get_bits.h"
+#include "evrcdata.h"
+#include "acelp_vectors.h"
+#include "lsp.h"
+
+#define MIN_LSP_SEP (0.05 / (2.0 * M_PI))
+#define MIN_DELAY      20
+#define MAX_DELAY     120
+#define NB_SUBFRAMES    3
+#define SUBFRAME_SIZE  54
+#define FILTER_ORDER   10
+#define ACB_SIZE      128
+
+typedef enum {
+    RATE_ERRS = -1,
+    SILENCE,
+    RATE_QUANT,
+    RATE_QUARTER,
+    RATE_HALF,
+    RATE_FULL,
+} evrc_packet_rate;
+
+/**
+ * EVRC-A unpacked data frame
+ */
+typedef struct EVRCAFrame {
+    uint8_t  lpc_flag;        ///< spectral change indicator
+    uint16_t lsp[4];          ///< index into LSP codebook
+    uint8_t  pitch_delay;     ///< pitch delay for entire frame
+    uint8_t  delay_diff;      ///< delay difference for entire frame
+    uint8_t  acb_gain[3];     ///< adaptive codebook gain
+    uint16_t fcb_shape[3][4]; ///< fixed codebook shape
+    uint8_t  fcb_gain[3];     ///< fixed codebook gain index
+    uint8_t  energy_gain;     ///< frame energy gain index
+    uint8_t  tty;             ///< tty baud rate bit
+} EVRCAFrame;
+
+typedef struct EVRCContext {
+    AVFrame          avframe;
+    GetBitContext    gb;
+    evrc_packet_rate bitrate;
+    evrc_packet_rate last_valid_bitrate;
+    EVRCAFrame       frame;
+
+    float            lspf[FILTER_ORDER];
+    float            prev_lspf[FILTER_ORDER];
+    float            synthesis[FILTER_ORDER];
+    float            postfilter_fir[FILTER_ORDER];
+    float            postfilter_iir[FILTER_ORDER];
+    float            postfilter_residual[ACB_SIZE + SUBFRAME_SIZE];
+    float            pitch_delay;
+    float            prev_pitch_delay;
+    float            avg_acb_gain;  ///< average adaptive codebook gain
+    float            avg_fcb_gain;  ///< average fixed codebook gain
+    float            pitch[ACB_SIZE + FILTER_ORDER + SUBFRAME_SIZE];
+    float            pitch_back[ACB_SIZE];
+    float            interpolation_coeffs[136];
+    float            energy_vector[NB_SUBFRAMES];
+    float            fade_scale;
+    float            last;
+
+    uint8_t          prev_energy_gain;
+    uint8_t          prev_error_flag;
+    uint8_t          warned_buf_mismatch_bitrate;
+} EVRCContext;
+
+/**
+ * Frame unpacking for RATE_FULL, RATE_HALF and RATE_QUANT
+ *
+ * @param e the context
+ *
+ * TIA/IS-127 Table 4.21-1
+ */
+static void unpack_frame(EVRCContext *e)
+{
+    EVRCAFrame *frame = &e->frame;
+    GetBitContext *gb = &e->gb;
+
+    switch (e->bitrate) {
+    case RATE_FULL:
+        frame->lpc_flag        = get_bits1(gb);
+        frame->lsp[0]          = get_bits(gb,  6);
+        frame->lsp[1]          = get_bits(gb,  6);
+        frame->lsp[2]          = get_bits(gb,  9);
+        frame->lsp[3]          = get_bits(gb,  7);
+        frame->pitch_delay     = get_bits(gb,  7);
+        frame->delay_diff      = get_bits(gb,  5);
+        frame->acb_gain[0]     = get_bits(gb,  3);
+        frame->fcb_shape[0][0] = get_bits(gb,  8);
+        frame->fcb_shape[0][1] = get_bits(gb,  8);
+        frame->fcb_shape[0][2] = get_bits(gb,  8);
+        frame->fcb_shape[0][3] = get_bits(gb, 11);
+        frame->fcb_gain[0]     = get_bits(gb,  5);
+        frame->acb_gain[1]     = get_bits(gb,  3);
+        frame->fcb_shape[1][0] = get_bits(gb,  8);
+        frame->fcb_shape[1][1] = get_bits(gb,  8);
+        frame->fcb_shape[1][2] = get_bits(gb,  8);
+        frame->fcb_shape[1][3] = get_bits(gb, 11);
+        frame->fcb_gain    [1] = get_bits(gb,  5);
+        frame->acb_gain    [2] = get_bits(gb,  3);
+        frame->fcb_shape[2][0] = get_bits(gb,  8);
+        frame->fcb_shape[2][1] = get_bits(gb,  8);
+        frame->fcb_shape[2][2] = get_bits(gb,  8);
+        frame->fcb_shape[2][3] = get_bits(gb, 11);
+        frame->fcb_gain    [2] = get_bits(gb,  5);
+        frame->tty             = get_bits1(gb);
+        break;
+    case RATE_HALF:
+        frame->lsp         [0] = get_bits(gb,  7);
+        frame->lsp         [1] = get_bits(gb,  7);
+        frame->lsp         [2] = get_bits(gb,  8);
+        frame->pitch_delay     = get_bits(gb,  7);
+        frame->acb_gain    [0] = get_bits(gb,  3);
+        frame->fcb_shape[0][0] = get_bits(gb, 10);
+        frame->fcb_gain    [0] = get_bits(gb,  4);
+        frame->acb_gain    [1] = get_bits(gb,  3);
+        frame->fcb_shape[1][0] = get_bits(gb, 10);
+        frame->fcb_gain    [1] = get_bits(gb,  4);
+        frame->acb_gain    [2] = get_bits(gb,  3);
+        frame->fcb_shape[2][0] = get_bits(gb, 10);
+        frame->fcb_gain    [2] = get_bits(gb,  4);
+        break;
+    case RATE_QUANT:
+        frame->lsp         [0] = get_bits(gb, 4);
+        frame->lsp         [1] = get_bits(gb, 4);
+        frame->energy_gain     = get_bits(gb, 8);
+        break;
+    }
+}
+
+static evrc_packet_rate buf_size2bitrate(const int buf_size)
+{
+    switch (buf_size) {
+    case 23: return RATE_FULL;
+    case 11: return RATE_HALF;
+    case  6: return RATE_QUARTER;
+    case  3: return RATE_QUANT;
+    case  1: return SILENCE;
+    }
+
+    return RATE_ERRS;
+}
+
+/**
+ * Determine the bitrate from the frame size and/or the first byte of the frame.
+ *
+ * @param avctx the AV codec context
+ * @param buf_size length of the buffer
+ * @param buf the bufffer
+ *
+ * @return the bitrate on success,
+ *         RATE_ERRS  if the bitrate cannot be satisfactorily determined
+ */
+static evrc_packet_rate determine_bitrate(AVCodecContext *avctx,
+                                          int *buf_size,
+                                          const uint8_t **buf)
+{
+    evrc_packet_rate bitrate;
+
+    if ((bitrate = buf_size2bitrate(*buf_size)) >= 0) {
+        if (bitrate > **buf) {
+            EVRCContext *e = avctx->priv_data;
+            if (!e->warned_buf_mismatch_bitrate) {
+                av_log(avctx, AV_LOG_WARNING,
+                       "Claimed bitrate and buffer size mismatch.\n");
+                e->warned_buf_mismatch_bitrate = 1;
+            }
+            bitrate = **buf;
+        } else if (bitrate < **buf) {
+            av_log(avctx, AV_LOG_ERROR,
+                   "Buffer is too small for the claimed bitrate.\n");
+            return RATE_ERRS;
+        }
+        (*buf)++;
+        *buf_size -= 1;
+    } else if ((bitrate = buf_size2bitrate(*buf_size + 1)) >= 0) {
+        av_log(avctx, AV_LOG_DEBUG,
+               "Bitrate byte is missing, guessing the bitrate from packet size.\n");
+    } else
+        return RATE_ERRS;
+
+    return bitrate;
+}
+
+static void warn_insufficient_frame_quality(AVCodecContext *avctx,
+                                            const char *message)
+{
+    av_log(avctx, AV_LOG_WARNING, "Frame #%d, %s\n",
+           avctx->frame_number, message);
+}
+
+/**
+ * Initialize the speech codec according to the specification.
+ *
+ * TIA/IS-127 5.2
+ */
+static av_cold int evrc_decode_init(AVCodecContext *avctx)
+{
+    EVRCContext *e = avctx->priv_data;
+    int i, n, idx = 0;
+    float denom = 2.0 / (2.0 * 8.0 + 1.0);
+
+    avcodec_get_frame_defaults(&e->avframe);
+    avctx->coded_frame = &e->avframe;
+
+    avctx->channels       = 1;
+    avctx->channel_layout = AV_CH_LAYOUT_MONO;
+    avctx->sample_fmt     = AV_SAMPLE_FMT_FLT;
+
+    for (i = 0; i < FILTER_ORDER; i++) {
+        e->prev_lspf[i] = (i + 1) * 0.048;
+        e->synthesis[i] = 0.0;
+    }
+
+    for (i = 0; i < ACB_SIZE; i++)
+        e->pitch[i] = e->pitch_back[i] = 0.0;
+
+    e->last_valid_bitrate = RATE_QUANT;
+    e->prev_pitch_delay   = 40.0;
+    e->fade_scale         = 1.0;
+    e->prev_error_flag    = 0;
+    e->avg_acb_gain = e->avg_fcb_gain = 0.0;
+
+    for (i = 0; i < 8; i++) {
+        float tt = ((float)i - 8.0 / 2.0) / 8.0;
+
+        for (n = -8; n <= 8; n++, idx++) {
+            float arg1 = M_PI * 0.9 * (tt - n);
+            float arg2 = M_PI * (tt - n);
+
+            e->interpolation_coeffs[idx] = 0.9;
+            if (arg1)
+                e->interpolation_coeffs[idx] *= (0.54 + 0.46 * cos(arg2 * denom)) *
+                                                 sin(arg1) / arg1;
+        }
+    }
+
+    return 0;
+}
+
+/**
+ * Decode the 10 vector quantized line spectral pair frequencies from the LSP
+ * transmission codes of any bitrate and check for badly received packets.
+ *
+ * @param e the context
+ *
+ * @return 0 on success, -1 if the packet is badly received
+ *
+ * TIA/IS-127 5.2.1, 5.7.1
+ */
+static int decode_lspf(EVRCContext *e)
+{
+    const float **codebooks = evrc_lspq_codebooks[e->bitrate];
+    int i, j, k = 0;
+
+    for (i = 0; i < evrc_lspq_nb_codebooks[e->bitrate]; i++) {
+        int row_size = evrc_lspq_codebooks_row_sizes[e->bitrate][i];
+        const float *codebook = codebooks[i];
+
+        for (j = 0; j < row_size; j++)
+            e->lspf[k++] = codebook[e->frame.lsp[i] * row_size + j];
+    }
+
+    // check for monotonic LSPs
+    for (i = 1; i < FILTER_ORDER; i++)
+        if (e->lspf[i] <= e->lspf[i - 1])
+            return -1;
+
+    // check for minimum separation of LSPs at the splits
+    for (i = 0, k = 0; i < evrc_lspq_nb_codebooks[e->bitrate] - 1; i++) {
+        k += evrc_lspq_codebooks_row_sizes[e->bitrate][i];
+        if (e->lspf[k] - e->lspf[k - 1] <= MIN_LSP_SEP)
+            return -1;
+    }
+
+    return 0;
+}
+
+/*
+ * Interpolation of LSP parameters.
+ *
+ * TIA/IS-127 5.2.3.1, 5.7.3.2
+ */
+static void interpolate_lsp(float *ilsp, const float *lsp,
+                            const float *prev, int index)
+{
+    static const float lsp_interpolation_factors[] = { 0.1667, 0.5, 0.8333 };
+    ff_weighted_vector_sumf(ilsp, prev, lsp,
+                            1.0 - lsp_interpolation_factors[index],
+                            lsp_interpolation_factors[index], FILTER_ORDER);
+}
+
+/*
+ * Reconstruction of the delay contour.
+ *
+ * TIA/IS-127 5.2.2.3.2
+ */
+static void interpolate_delay(float *dst, float current, float prev, int index)
+{
+    static const float d_interpolation_factors[] = { 0, 0.3313, 0.6625, 1, 1 };
+    dst[0] = (1.0 - d_interpolation_factors[index    ]) * prev
+                  + d_interpolation_factors[index    ]  * current;
+    dst[1] = (1.0 - d_interpolation_factors[index + 1]) * prev
+                  + d_interpolation_factors[index + 1]  * current;
+    dst[2] = (1.0 - d_interpolation_factors[index + 2]) * prev
+                  + d_interpolation_factors[index + 2]  * current;
+}
+
+/*
+ * Convert the quantized, interpolated line spectral frequencies,
+ * to prediction coefficients.
+ *
+ * TIA/IS-127 5.2.3.2, 4.7.2.2
+ */
+static void decode_predictor_coeffs(const float *ilspf, float *ilpc)
+{
+    double lsp[FILTER_ORDER];
+    float a[FILTER_ORDER / 2 + 1], b[FILTER_ORDER / 2 + 1];
+    float a1[FILTER_ORDER / 2] = { 0 };
+    float a2[FILTER_ORDER / 2] = { 0 };
+    float b1[FILTER_ORDER / 2] = { 0 };
+    float b2[FILTER_ORDER / 2] = { 0 };
+    int i, k;
+
+    ff_acelp_lsf2lspd(lsp, ilspf, FILTER_ORDER);
+
+    for (k = 0; k <= FILTER_ORDER; k++) {
+        a[0] = k < 2 ? 0.25 : 0;
+        b[0] = k < 2 ? k < 1 ? 0.25 : -0.25 : 0;
+
+        for (i = 0; i < FILTER_ORDER / 2; i++) {
+            a[i + 1] = a[i] - 2 * lsp[i * 2    ] * a1[i] + a2[i];
+            b[i + 1] = b[i] - 2 * lsp[i * 2 + 1] * b1[i] + b2[i];
+            a2[i] = a1[i];
+            a1[i] = a[i];
+            b2[i] = b1[i];
+            b1[i] = b[i];
+        }
+
+        if (k)
+            ilpc[k - 1] = 2.0 * (a[FILTER_ORDER / 2] + b[FILTER_ORDER / 2]);
+    }
+}
+
+static void bl_intrp(EVRCContext *e, float *ex, float delay)
+{
+    float *f;
+    int offset, i, coef_idx;
+    int16_t t;
+
+    offset = lrintf(fabs(delay));
+
+    t = (offset - delay + 0.5) * 8.0 + 0.5;
+    if (t == 8) {
+        t = 0;
+        offset--;
+    }
+
+    f = ex - offset - 8;
+
+    coef_idx = t * (2 * 8 + 1);
+
+    ex[0] = 0.0;
+    for (i = 0; i < 2 * 8 + 1; i++)
+        ex[0] += e->interpolation_coeffs[coef_idx + i] * f[i];
+}
+
+/*
+ * Adaptive codebook excitation.
+ *
+ * TIA/IS-127 5.2.2.3.3, 4.12.5.2
+ */
+static void acb_excitation(EVRCContext *e, float *excitation, float gain,
+                           const float delay[3], int length)
+{
+    float denom, locdelay, dpr, invl;
+    int i;
+
+    invl = 1.0 / ((float) length);
+    dpr = length;
+
+    /* first at-most extra samples */
+    denom = (delay[1] - delay[0]) * invl;
+    for (i = 0; i < dpr; i++) {
+        locdelay = delay[0] + i * denom;
+        bl_intrp(e, excitation + i, locdelay);
+    }
+
+    denom = (delay[2] - delay[1]) * invl;
+    /* interpolation */
+    for (i = dpr; i < dpr + 10; i++) {
+        locdelay = delay[1] + (i - dpr) * denom;
+        bl_intrp(e, excitation + i, locdelay);
+    }
+
+    for (i = 0; i < length; i++)
+        excitation[i] *= gain;
+}
+
+static void decode_8_pulses_35bits(const uint16_t *fixed_index, float *cod)
+{
+    int i, pos1, pos2, offset;
+
+    offset = (fixed_index[3] >> 9) & 3;
+
+    for (i = 0; i < 3; i++) {
+        pos1 = ((fixed_index[i] & 0x7f) / 11) * 5 + ((i + offset) % 5);
+        pos2 = ((fixed_index[i] & 0x7f) % 11) * 5 + ((i + offset) % 5);
+
+        cod[pos1] = (fixed_index[i] & 0x80) ? -1.0 : 1.0;
+
+        if (pos2 < pos1)
+            cod[pos2]  = -cod[pos1];
+        else
+            cod[pos2] +=  cod[pos1];
+    }
+
+    pos1 = ((fixed_index[3] & 0x7f) / 11) * 5 + ((3 + offset) % 5);
+    pos2 = ((fixed_index[3] & 0x7f) % 11) * 5 + ((4 + offset) % 5);
+
+    cod[pos1] = (fixed_index[3] & 0x100) ? -1.0 : 1.0;
+    cod[pos2] = (fixed_index[3] & 0x80 ) ? -1.0 : 1.0;
+}
+
+static void decode_3_pulses_10bits(uint16_t fixed_index, float *cod)
+{
+    float sign;
+    int pos;
+
+    sign = (fixed_index & 0x200) ? -1.0 : 1.0;
+
+    pos = ((fixed_index        & 0x7) * 7) + 4;
+    cod[pos] += sign;
+    pos = (((fixed_index >> 3) & 0x7) * 7) + 2;
+    cod[pos] -= sign;
+    pos = (((fixed_index >> 6) & 0x7) * 7);
+    cod[pos] += sign;
+}
+
+/*
+ * Reconstruction of ACELP fixed codebook excitation for full and half rate.
+ *
+ * TIA/IS-127 5.2.3.7
+ */
+static void fcb_excitation(EVRCContext *e, const uint16_t *codebook,
+                           float *excitation, float pitch_gain,
+                           int pitch_lag, int subframe_size)
+{
+    int i;
+
+    if (e->bitrate == RATE_FULL)
+        decode_8_pulses_35bits(codebook, excitation);
+    else
+        decode_3_pulses_10bits(*codebook, excitation);
+
+    pitch_gain = av_clipf(pitch_gain, 0.2, 0.9);
+
+    for (i = pitch_lag; i < subframe_size; i++)
+        excitation[i] += pitch_gain * excitation[i - pitch_lag];
+}
+
+/**
+ * Synthesis of the decoder output signal.
+ *
+ * param[in]     in              input signal
+ * param[in]     filter_coeffs   LPC coefficients
+ * param[in/out] memory          synthesis filter memory
+ * param         buffer_length   amount of data to process
+ * param[out]    samples         output samples
+ *
+ * TIA/IS-127 5.2.3.15, 5.7.3.4
+ */
+static void synthesis_filter(const float *in, const float *filter_coeffs,
+                             float *memory, int buffer_length, float *samples)
+{
+    int i, j;
+
+    for (i = 0; i < buffer_length; i++) {
+        samples[i] = in[i];
+        for (j = FILTER_ORDER - 1; j > 0; j--) {
+            samples[i] -= filter_coeffs[j] * memory[j];
+            memory[j]   = memory[j - 1];
+        }
+        samples[i] -= filter_coeffs[0] * memory[0];
+        memory[0]   = samples[i];
+    }
+}
+
+static void bandwidth_expansion(float *coeff, const float *inbuf, float gamma)
+{
+    double fac = gamma;
+    int i;
+
+    for (i = 0; i < FILTER_ORDER; i++) {
+        coeff[i] = inbuf[i] * fac;
+        fac *= gamma;
+    }
+}
+
+static void residual_filter(float *output, const float *input,
+                            const float *coef, float *memory, int length)
+{
+    float sum;
+    int i, j;
+
+    for (i = 0; i < length; i++) {
+        sum = input[i];
+
+        for (j = FILTER_ORDER - 1; j > 0; j--) {
+            sum      += coef[j] * memory[j];
+            memory[j] = memory[j - 1];
+        }
+        sum += coef[0] * memory[0];
+        memory[0] = input[i];
+        output[i] = sum;
+    }
+}
+
+/*
+ * TIA/IS-127 Table 5.9.1-1.
+ */
+static const struct PfCoeff {
+    float tilt;
+    float ltgain;
+    float p1;
+    float p2;
+} postfilter_coeffs[5] = {
+    { 0.0 , 0.0 , 0.0 , 0.0  },
+    { 0.0 , 0.0 , 0.57, 0.57 },
+    { 0.0 , 0.0 , 0.0 , 0.0  },
+    { 0.35, 0.50, 0.50, 0.75 },
+    { 0.20, 0.50, 0.57, 0.75 },
+};
+
+/*
+ * Adaptive postfilter.
+ *
+ * TIA/IS-127 5.9
+ */
+static void postfilter(EVRCContext *e, float *in, const float *coeff,
+                       float *out, int idx, const struct PfCoeff *pfc,
+                       int length)
+{
+    float wcoef1[FILTER_ORDER], wcoef2[FILTER_ORDER],
+          scratch[SUBFRAME_SIZE], temp[SUBFRAME_SIZE],
+          mem[SUBFRAME_SIZE];
+    float sum1 = 0.0, sum2 = 0.0, gamma, gain;
+    float tilt = pfc->tilt;
+    int i, n, best;
+
+    bandwidth_expansion(wcoef1, coeff, pfc->p1);
+    bandwidth_expansion(wcoef2, coeff, pfc->p2);
+
+    /* Tilt compensation filter, TIA/IS-127 5.9.1 */
+    for (i = 0; i < length - 1; i++)
+        sum2 += in[i] * in[i + 1];
+    if (sum2 < 0.0)
+        tilt = 0.0;
+
+    for (i = 0; i < length; i++) {
+        scratch[i] = in[i] - tilt * e->last;
+        e->last = in[i];
+    }
+
+    /* Short term residual filter, TIA/IS-127 5.9.2 */
+    residual_filter(&e->postfilter_residual[ACB_SIZE], scratch, wcoef1, e->postfilter_fir, length);
+
+    /* Long term postfilter */
+    best = idx;
+    for (i = FFMIN(MIN_DELAY, idx - 3); i <= FFMAX(MAX_DELAY, idx + 3); i++) {
+        for (n = ACB_SIZE, sum2 = 0; n < ACB_SIZE + length; n++)
+            sum2 += e->postfilter_residual[n] * e->postfilter_residual[n - i];
+        if (sum2 > sum1) {
+            sum1 = sum2;
+            best = i;
+        }
+    }
+
+    for (i = ACB_SIZE, sum1 = 0; i < ACB_SIZE + length; i++)
+        sum1 += e->postfilter_residual[i - best] * e->postfilter_residual[i - best];
+    for (i = ACB_SIZE, sum2 = 0; i < ACB_SIZE + length; i++)
+        sum2 += e->postfilter_residual[i] * e->postfilter_residual[i - best];
+
+    if (sum2 * sum1 == 0 || e->bitrate == RATE_QUANT) {
+        memcpy(temp, e->postfilter_residual + ACB_SIZE, length * sizeof(float));
+    } else {
+        gamma = sum2 / sum1;
+        if (gamma < 0.5)
+            memcpy(temp, e->postfilter_residual + ACB_SIZE, length * sizeof(float));
+        else {
+            gamma = FFMIN(gamma, 1.0);
+
+            for (i = 0; i < length; i++) {
+                temp[i] = e->postfilter_residual[ACB_SIZE + i] + gamma *
+                    pfc->ltgain * e->postfilter_residual[ACB_SIZE + i - best];
+            }
+        }
+    }
+
+    memcpy(scratch, temp, length * sizeof(float));
+    memcpy(mem, e->postfilter_iir, FILTER_ORDER * sizeof(float));
+    synthesis_filter(scratch, wcoef2, mem, length, scratch);
+
+    /* Gain computation, TIA/IS-127 5.9.4-2 */
+    for (i = 0, sum1 = 0, sum2 = 0; i < length; i++) {
+        sum1 += in[i] * in[i];
+        sum2 += scratch[i] * scratch[i];
+    }
+    gain = sum2 ? sqrt(sum1 / sum2) : 1.0;
+
+    for (i = 0; i < length; i++)
+        temp[i] *= gain;
+
+    /* Short term postfilter */
+    synthesis_filter(temp, wcoef2, e->postfilter_iir, length, out);
+
+    memcpy(e->postfilter_residual,
+           e->postfilter_residual + length, ACB_SIZE * sizeof(float));
+}
+
+static void frame_erasure(EVRCContext *e, float *samples)
+{
+    float ilspf[FILTER_ORDER], ilpc[FILTER_ORDER], idelay[NB_SUBFRAMES],
+          tmp[SUBFRAME_SIZE + 6], f;
+    int i, j;
+
+    for (i = 0; i < FILTER_ORDER; i++) {
+        if (e->bitrate != RATE_QUANT)
+            e->lspf[i] = e->prev_lspf[i] * 0.875 + 0.125 * (i + 1) * 0.048;
+        else
+            e->lspf[i] = e->prev_lspf[i];
+    }
+
+    if (e->prev_error_flag)
+        e->avg_acb_gain *= 0.75;
+    if (e->bitrate == RATE_FULL)
+        memcpy(e->pitch_back, e->pitch, ACB_SIZE * sizeof(float));
+    if (e->last_valid_bitrate == RATE_QUANT)
+        e->bitrate = RATE_QUANT;
+    else
+        e->bitrate = RATE_FULL;
+
+    if (e->bitrate == RATE_FULL || e->bitrate == RATE_HALF) {
+        e->pitch_delay = e->prev_pitch_delay;
+    } else {
+        float sum = 0;
+
+        idelay[0] = idelay[1] = idelay[2] = MIN_DELAY;
+
+        for (i = 0; i < NB_SUBFRAMES; i++)
+            sum += evrc_energy_quant[e->prev_energy_gain][i];
+        sum /= (float) NB_SUBFRAMES;
+        sum  = pow(10, sum);
+        for (i = 0; i < NB_SUBFRAMES; i++)
+            e->energy_vector[i] = sum;
+    }
+
+    if (fabs(e->pitch_delay - e->prev_pitch_delay) > 15)
+        e->prev_pitch_delay = e->pitch_delay;
+
+    for (i = 0; i < NB_SUBFRAMES; i++) {
+        int subframe_size = subframe_sizes[i];
+        int pitch_lag;
+
+        interpolate_lsp(ilspf, e->lspf, e->prev_lspf, i);
+
+        if (e->bitrate != RATE_QUANT) {
+            if (e->avg_acb_gain < 0.3) {
+                idelay[0] = estimation_delay[i];
+                idelay[1] = estimation_delay[i + 1];
+                idelay[2] = estimation_delay[i + 2];
+            } else {
+                interpolate_delay(idelay, e->pitch_delay, e->prev_pitch_delay, i);
+            }
+        }
+
+        pitch_lag = lrintf((idelay[1] + idelay[0]) / 2.0);
+        decode_predictor_coeffs(ilspf, ilpc);
+
+        if (e->bitrate != RATE_QUANT) {
+            acb_excitation(e, e->pitch + ACB_SIZE,
+                           e->avg_acb_gain, idelay, subframe_size);
+            for (j = 0; j < subframe_size; j++)
+                e->pitch[ACB_SIZE + j] *= e->fade_scale;
+            e->fade_scale = FFMAX(e->fade_scale - 0.05, 0.0);
+        } else {
+            for (j = 0; j < subframe_size; j++)
+                e->pitch[ACB_SIZE + j] = e->energy_vector[i];
+        }
+
+        memcpy(e->pitch, e->pitch + subframe_size, ACB_SIZE * sizeof(float));
+
+        if (e->bitrate != RATE_QUANT && e->avg_acb_gain < 0.4) {
+            f = 0.1 * e->avg_fcb_gain;
+            for (j = 0; j < subframe_size; j++)
+                e->pitch[ACB_SIZE + j] += f;
+        } else if (e->bitrate == RATE_QUANT) {
+            for (j = 0; j < subframe_size; j++)
+                e->pitch[ACB_SIZE + j] = e->energy_vector[i];
+        }
+
+        synthesis_filter(e->pitch + ACB_SIZE, ilpc,
+                         e->synthesis, subframe_size, tmp);
+        postfilter(e, tmp, ilpc, samples, pitch_lag,
+                   &postfilter_coeffs[e->bitrate], subframe_size);
+
+        samples += subframe_size;
+    }
+}
+
+static int evrc_decode_frame(AVCodecContext *avctx, void *data,
+                             int *got_frame_ptr, AVPacket *avpkt)
+{
+    const uint8_t *buf = avpkt->data;
+    EVRCContext *e     = avctx->priv_data;
+    int buf_size       = avpkt->size;
+    float ilspf[FILTER_ORDER], ilpc[FILTER_ORDER], idelay[NB_SUBFRAMES];
+    float *samples;
+    int   i, j, ret, error_flag = 0;
+
+    e->avframe.nb_samples = 160;
+    if ((ret = ff_get_buffer(avctx, &e->avframe)) < 0)
+        return ret;
+    samples = (float *)e->avframe.data[0];
+
+    if ((e->bitrate = determine_bitrate(avctx, &buf_size, &buf)) == RATE_ERRS) {
+        warn_insufficient_frame_quality(avctx, "bitrate cannot be determined.");
+        goto erasure;
+    }
+    if (e->bitrate <= SILENCE || e->bitrate == RATE_QUARTER)
+        goto erasure;
+    if (e->bitrate == RATE_QUANT && e->last_valid_bitrate == RATE_FULL
+                                 && !e->prev_error_flag)
+        goto erasure;
+
+    init_get_bits(&e->gb, buf, 8 * buf_size);
+    memset(&e->frame, 0, sizeof(EVRCAFrame));
+
+    unpack_frame(e);
+
+    if (e->bitrate != RATE_QUANT) {
+        uint8_t *p = (uint8_t *) &e->frame;
+        for (i = 0; i < sizeof(EVRCAFrame); i++) {
+            if (p[i])
+                break;
+        }
+        if (i == sizeof(EVRCAFrame))
+            goto erasure;
+    } else if (e->frame.lsp[0] == e->frame.lsp[1] == 0xf &&
+               e->frame.energy_gain == 0xff) {
+        goto erasure;
+    }
+
+    if (decode_lspf(e) < 0)
+        goto erasure;
+
+    if (e->bitrate == RATE_FULL || e->bitrate == RATE_HALF) {
+        /* Pitch delay parameter checking as per TIA/IS-127 5.1.5.1 */
+        if (e->frame.pitch_delay > MAX_DELAY - MIN_DELAY)
+            goto erasure;
+
+        e->pitch_delay = e->frame.pitch_delay + MIN_DELAY;
+
+        /* Delay diff parameter checking as per TIA/IS-127 5.1.5.2 */
+        if (e->frame.delay_diff) {
+            int p = e->pitch_delay - e->frame.delay_diff + 16;
+            if (p < MIN_DELAY || p > MAX_DELAY)
+                goto erasure;
+        }
+
+        /* Delay contour reconstruction as per TIA/IS-127 5.2.2.2 */
+        if (e->frame.delay_diff &&
+            e->bitrate == RATE_FULL && e->prev_error_flag) {
+            float delay;
+
+            memcpy(e->pitch, e->pitch_back, ACB_SIZE * sizeof(float));
+
+            delay = e->prev_pitch_delay;
+            e->prev_pitch_delay = delay - e->frame.delay_diff + 16.0;
+
+            if (fabs(e->pitch_delay - delay) > 15)
+                delay = e->pitch_delay;
+
+            for (i = 0; i < NB_SUBFRAMES; i++) {
+                int subframe_size = subframe_sizes[i];
+
+                interpolate_delay(idelay, delay, e->prev_pitch_delay, i);
+                acb_excitation(e, e->pitch + ACB_SIZE, e->avg_acb_gain, idelay, subframe_size);
+                memcpy(e->pitch, e->pitch + subframe_size, ACB_SIZE * sizeof(float));
+            }
+        }
+
+        /* Smoothing of the decoded delay as per TIA/IS-127 5.2.2.5 */
+        if (fabs(e->pitch_delay - e->prev_pitch_delay) > 15)
+            e->prev_pitch_delay = e->pitch_delay;
+
+        e->avg_acb_gain = e->avg_fcb_gain = 0.0;
+    } else {
+        idelay[0] = idelay[1] = idelay[2] = MIN_DELAY;
+
+        /* Decode frame energy vectors as per TIA/IS-127 5.7.2 */
+        for (i = 0; i < NB_SUBFRAMES; i++)
+            e->energy_vector[i] = pow(10, evrc_energy_quant[e->frame.energy_gain][i]);
+        e->prev_energy_gain = e->frame.energy_gain;
+    }
+
+    for (i = 0; i < NB_SUBFRAMES; i++) {
+        float tmp[SUBFRAME_SIZE + 6] = { 0 };
+        int subframe_size = subframe_sizes[i];
+        int pitch_lag;
+
+        interpolate_lsp(ilspf, e->lspf, e->prev_lspf, i);
+
+        if (e->bitrate != RATE_QUANT)
+            interpolate_delay(idelay, e->pitch_delay, e->prev_pitch_delay, i);
+
+        pitch_lag = lrintf((idelay[1] + idelay[0]) / 2.0);
+        decode_predictor_coeffs(ilspf, ilpc);
+
+        /* Bandwidth expansion as per TIA/IS-127 5.2.3.3 */
+        if (e->frame.lpc_flag && e->prev_error_flag)
+            bandwidth_expansion(ilpc, ilpc, 0.75);
+
+        if (e->bitrate != RATE_QUANT) {
+            float acb_sum, f;
+
+            f = exp((e->bitrate == RATE_HALF ? 0.5 : 0.25)
+                         * (e->frame.fcb_gain[i] + 1));
+            acb_sum = pitch_gain_vq[e->frame.acb_gain[i]];
+            e->avg_acb_gain += acb_sum / NB_SUBFRAMES;
+            e->avg_fcb_gain += f / NB_SUBFRAMES;
+
+            acb_excitation(e, e->pitch + ACB_SIZE,
+                           acb_sum, idelay, subframe_size);
+            fcb_excitation(e, e->frame.fcb_shape[i], tmp,
+                           acb_sum, pitch_lag, subframe_size);
+
+            /* Total excitation generation as per TIA/IS-127 5.2.3.9 */
+            for (j = 0; j < subframe_size; j++)
+                e->pitch[ACB_SIZE + j] += f * tmp[j];
+            e->fade_scale = FFMIN(e->fade_scale + 0.2, 1.0);
+        } else {
+            for (j = 0; j < subframe_size; j++)
+                e->pitch[ACB_SIZE + j] = e->energy_vector[i];
+        }
+
+        memcpy(e->pitch, e->pitch + subframe_size, ACB_SIZE * sizeof(float));
+
+        synthesis_filter(e->pitch + ACB_SIZE, ilpc,
+                         e->synthesis, subframe_size, tmp);
+        postfilter(e, tmp, ilpc, samples, pitch_lag,
+                   &postfilter_coeffs[e->bitrate], subframe_size);
+
+        samples += subframe_size;
+    }
+
+    if (error_flag) {
+erasure:
+        error_flag = 1;
+        av_log(avctx, AV_LOG_WARNING, "frame erasure\n");
+        frame_erasure(e, samples);
+    }
+
+    memcpy(e->prev_lspf, e->lspf, sizeof(e->prev_lspf));
+    e->prev_error_flag    = error_flag;
+    e->last_valid_bitrate = e->bitrate;
+
+    if (e->bitrate != RATE_QUANT)
+        e->prev_pitch_delay = e->pitch_delay;
+
+    samples = (float *)e->avframe.data[0];
+    for (i = 0; i < 160; i++)
+        samples[i] /= 32768;
+
+    *got_frame_ptr   = 1;
+    *(AVFrame *)data = e->avframe;
+
+    return avpkt->size;
+}
+
+AVCodec ff_evrc_decoder = {
+    .name           = "evrc",
+    .type           = AVMEDIA_TYPE_AUDIO,
+    .id             = AV_CODEC_ID_EVRC,
+    .init           = evrc_decode_init,
+    .decode         = evrc_decode_frame,
+    .capabilities   = CODEC_CAP_DR1,
+    .priv_data_size = sizeof(EVRCContext),
+    .long_name      = NULL_IF_CONFIG_SMALL("EVRC (Enhanced Variable Rate Codec)"),
+};