wmadec.c

ffmpeg的完整源代码和作者自己写的文档。不但有在Linux的工程哦

/*
 * WMA compatible decoder
 * Copyright (c) 2002 The FFmpeg Project.
 *
 * 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 wmadec.c
 * WMA compatible decoder.
 * This decoder handles Microsoft Windows Media Audio data, versions 1 & 2.
 * WMA v1 is identified by audio format 0x160 in Microsoft media files
 * (ASF/AVI/WAV). WMA v2 is identified by audio format 0x161.
 *
 * To use this decoder, a calling application must supply the extra data
 * bytes provided with the WMA data. These are the extra, codec-specific
 * bytes at the end of a WAVEFORMATEX data structure. Transmit these bytes
 * to the decoder using the extradata[_size] fields in AVCodecContext. There
 * should be 4 extra bytes for v1 data and 6 extra bytes for v2 data.
 */

#include "avcodec.h"
#include "wma.h"

#undef NDEBUG
#include <assert.h>

#define EXPVLCBITS 8
#define EXPMAX ((19+EXPVLCBITS-1)/EXPVLCBITS)

#define HGAINVLCBITS 9
#define HGAINMAX ((13+HGAINVLCBITS-1)/HGAINVLCBITS)

static void wma_lsp_to_curve_init(WMACodecContext *s, int frame_len);

#ifdef TRACE
static void dump_shorts(WMACodecContext *s, const char *name, const short *tab, int n)
{
    int i;

    tprintf(s->avctx, "%s[%d]:\n", name, n);
    for(i=0;i<n;i++) {
        if ((i & 7) == 0)
            tprintf(s->avctx, "%4d: ", i);
        tprintf(s->avctx, " %5d.0", tab[i]);
        if ((i & 7) == 7)
            tprintf(s->avctx, "\n");
    }
}

static void dump_floats(WMACodecContext *s, const char *name, int prec, const float *tab, int n)
{
    int i;

    tprintf(s->avctx, "%s[%d]:\n", name, n);
    for(i=0;i<n;i++) {
        if ((i & 7) == 0)
            tprintf(s->avctx, "%4d: ", i);
        tprintf(s->avctx, " %8.*f", prec, tab[i]);
        if ((i & 7) == 7)
            tprintf(s->avctx, "\n");
    }
    if ((i & 7) != 0)
        tprintf(s->avctx, "\n");
}
#endif

static int wma_decode_init(AVCodecContext * avctx)
{
    WMACodecContext *s = avctx->priv_data;
    int i, flags1, flags2;
    uint8_t *extradata;

    s->avctx = avctx;

    /* extract flag infos */
    flags1 = 0;
    flags2 = 0;
    extradata = avctx->extradata;
    if (avctx->codec->id == CODEC_ID_WMAV1 && avctx->extradata_size >= 4) {
        flags1 = AV_RL16(extradata);
        flags2 = AV_RL16(extradata+2);
    } else if (avctx->codec->id == CODEC_ID_WMAV2 && avctx->extradata_size >= 6) {
        flags1 = AV_RL32(extradata);
        flags2 = AV_RL16(extradata+4);
    }
// for(i=0; i<avctx->extradata_size; i++)
//     av_log(NULL, AV_LOG_ERROR, "%02X ", extradata[i]);

    s->use_exp_vlc = flags2 & 0x0001;
    s->use_bit_reservoir = flags2 & 0x0002;
    s->use_variable_block_len = flags2 & 0x0004;

    if(ff_wma_init(avctx, flags2)<0)
        return -1;

    /* init MDCT */
    for(i = 0; i < s->nb_block_sizes; i++)
        ff_mdct_init(&s->mdct_ctx[i], s->frame_len_bits - i + 1, 1);

    if (s->use_noise_coding) {
        init_vlc(&s->hgain_vlc, HGAINVLCBITS, sizeof(ff_wma_hgain_huffbits),
                 ff_wma_hgain_huffbits, 1, 1,
                 ff_wma_hgain_huffcodes, 2, 2, 0);
    }

    if (s->use_exp_vlc) {
        init_vlc(&s->exp_vlc, EXPVLCBITS, sizeof(ff_wma_scale_huffbits), //FIXME move out of context
                 ff_wma_scale_huffbits, 1, 1,
                 ff_wma_scale_huffcodes, 4, 4, 0);
    } else {
        wma_lsp_to_curve_init(s, s->frame_len);
    }

    return 0;
}

/**
 * compute x^-0.25 with an exponent and mantissa table. We use linear
 * interpolation to reduce the mantissa table size at a small speed
 * expense (linear interpolation approximately doubles the number of
 * bits of precision).
 */
static inline float pow_m1_4(WMACodecContext *s, float x)
{
    union {
        float f;
        unsigned int v;
    } u, t;
    unsigned int e, m;
    float a, b;

    u.f = x;
    e = u.v >> 23;
    m = (u.v >> (23 - LSP_POW_BITS)) & ((1 << LSP_POW_BITS) - 1);
    /* build interpolation scale: 1 <= t < 2. */
    t.v = ((u.v << LSP_POW_BITS) & ((1 << 23) - 1)) | (127 << 23);
    a = s->lsp_pow_m_table1[m];
    b = s->lsp_pow_m_table2[m];
    return s->lsp_pow_e_table[e] * (a + b * t.f);
}

static void wma_lsp_to_curve_init(WMACodecContext *s, int frame_len)
{
    float wdel, a, b;
    int i, e, m;

    wdel = M_PI / frame_len;
    for(i=0;i<frame_len;i++)
        s->lsp_cos_table[i] = 2.0f * cos(wdel * i);

    /* tables for x^-0.25 computation */
    for(i=0;i<256;i++) {
        e = i - 126;
        s->lsp_pow_e_table[i] = pow(2.0, e * -0.25);
    }

    /* NOTE: these two tables are needed to avoid two operations in
       pow_m1_4 */
    b = 1.0;
    for(i=(1 << LSP_POW_BITS) - 1;i>=0;i--) {
        m = (1 << LSP_POW_BITS) + i;
        a = (float)m * (0.5 / (1 << LSP_POW_BITS));
        a = pow(a, -0.25);
        s->lsp_pow_m_table1[i] = 2 * a - b;
        s->lsp_pow_m_table2[i] = b - a;
        b = a;
    }
#if 0
    for(i=1;i<20;i++) {
        float v, r1, r2;
        v = 5.0 / i;
        r1 = pow_m1_4(s, v);
        r2 = pow(v,-0.25);
        printf("%f^-0.25=%f e=%f\n", v, r1, r2 - r1);
    }
#endif
}

/**
 * NOTE: We use the same code as Vorbis here
 * @todo optimize it further with SSE/3Dnow
 */
static void wma_lsp_to_curve(WMACodecContext *s,
                             float *out, float *val_max_ptr,
                             int n, float *lsp)
{
    int i, j;
    float p, q, w, v, val_max;

    val_max = 0;
    for(i=0;i<n;i++) {
        p = 0.5f;
        q = 0.5f;
        w = s->lsp_cos_table[i];
        for(j=1;j<NB_LSP_COEFS;j+=2){
            q *= w - lsp[j - 1];
            p *= w - lsp[j];
        }
        p *= p * (2.0f - w);
        q *= q * (2.0f + w);
        v = p + q;
        v = pow_m1_4(s, v);
        if (v > val_max)
            val_max = v;
        out[i] = v;
    }
    *val_max_ptr = val_max;
}

/**
 * decode exponents coded with LSP coefficients (same idea as Vorbis)
 */
static void decode_exp_lsp(WMACodecContext *s, int ch)
{
    float lsp_coefs[NB_LSP_COEFS];
    int val, i;

    for(i = 0; i < NB_LSP_COEFS; i++) {
        if (i == 0 || i >= 8)
            val = get_bits(&s->gb, 3);
        else
            val = get_bits(&s->gb, 4);
        lsp_coefs[i] = ff_wma_lsp_codebook[i][val];
    }

    wma_lsp_to_curve(s, s->exponents[ch], &s->max_exponent[ch],
                     s->block_len, lsp_coefs);
}

/**
 * decode exponents coded with VLC codes
 */
static int decode_exp_vlc(WMACodecContext *s, int ch)
{
    int last_exp, n, code;
    const uint16_t *ptr, *band_ptr;
    float v, *q, max_scale, *q_end;

    band_ptr = s->exponent_bands[s->frame_len_bits - s->block_len_bits];
    ptr = band_ptr;
    q = s->exponents[ch];
    q_end = q + s->block_len;
    max_scale = 0;
    if (s->version == 1) {
        last_exp = get_bits(&s->gb, 5) + 10;
        /* XXX: use a table */
        v = pow(10, last_exp * (1.0 / 16.0));
        max_scale = v;
        n = *ptr++;
        do {
            *q++ = v;
        } while (--n);
    }else
        last_exp = 36;

    while (q < q_end) {
        code = get_vlc2(&s->gb, s->exp_vlc.table, EXPVLCBITS, EXPMAX);
        if (code < 0)
            return -1;
        /* NOTE: this offset is the same as MPEG4 AAC ! */
        last_exp += code - 60;
        /* XXX: use a table */
        v = pow(10, last_exp * (1.0 / 16.0));
        if (v > max_scale)
            max_scale = v;
        n = *ptr++;
        do {
            *q++ = v;
        } while (--n);
    }
    s->max_exponent[ch] = max_scale;
    return 0;
}


/**
 * Apply MDCT window and add into output.
 *
 * We ensure that when the windows overlap their squared sum
 * is always 1 (MDCT reconstruction rule).
 */
static void wma_window(WMACodecContext *s, float *out)
{
    float *in = s->output;
    int block_len, bsize, n;

    /* left part */
    if (s->block_len_bits <= s->prev_block_len_bits) {
        block_len = s->block_len;
        bsize = s->frame_len_bits - s->block_len_bits;

        s->dsp.vector_fmul_add_add(out, in, s->windows[bsize],
                                   out, 0, block_len, 1);

    } else {
        block_len = 1 << s->prev_block_len_bits;
        n = (s->block_len - block_len) / 2;
        bsize = s->frame_len_bits - s->prev_block_len_bits;

        s->dsp.vector_fmul_add_add(out+n, in+n, s->windows[bsize],
                                   out+n, 0, block_len, 1);

        memcpy(out+n+block_len, in+n+block_len, n*sizeof(float));
    }

    out += s->block_len;
    in += s->block_len;

    /* right part */
    if (s->block_len_bits <= s->next_block_len_bits) {
        block_len = s->block_len;
        bsize = s->frame_len_bits - s->block_len_bits;

        s->dsp.vector_fmul_reverse(out, in, s->windows[bsize], block_len);

    } else {
        block_len = 1 << s->next_block_len_bits;
        n = (s->block_len - block_len) / 2;
        bsize = s->frame_len_bits - s->next_block_len_bits;

        memcpy(out, in, n*sizeof(float));

        s->dsp.vector_fmul_reverse(out+n, in+n, s->windows[bsize], block_len);

        memset(out+n+block_len, 0, n*sizeof(float));
    }
}


/**
 * @return 0 if OK. 1 if last block of frame. return -1 if
 * unrecorrable error.
 */
static int wma_decode_block(WMACodecContext *s)
{
    int n, v, a, ch, code, bsize;
    int coef_nb_bits, total_gain;
    int nb_coefs[MAX_CHANNELS];
    float mdct_norm;

#ifdef TRACE
    tprintf(s->avctx, "***decode_block: %d:%d\n", s->frame_count - 1, s->block_num);
#endif

    /* compute current block length */
    if (s->use_variable_block_len) {
        n = av_log2(s->nb_block_sizes - 1) + 1;

        if (s->reset_block_lengths) {
            s->reset_block_lengths = 0;
            v = get_bits(&s->gb, n);
            if (v >= s->nb_block_sizes)
                return -1;
            s->prev_block_len_bits = s->frame_len_bits - v;
            v = get_bits(&s->gb, n);
            if (v >= s->nb_block_sizes)
                return -1;
            s->block_len_bits = s->frame_len_bits - v;
        } else {
            /* update block lengths */
            s->prev_block_len_bits = s->block_len_bits;
            s->block_len_bits = s->next_block_len_bits;
        }
        v = get_bits(&s->gb, n);
        if (v >= s->nb_block_sizes)
            return -1;
        s->next_block_len_bits = s->frame_len_bits - v;
    } else {
        /* fixed block len */
        s->next_block_len_bits = s->frame_len_bits;
        s->prev_block_len_bits = s->frame_len_bits;
        s->block_len_bits = s->frame_len_bits;
    }

    /* now check if the block length is coherent with the frame length */
    s->block_len = 1 << s->block_len_bits;
    if ((s->block_pos + s->block_len) > s->frame_len)
        return -1;

    if (s->nb_channels == 2) {
        s->ms_stereo = get_bits1(&s->gb);
    }
    v = 0;
    for(ch = 0; ch < s->nb_channels; ch++) {
        a = get_bits1(&s->gb);
        s->channel_coded[ch] = a;
        v |= a;
    }
    /* if no channel coded, no need to go further */
    /* XXX: fix potential framing problems */
    if (!v)
        goto next;

    bsize = s->frame_len_bits - s->block_len_bits;

    /* read total gain and extract corresponding number of bits for
       coef escape coding */
    total_gain = 1;
    for(;;) {
        a = get_bits(&s->gb, 7);
        total_gain += a;
        if (a != 127)
            break;
    }

    coef_nb_bits= ff_wma_total_gain_to_bits(total_gain);

    /* compute number of coefficients */
    n = s->coefs_end[bsize] - s->coefs_start;
    for(ch = 0; ch < s->nb_channels; ch++)
        nb_coefs[ch] = n;

    /* complex coding */
    if (s->use_noise_coding) {

        for(ch = 0; ch < s->nb_channels; ch++) {
            if (s->channel_coded[ch]) {
                int i, n, a;
                n = s->exponent_high_sizes[bsize];
                for(i=0;i<n;i++) {
                    a = get_bits1(&s->gb);
                    s->high_band_coded[ch][i] = a;
                    /* if noise coding, the coefficients are not transmitted */