mpegaudiodec.c

        INT_AA(0)
        INT_AA(1)
        INT_AA(2)
        INT_AA(3)
        INT_AA(4)
        INT_AA(5)
        INT_AA(6)
        INT_AA(7)

        ptr += 18;
    }
}

static void compute_antialias_float(MPADecodeContext *s,
                              GranuleDef *g)
{
    int32_t *ptr;
    int n, i;

    /* we antialias only "long" bands */
    if (g->block_type == 2) {
        if (!g->switch_point)
            return;
        /* XXX: check this for 8000Hz case */
        n = 1;
    } else {
        n = SBLIMIT - 1;
    }

    ptr = g->sb_hybrid + 18;
    for(i = n;i > 0;i--) {
        float tmp0, tmp1;
        float *csa = &csa_table_float[0][0];
#define FLOAT_AA(j)\
        tmp0= ptr[-1-j];\
        tmp1= ptr[   j];\
        ptr[-1-j] = lrintf(tmp0 * csa[0+4*j] - tmp1 * csa[1+4*j]);\
        ptr[   j] = lrintf(tmp0 * csa[1+4*j] + tmp1 * csa[0+4*j]);

        FLOAT_AA(0)
        FLOAT_AA(1)
        FLOAT_AA(2)
        FLOAT_AA(3)
        FLOAT_AA(4)
        FLOAT_AA(5)
        FLOAT_AA(6)
        FLOAT_AA(7)

        ptr += 18;
    }
}

static void compute_imdct(MPADecodeContext *s,
                          GranuleDef *g,
                          int32_t *sb_samples,
                          int32_t *mdct_buf)
{
    int32_t *ptr, *win, *win1, *buf, *out_ptr, *ptr1;
    int32_t out2[12];
    int i, j, mdct_long_end, v, sblimit;

    /* find last non zero block */
    ptr = g->sb_hybrid + 576;
    ptr1 = g->sb_hybrid + 2 * 18;
    while (ptr >= ptr1) {
        ptr -= 6;
        v = ptr[0] | ptr[1] | ptr[2] | ptr[3] | ptr[4] | ptr[5];
        if (v != 0)
            break;
    }
    sblimit = ((ptr - g->sb_hybrid) / 18) + 1;

    if (g->block_type == 2) {
        /* XXX: check for 8000 Hz */
        if (g->switch_point)
            mdct_long_end = 2;
        else
            mdct_long_end = 0;
    } else {
        mdct_long_end = sblimit;
    }

    buf = mdct_buf;
    ptr = g->sb_hybrid;
    for(j=0;j<mdct_long_end;j++) {
        /* apply window & overlap with previous buffer */
        out_ptr = sb_samples + j;
        /* select window */
        if (g->switch_point && j < 2)
            win1 = mdct_win[0];
        else
            win1 = mdct_win[g->block_type];
        /* select frequency inversion */
        win = win1 + ((4 * 36) & -(j & 1));
        imdct36(out_ptr, buf, ptr, win);
        out_ptr += 18*SBLIMIT;
        ptr += 18;
        buf += 18;
    }
    for(j=mdct_long_end;j<sblimit;j++) {
        /* select frequency inversion */
        win = mdct_win[2] + ((4 * 36) & -(j & 1));
        out_ptr = sb_samples + j;

        for(i=0; i<6; i++){
            *out_ptr = buf[i];
            out_ptr += SBLIMIT;
        }
        imdct12(out2, ptr + 0);
        for(i=0;i<6;i++) {
            *out_ptr = MULH(out2[i], win[i]) + buf[i + 6*1];
            buf[i + 6*2] = MULH(out2[i + 6], win[i + 6]);
            out_ptr += SBLIMIT;
        }
        imdct12(out2, ptr + 1);
        for(i=0;i<6;i++) {
            *out_ptr = MULH(out2[i], win[i]) + buf[i + 6*2];
            buf[i + 6*0] = MULH(out2[i + 6], win[i + 6]);
            out_ptr += SBLIMIT;
        }
        imdct12(out2, ptr + 2);
        for(i=0;i<6;i++) {
            buf[i + 6*0] = MULH(out2[i], win[i]) + buf[i + 6*0];
            buf[i + 6*1] = MULH(out2[i + 6], win[i + 6]);
            buf[i + 6*2] = 0;
        }
        ptr += 18;
        buf += 18;
    }
    /* zero bands */
    for(j=sblimit;j<SBLIMIT;j++) {
        /* overlap */
        out_ptr = sb_samples + j;
        for(i=0;i<18;i++) {
            *out_ptr = buf[i];
            buf[i] = 0;
            out_ptr += SBLIMIT;
        }
        buf += 18;
    }
}

#if defined(DEBUG)
void sample_dump(int fnum, int32_t *tab, int n)
{
    static FILE *files[16], *f;
    char buf[512];
    int i;
    int32_t v;

    f = files[fnum];
    if (!f) {
        snprintf(buf, sizeof(buf), "/tmp/out%d.%s.pcm",
                fnum,
#ifdef USE_HIGHPRECISION
                "hp"
#else
                "lp"
#endif
                );
        f = fopen(buf, "w");
        if (!f)
            return;
        files[fnum] = f;
    }

    if (fnum == 0) {
        static int pos = 0;
        av_log(NULL, AV_LOG_DEBUG, "pos=%d\n", pos);
        for(i=0;i<n;i++) {
            av_log(NULL, AV_LOG_DEBUG, " %0.4f", (double)tab[i] / FRAC_ONE);
            if ((i % 18) == 17)
                av_log(NULL, AV_LOG_DEBUG, "\n");
        }
        pos += n;
    }
    for(i=0;i<n;i++) {
        /* normalize to 23 frac bits */
        v = tab[i] << (23 - FRAC_BITS);
        fwrite(&v, 1, sizeof(int32_t), f);
    }
}
#endif


/* main layer3 decoding function */
static int mp_decode_layer3(MPADecodeContext *s)
{
    int nb_granules, main_data_begin, private_bits;
    int gr, ch, blocksplit_flag, i, j, k, n, bits_pos, bits_left;
    GranuleDef granules[2][2], *g;
    int16_t exponents[576];

    /* read side info */
    if (s->lsf) {
        main_data_begin = get_bits(&s->gb, 8);
        private_bits = get_bits(&s->gb, s->nb_channels);
        nb_granules = 1;
    } else {
        main_data_begin = get_bits(&s->gb, 9);
        if (s->nb_channels == 2)
            private_bits = get_bits(&s->gb, 3);
        else
            private_bits = get_bits(&s->gb, 5);
        nb_granules = 2;
        for(ch=0;ch<s->nb_channels;ch++) {
            granules[ch][0].scfsi = 0; /* all scale factors are transmitted */
            granules[ch][1].scfsi = get_bits(&s->gb, 4);
        }
    }

    for(gr=0;gr<nb_granules;gr++) {
        for(ch=0;ch<s->nb_channels;ch++) {
            dprintf("gr=%d ch=%d: side_info\n", gr, ch);
            g = &granules[ch][gr];
            g->part2_3_length = get_bits(&s->gb, 12);
            g->big_values = get_bits(&s->gb, 9);
            g->global_gain = get_bits(&s->gb, 8);
            /* if MS stereo only is selected, we precompute the
               1/sqrt(2) renormalization factor */
            if ((s->mode_ext & (MODE_EXT_MS_STEREO | MODE_EXT_I_STEREO)) ==
                MODE_EXT_MS_STEREO)
                g->global_gain -= 2;
            if (s->lsf)
                g->scalefac_compress = get_bits(&s->gb, 9);
            else
                g->scalefac_compress = get_bits(&s->gb, 4);
            blocksplit_flag = get_bits(&s->gb, 1);
            if (blocksplit_flag) {
                g->block_type = get_bits(&s->gb, 2);
                if (g->block_type == 0)
                    return -1;
                g->switch_point = get_bits(&s->gb, 1);
                for(i=0;i<2;i++)
                    g->table_select[i] = get_bits(&s->gb, 5);
                for(i=0;i<3;i++)
                    g->subblock_gain[i] = get_bits(&s->gb, 3);
                /* compute huffman coded region sizes */
                if (g->block_type == 2)
                    g->region_size[0] = (36 / 2);
                else {
                    if (s->sample_rate_index <= 2)
                        g->region_size[0] = (36 / 2);
                    else if (s->sample_rate_index != 8)
                        g->region_size[0] = (54 / 2);
                    else
                        g->region_size[0] = (108 / 2);
                }
                g->region_size[1] = (576 / 2);
            } else {
                int region_address1, region_address2, l;
                g->block_type = 0;
                g->switch_point = 0;
                for(i=0;i<3;i++)
                    g->table_select[i] = get_bits(&s->gb, 5);
                /* compute huffman coded region sizes */
                region_address1 = get_bits(&s->gb, 4);
                region_address2 = get_bits(&s->gb, 3);
                dprintf("region1=%d region2=%d\n",
                        region_address1, region_address2);
                g->region_size[0] =
                    band_index_long[s->sample_rate_index][region_address1 + 1] >> 1;
                l = region_address1 + region_address2 + 2;
                /* should not overflow */
                if (l > 22)
                    l = 22;
                g->region_size[1] =
                    band_index_long[s->sample_rate_index][l] >> 1;
            }
            /* convert region offsets to region sizes and truncate
               size to big_values */
            g->region_size[2] = (576 / 2);
            j = 0;
            for(i=0;i<3;i++) {
                k = FFMIN(g->region_size[i], g->big_values);
                g->region_size[i] = k - j;
                j = k;
            }

            /* compute band indexes */
            if (g->block_type == 2) {
                if (g->switch_point) {
                    /* if switched mode, we handle the 36 first samples as
                       long blocks.  For 8000Hz, we handle the 48 first
                       exponents as long blocks (XXX: check this!) */
                    if (s->sample_rate_index <= 2)
                        g->long_end = 8;
                    else if (s->sample_rate_index != 8)
                        g->long_end = 6;
                    else
                        g->long_end = 4; /* 8000 Hz */

                    g->short_start = 2 + (s->sample_rate_index != 8);
                } else {
                    g->long_end = 0;
                    g->short_start = 0;
                }
            } else {
                g->short_start = 13;
                g->long_end = 22;
            }

            g->preflag = 0;
            if (!s->lsf)
                g->preflag = get_bits(&s->gb, 1);
            g->scalefac_scale = get_bits(&s->gb, 1);
            g->count1table_select = get_bits(&s->gb, 1);
            dprintf("block_type=%d switch_point=%d\n",
                    g->block_type, g->switch_point);
        }
    }

  if (!s->adu_mode) {
    /* now we get bits from the main_data_begin offset */
    dprintf("seekback: %d\n", main_data_begin);
    seek_to_maindata(s, main_data_begin);
  }

    for(gr=0;gr<nb_granules;gr++) {
        for(ch=0;ch<s->nb_channels;ch++) {
            g = &granules[ch][gr];

            bits_pos = get_bits_count(&s->gb);

            if (!s->lsf) {
                uint8_t *sc;
                int slen, slen1, slen2;

                /* MPEG1 scale factors */
                slen1 = slen_table[0][g->scalefac_compress];
                slen2 = slen_table[1][g->scalefac_compress];
                dprintf("slen1=%d slen2=%d\n", slen1, slen2);
                if (g->block_type == 2) {
                    n = g->switch_point ? 17 : 18;
                    j = 0;
                    if(slen1){
                        for(i=0;i<n;i++)
                            g->scale_factors[j++] = get_bits(&s->gb, slen1);
                    }else{
                        for(i=0;i<n;i++)
                            g->scale_factors[j++] = 0;
                    }
                    if(slen2){
                        for(i=0;i<18;i++)
                            g->scale_factors[j++] = get_bits(&s->gb, slen2);
                        for(i=0;i<3;i++)
                            g->scale_factors[j++] = 0;
                    }else{
                        for(i=0;i<21;i++)
                            g->scale_factors[j++] = 0;
                    }
                } else {
                    sc = granules[ch][0].scale_factors;
                    j = 0;
                    for(k=0;k<4;k++) {
                        n = (k == 0 ? 6 : 5);
                        if ((g->scfsi & (0x8 >> k)) == 0) {
                            slen = (k < 2) ? slen1 : slen2;
                            if(slen){
                                for(i=0;i<n;i++)
                                    g->scale_factors[j++] = get_bits(&s->gb, slen);
                            }else{
                                for(i=0;i<n;i++)
                                    g->scale_factors[j++] = 0;
                            }
                        } else {
                            /* simply copy from last granule */
                            for(i=0;i<n;i++) {
                                g->scale_factors[j] = sc[j];
                                j++;
                            }
                        }
                    }
                    g->scale_factors[j++] = 0;
                }
#if defined(DEBUG)
                {
                    dprintf("scfsi=%x gr=%d ch=%d scale_factors:\n",
                           g->scfsi, gr, ch);
                    for(i=0;i<j;i++)
                        dprintf(" %d", g->scale_factors[i]);
                    dprintf("\n");
                }
#endif
            } else {
                int tindex, tindex2, slen[4], sl, sf;

                /* LSF scale factors */
                if (g->block_type == 2) {
                    tindex = g->switch_point ? 2 : 1;
                } else {
                    tindex = 0;
                }
                sf = g->scalefac_compress;
                if ((s->mode_ext & MODE_EXT_I_STEREO) && ch == 1) {
                    /* intensity stereo case */
                    sf >>= 1;
                    if (sf < 180) {
                        lsf_sf_expand(slen, sf, 6, 6, 0);
                        tindex2 = 3;
                    } else if (sf < 244) {
                        lsf_sf_expand(slen, sf - 180, 4, 4, 0);
                        tindex2 = 4;
                    } else {
                        lsf_sf_expand(slen, sf - 244, 3, 0, 0);
                        tindex2 = 5;
                    }
                } else {
                    /* normal case */
                    if (sf < 400) {
                        lsf_sf_expand(slen, sf, 5, 4, 4);
                        tindex2 = 0;
                    } else if (sf < 500) {
                        lsf_sf_expand(slen, sf - 400, 5, 4, 0);
                        tindex2 = 1;
                    } else {
                        lsf_sf_expand(slen, sf - 500, 3, 0, 0);
                        tindex2 = 2;
                        g->preflag = 1;
                    }
                }

                j = 0;
                for(k=0;k<4;k++) {
                    n = lsf_nsf_table[tindex2][tindex][k];
                    sl = slen[k];
                    if(sl){
                        for(i=0;i<n;i++)
                            g->scale_factors[j++] = get_bits(&s->gb, sl);
                    }else{
                        for(i=0;i<n;i++)
                            g->scale_factors[j++] = 0;
                    }
                }
                /* XXX: should compute exact size */
                for(;j<40;j++)
                    g->scale_factors[j] = 0;
#if defined(DEBUG)
                {
                    dprintf("gr=%d ch=%d scale_factors:\n",
                           gr, ch);
                    for(i=0;i<40;i++)
                        dprintf(" %d", g->scale_factors[i]);
                    dprintf("\n");
                }
#endif
            }

            exponents_from_scale_factors(s, g, exponents);

            /* read Huffman coded residue */
            if (huffman_decode(s, g, exponents,
                               bits_pos + g->part2_3_length) < 0)
                return -1;
#if defined(DEBUG)
            sample_dump(0, g->sb_hybrid, 576);
#endif

            /* skip extension bits */
            bits_left = g->part2_3_length - (get_bits_count(&s->gb) - bits_pos);
            if (bits_left < 0) {
                dprintf("bits_left=%d\n", bits_left);
                return -1;
            }
            while (bits_left >= 16) {
                skip_bits(&s->gb, 16);
                bits_left -= 16;
            }
            if (bits_left > 0)
                skip_bits(&s->gb, bits_left);
        } /* ch */

        if (s->nb_channels == 2)
            compute_stereo(s, &granules[0][gr], &granules[1][gr]);

        for(ch=0;ch<s->nb_channels;ch++) {
            g = &granules[ch][gr];

            reorder_block(s, g);
#if defined(DEBUG)
            sample_dump(0, g->sb_hybrid, 576);
#endif
            s->compute_antialias(s, g);
#if defined(DEBUG)
            sample_dump(1, g->sb_hybrid, 576);
#endif
            compute_imdct(s, g, &s->sb_samples[ch][18 * gr][0], s->mdct_buf[ch]);
#if defined(DEBUG)
            sample_dump(2, &s->sb_samples[ch][18 * gr][0], 576);
#endif
        }
    } /* gr */
    return nb_granules * 18;
}

static int mp_decode_frame(MPADecodeContext *s,
                           OUT_INT *samples)
{
    int i, nb_frames, ch;
    OUT_INT *samples_ptr;

    init_get_bits(&s->gb, s->inbuf + HEADER_SIZE,
                  (s->inbuf_ptr - s->inbuf - HEADER_SIZE)*8);

    /* skip error protection field */
    if (s->error_protection)
        get_bits(&s->gb, 16);

    dprintf("frame %d:\n", s->frame_count);
    switch(s->layer) {
    case 1:
        nb_frames = mp_decode_layer1(s);
        break;
    case 2:
        nb_frames = mp_decode_layer2(s);
        break;
    case 3:
    default:
        nb_frames = mp_decode_layer3(s);
        break;
    }
#if defined(DEBUG)
    for(i=0;i<nb_frames;i++) {
        for(ch=0;ch<s->nb_channels;ch++) {
            int j;
            dprintf("%d-%d:", i, ch);
            for(j=0;j<SBLIMIT;j++)
                dprintf(" %0.6f", (double)s->sb_samples[ch][i][j] / FRAC_ONE);
            dprintf("\n");
        }
    }
#endif
    /* apply the synthesis filter */
    for(ch=0;ch<s->nb_channels;ch++) {
        samples_ptr = samples + ch;
        for(i=0;i<nb_frames;i++) {
            ff_mpa_synth_filter(s->synth_buf[ch], &(s->synth_buf_offset[ch]),
                         window, &s->dither_state,
                         samples_ptr, s->nb_channels,
                         s->sb_samples[ch][i]);
            samples_ptr += 32 * s->nb_channels;
        }
    }
#ifdef DEBUG
    s->frame_count++;
#endif
    return nb_frames * 32 * sizeof(OUT_INT) * s->nb_channels;
}

static int decode_frame(AVCodecContext * avctx,
                        void *data, int *data_size,
                        uint8_t * buf, int buf_size)
{
    MPADecodeContext *s = avctx->priv_data;
    uint32_t header;
    uint8_t *buf_ptr;
    int len, out_size;
    OUT_INT *out_samples = data;

    buf_ptr = buf;
    while (buf_size > 0) {
        len = s->inbuf_ptr - s->inbuf;
        if (s->frame_size == 0) {
            /* special case for next header for first frame in free
               format case (XXX: find a simpler method) */
            if (s->free_format_next_header != 0) {
                s->inbuf[0] = s->free_format_next_header >> 24;
                s->inbuf[1] = s->free_format_next_header >> 16;
                s->inbuf[2] = s->free_format_next_header >> 8;
                s->inbuf[3] = s->free_format_next_header;
                s->inbuf_ptr = s->inbuf + 4;
                s->free_format_next_header = 0;
                goto got_header;
            }
            /* no header seen : find one. We need at least HEADER_SIZE
               bytes to parse it */
            len = HEADER_SIZE - len;
            if (len > buf_size)
                len = buf_size;
            if (len > 0) {
                memcpy(s->inbuf_ptr, buf_ptr, len);
                buf_ptr += len;
                buf_size -= len;
                s->inbuf_ptr += len;
            }
            if ((s->inbuf_ptr - s->inbuf) >= HEADER_SIZE) {
            got_header:
                header = (s->inbuf[0] << 24) | (s->inbuf[1] << 16) |
                    (s->inbuf[2] << 8) | s->inbuf[3];

                if (ff_mpa_check_header(header) < 0) {
                    /* no sync found : move by one byte (inefficient, but simple!) */
                    memmove(s->inbuf, s->inbuf + 1, s->inbuf_ptr - s->inbuf - 1);
                    s->inbuf_ptr--;
                    dprintf("skip %x\n", header);
                    /* reset free format frame size to give a chance
                       to get a new bitrate */
                    s->free_format_frame_size = 0;
                } else {
                    if (decode_header(s, header) == 1) {
                        /* free format: prepare to compute frame size */
                        s->frame_size = -1;
                    }
                    /* update codec info */
                    avctx->sample_rate = s->sample_rate;
                    avctx->channels = s->nb_channels;
                    avctx->bit_rate = s->bit_rate;
                    avctx->sub_id = s->layer;
                    switch(s->layer) {
                    case 1:
                        avctx->frame_size = 384;
                        break;
                    case 2:
                        avctx->frame_size = 1152;
                        break;
                    case 3:
                        if (s->lsf)
                            avctx->frame_size = 576;
                        else
                            avctx->frame_size = 1152;
                        break;
                    }
                }
            }
        } else if (s->frame_size == -1) {
            /* free format : find next sync to compute frame size */
            len = MPA_MAX_CODED_FRAME_SIZE - len;
            if (len > buf_size)
                len = buf_size;
            if (len == 0) {
                /* frame too long: resync */
                s->frame_size = 0;
                memmove(s->inbuf, s->inbuf + 1, s->inbuf_ptr - s->inbuf - 1);
                s->inbuf_ptr--;
            } else {
                uint8_t *p, *pend;
                uint32_t header1;
                int padding;

                memcpy(s->inbuf_ptr, buf_ptr, len);
                /* check for header */
                p = s->inbuf_ptr - 3;
                pend = s->inbuf_ptr + len - 4;
                while (p <= pend) {
                    header = (p[0] << 24) | (p[1] << 16) |
                        (p[2] << 8) | p[3];
                    header1 = (s->inbuf[0] << 24) | (s->inbuf[1] << 16) |
                        (s->inbuf[2] << 8) | s->inbuf[3];
                    /* check with high probability that we have a
                       valid header */
                    if ((header & SAME_HEADER_MASK) ==
                        (header1 & SAME_HEADER_MASK)) {
                        /* header found: update pointers */
                        len = (p + 4) - s->inbuf_ptr;
                        buf_ptr += len;
                        buf_size -= len;
                        s->inbuf_ptr = p;
                        /* compute frame size */
                        s->free_format_next_header = header;
                        s->free_format_frame_size = s->inbuf_ptr - s->inbuf;
                        padding = (header1 >> 9) & 1;
                        if (s->layer == 1)
                            s->free_format_frame_size -= padding * 4;
                        else
                            s->free_format_frame_size -= padding;
                        dprintf("free frame size=%d padding=%d\n",
                                s->free_format_frame_size, padding);
                        decode_header(s, header1);
                        goto next_data;
                    }
                    p++;
                }
                /* not found: simply increase pointers */
                buf_ptr += len;
                s->inbuf_ptr += len;
                buf_size -= len;
            }
        } else if (len < s->frame_size) {
            if (s->frame_size > MPA_MAX_CODED_FRAME_SIZE)
                s->frame_size = MPA_MAX_CODED_FRAME_SIZE;
            len = s->frame_size - len;
            if (len > buf_size)
                len = buf_size;
            memcpy(s->inbuf_ptr, buf_ptr, len);
            buf_ptr += len;
            s->inbuf_ptr += len;
            buf_size -= len;
        }
    next_data:
        if (s->frame_size > 0 &&
            (s->inbuf_ptr - s->inbuf) >= s->frame_size) {
            if (avctx->parse_only) {
                /* simply return the frame data */
                *(uint8_t **)data = s->inbuf;
                out_size = s->inbuf_ptr - s->inbuf;
            } else {
                out_size = mp_decode_frame(s, out_samples);
            }
            s->inbuf_ptr = s->inbuf;
            s->frame_size = 0;
            if(out_size>=0)
                *data_size = out_size;
            else
                av_log(avctx, AV_LOG_DEBUG, "Error while decoding mpeg audio frame\n"); //FIXME return -1 / but also return the number of bytes consumed
            break;
        }
    }
    return buf_ptr - buf;
}


static int decode_frame_adu(AVCodecContext * avctx,
                        void *data, int *data_size,
                        uint8_t * buf, int buf_size)
{
    MPADecodeContext *s = avctx->priv_data;
    uint32_t header;
    int len, out_size;
    OUT_INT *out_samples = data;

    len = buf_size;

    // Discard too short frames
    if (buf_size < HEADER_SIZE) {
        *data_size = 0;
        return buf_size;
    }


    if (len > MPA_MAX_CODED_FRAME_SIZE)
        len = MPA_MAX_CODED_FRAME_SIZE;

    memcpy(s->inbuf, buf, len);
    s->inbuf_ptr = s->inbuf + len;

    // Get header and restore sync word
    header = (s->inbuf[0] << 24) | (s->inbuf[1] << 16) |
              (s->inbuf[2] << 8) | s->inbuf[3] | 0xffe00000;

    if (ff_mpa_check_header(header) < 0) { // Bad header, discard frame
        *data_size = 0;
        return buf_size;
    }

    decode_header(s, header);
    /* update codec info */
    avctx->sample_rate = s->sample_rate;
    avctx->channels = s->nb_channels;
    avctx->bit_rate = s->bit_rate;
    avctx->sub_id = s->layer;

    avctx->frame_size=s->frame_size = len;

    if (avctx->parse_only) {
        /* simply return the frame data */
        *(uint8_t **)data = s->inbuf;
        out_size = s->inbuf_ptr - s->inbuf;
    } else {
        out_size = mp_decode_frame(s, out_samples);
    }

    *data_size = out_size;
    return buf_size;
}


/* Next 3 arrays are indexed by channel config number (passed via codecdata) */
static int mp3Frames[16] = {0,1,1,2,3,3,4,5,2};   /* number of mp3 decoder instances */
static int mp3Channels[16] = {0,1,2,3,4,5,6,8,4}; /* total output channels */
/* offsets into output buffer, assume output order is FL FR BL BR C LFE */
static int chan_offset[9][5] = {
    {0},
    {0},            // C
    {0},            // FLR
    {2,0},          // C FLR
    {2,0,3},        // C FLR BS
    {4,0,2},        // C FLR BLRS
    {4,0,2,5},      // C FLR BLRS LFE
    {4,0,2,6,5},    // C FLR BLRS BLR LFE
    {0,2}           // FLR BLRS
};


static int decode_init_mp3on4(AVCodecContext * avctx)
{
    MP3On4DecodeContext *s = avctx->priv_data;
    int i;

    if ((avctx->extradata_size < 2) || (avctx->extradata == NULL)) {
        av_log(avctx, AV_LOG_ERROR, "Codec extradata missing or too short.\n");
        return -1;
    }

    s->chan_cfg = (((unsigned char *)avctx->extradata)[1] >> 3) & 0x0f;
    s->frames = mp3Frames[s->chan_cfg];
    if(!s->frames) {
        av_log(avctx, AV_LOG_ERROR, "Invalid channel config number.\n");
        return -1;
    }
    avctx->channels = mp3Channels[s->chan_cfg];

    /* Init the first mp3 decoder in standard way, so that all tables get builded
     * We replace avctx->priv_data with the context of the first decoder so that
     * decode_init() does not have to be changed.
     * Other decoders will be inited here copying data from the first context
     */
    // Allocate zeroed memory for the first decoder context
    s->mp3decctx[0] = av_mallocz(sizeof(MPADecodeContext));
    // Put decoder context in place to make init_decode() happy
    avctx->priv_data = s->mp3decctx[0];
    decode_init(avctx);
    // Restore mp3on4 context pointer
    avctx->priv_data = s;
    s->mp3decctx[0]->adu_mode = 1; // Set adu mode

    /* Create a separate codec/context for each frame (first is already ok).
     * Each frame is 1 or 2 channels - up to 5 frames allowed
     */
    for (i = 1; i < s->frames; i++) {
        s->mp3decctx[i] = av_mallocz(sizeof(MPADecodeContext));
        s->mp3decctx[i]->compute_antialias = s->mp3decctx[0]->compute_antialias;
        s->mp3decctx[i]->inbuf = &s->mp3decctx[i]->inbuf1[0][BACKSTEP_SIZE];
        s->mp3decctx[i]->inbuf_ptr = s->mp3decctx[i]->inbuf;
        s->mp3decctx[i]->adu_mode = 1;
    }

    return 0;
}


static int decode_close_mp3on4(AVCodecContext * avctx)
{
    MP3On4DecodeContext *s = avctx->priv_data;
    int i;

    for (i = 0; i < s->frames; i++)
        if (s->mp3decctx[i])
            av_free(s->mp3decctx[i]);

    return 0;
}


static int decode_frame_mp3on4(AVCodecContext * avctx,
                        void *data, int *data_size,
                        uint8_t * buf, int buf_size)
{
    MP3On4DecodeContext *s = avctx->priv_data;
    MPADecodeContext *m;
    int len, out_size = 0;
    uint32_t header;
    OUT_INT *out_samples = data;
    OUT_INT decoded_buf[MPA_FRAME_SIZE * MPA_MAX_CHANNELS];
    OUT_INT *outptr, *bp;
    int fsize;
    unsigned char *start2 = buf, *start;
    int fr, i, j, n;
    int off = avctx->channels;
    int *coff = chan_offset[s->chan_cfg];

    len = buf_size;

    // Discard too short frames
    if (buf_size < HEADER_SIZE) {
        *data_size = 0;
        return buf_size;
    }

    // If only one decoder interleave is not needed
    outptr = s->frames == 1 ? out_samples : decoded_buf;

    for (fr = 0; fr < s->frames; fr++) {
        start = start2;
        fsize = (start[0] << 4) | (start[1] >> 4);
        start2 += fsize;
        if (fsize > len)
            fsize = len;
        len -= fsize;
        if (fsize > MPA_MAX_CODED_FRAME_SIZE)
            fsize = MPA_MAX_CODED_FRAME_SIZE;
        m = s->mp3decctx[fr];
        assert (m != NULL);
        /* copy original to new */
        m->inbuf_ptr = m->inbuf + fsize;
        memcpy(m->inbuf, start, fsize);

        // Get header
        header = (m->inbuf[0] << 24) | (m->inbuf[1] << 16) |
                  (m->inbuf[2] << 8) | m->inbuf[3] | 0xfff00000;

        if (ff_mpa_check_header(header) < 0) { // Bad header, discard block
            *data_size = 0;
            return buf_size;
        }

        decode_header(m, header);
        mp_decode_frame(m, decoded_buf);

        n = MPA_FRAME_SIZE * m->nb_channels;
        out_size += n * sizeof(OUT_INT);
        if(s->frames > 1) {
            /* interleave output data */
            bp = out_samples + coff[fr];
            if(m->nb_channels == 1) {
                for(j = 0; j < n; j++) {
                    *bp = decoded_buf[j];
                    bp += off;
                }
            } else {
                for(j = 0; j < n; j++) {
                    bp[0] = decoded_buf[j++];
                    bp[1] = decoded_buf[j];
                    bp += off;
                }
            }
        }
    }

    /* update codec info */
    avctx->sample_rate = s->mp3decctx[0]->sample_rate;
    avctx->frame_size= buf_size;
    avctx->bit_rate = 0;
    for (i = 0; i < s->frames; i++)
        avctx->bit_rate += s->mp3decctx[i]->bit_rate;

    *data_size = out_size;
    return buf_size;
}


AVCodec mp2_decoder =
{
    "mp2",
    CODEC_TYPE_AUDIO,
    CODEC_ID_MP2,
    sizeof(MPADecodeContext),
    decode_init,
    NULL,
    NULL,
    decode_frame,
    CODEC_CAP_PARSE_ONLY,
};

AVCodec mp3_decoder =
{
    "mp3",
    CODEC_TYPE_AUDIO,
    CODEC_ID_MP3,
    sizeof(MPADecodeContext),
    decode_init,
    NULL,
    NULL,
    decode_frame,
    CODEC_CAP_PARSE_ONLY,
};

AVCodec mp3adu_decoder =
{
    "mp3adu",
    CODEC_TYPE_AUDIO,
    CODEC_ID_MP3ADU,
    sizeof(MPADecodeContext),
    decode_init,
    NULL,
    NULL,
    decode_frame_adu,
    CODEC_CAP_PARSE_ONLY,
};

AVCodec mp3on4_decoder =
{
    "mp3on4",
    CODEC_TYPE_AUDIO,
    CODEC_ID_MP3ON4,
    sizeof(MP3On4DecodeContext),
    decode_init_mp3on4,
    NULL,
    decode_close_mp3on4,
    decode_frame_mp3on4,
    0
};