ac3enc.c

从FFMPEG转换而来的H264解码程序,VC下编译..

        case EXP_REUSE:
            continue;
        case EXP_D15:
            group_size = 1;
            break;
        case EXP_D25:
            group_size = 2;
            break;
        default:
        case EXP_D45:
            group_size = 4;
            break;
        }
        nb_groups = (s->nb_coefs[ch] + (group_size * 3) - 4) / (3 * group_size);
        p = encoded_exp[ch];

        /* first exponent */
        exp1 = *p++;
        put_bits(&s->pb, 4, exp1);

        /* next ones are delta encoded */
        for(i=0;i<nb_groups;i++) {
            /* merge three delta in one code */
            exp0 = exp1;
            exp1 = p[0];
            p += group_size;
            delta0 = exp1 - exp0 + 2;

            exp0 = exp1;
            exp1 = p[0];
            p += group_size;
            delta1 = exp1 - exp0 + 2;

            exp0 = exp1;
            exp1 = p[0];
            p += group_size;
            delta2 = exp1 - exp0 + 2;

            put_bits(&s->pb, 7, ((delta0 * 5 + delta1) * 5) + delta2);
        }

        if (ch != s->lfe_channel)
            put_bits(&s->pb, 2, 0); /* no gain range info */
    }

    /* bit allocation info */
    baie = (block_num == 0);
    put_bits(&s->pb, 1, baie);
    if (baie) {
        put_bits(&s->pb, 2, s->sdecaycod);
        put_bits(&s->pb, 2, s->fdecaycod);
        put_bits(&s->pb, 2, s->sgaincod);
        put_bits(&s->pb, 2, s->dbkneecod);
        put_bits(&s->pb, 3, s->floorcod);
    }

    /* snr offset */
    put_bits(&s->pb, 1, baie); /* always present with bai */
    if (baie) {
        put_bits(&s->pb, 6, s->csnroffst);
        for(ch=0;ch<s->nb_all_channels;ch++) {
            put_bits(&s->pb, 4, s->fsnroffst[ch]);
            put_bits(&s->pb, 3, s->fgaincod[ch]);
        }
    }

    put_bits(&s->pb, 1, 0); /* no delta bit allocation */
    put_bits(&s->pb, 1, 0); /* no data to skip */

    /* mantissa encoding : we use two passes to handle the grouping. A
       one pass method may be faster, but it would necessitate to
       modify the output stream. */

    /* first pass: quantize */
    mant1_cnt = mant2_cnt = mant4_cnt = 0;
    qmant1_ptr = qmant2_ptr = qmant4_ptr = NULL;

    for (ch = 0; ch < s->nb_all_channels; ch++) {
        int b, c, e, v;

        for(i=0;i<s->nb_coefs[ch];i++) {
            c = mdct_coefs[ch][i];
            e = encoded_exp[ch][i] - global_exp[ch];
            b = bap[ch][i];
            switch(b) {
            case 0:
                v = 0;
                break;
            case 1:
                v = sym_quant(c, e, 3);
                switch(mant1_cnt) {
                case 0:
                    qmant1_ptr = &qmant[ch][i];
                    v = 9 * v;
                    mant1_cnt = 1;
                    break;
                case 1:
                    *qmant1_ptr += 3 * v;
                    mant1_cnt = 2;
                    v = 128;
                    break;
                default:
                    *qmant1_ptr += v;
                    mant1_cnt = 0;
                    v = 128;
                    break;
                }
                break;
            case 2:
                v = sym_quant(c, e, 5);
                switch(mant2_cnt) {
                case 0:
                    qmant2_ptr = &qmant[ch][i];
                    v = 25 * v;
                    mant2_cnt = 1;
                    break;
                case 1:
                    *qmant2_ptr += 5 * v;
                    mant2_cnt = 2;
                    v = 128;
                    break;
                default:
                    *qmant2_ptr += v;
                    mant2_cnt = 0;
                    v = 128;
                    break;
                }
                break;
            case 3:
                v = sym_quant(c, e, 7);
                break;
            case 4:
                v = sym_quant(c, e, 11);
                switch(mant4_cnt) {
                case 0:
                    qmant4_ptr = &qmant[ch][i];
                    v = 11 * v;
                    mant4_cnt = 1;
                    break;
                default:
                    *qmant4_ptr += v;
                    mant4_cnt = 0;
                    v = 128;
                    break;
                }
                break;
            case 5:
                v = sym_quant(c, e, 15);
                break;
            case 14:
                v = asym_quant(c, e, 14);
                break;
            case 15:
                v = asym_quant(c, e, 16);
                break;
            default:
                v = asym_quant(c, e, b - 1);
                break;
            }
            qmant[ch][i] = v;
        }
    }

    /* second pass : output the values */
    for (ch = 0; ch < s->nb_all_channels; ch++) {
        int b, q;

        for(i=0;i<s->nb_coefs[ch];i++) {
            q = qmant[ch][i];
            b = bap[ch][i];
            switch(b) {
            case 0:
                break;
            case 1:
                if (q != 128)
                    put_bits(&s->pb, 5, q);
                break;
            case 2:
                if (q != 128)
                    put_bits(&s->pb, 7, q);
                break;
            case 3:
                put_bits(&s->pb, 3, q);
                break;
            case 4:
                if (q != 128)
                    put_bits(&s->pb, 7, q);
                break;
            case 14:
                put_bits(&s->pb, 14, q);
                break;
            case 15:
                put_bits(&s->pb, 16, q);
                break;
            default:
                put_bits(&s->pb, b - 1, q);
                break;
            }
        }
    }
}

#define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))

static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)
{
    unsigned int c;

    c = 0;
    while (a) {
        if (a & 1)
            c ^= b;
        a = a >> 1;
        b = b << 1;
        if (b & (1 << 16))
            b ^= poly;
    }
    return c;
}

static unsigned int pow_poly(unsigned int a, unsigned int n, unsigned int poly)
{
    unsigned int r;
    r = 1;
    while (n) {
        if (n & 1)
            r = mul_poly(r, a, poly);
        a = mul_poly(a, a, poly);
        n >>= 1;
    }
    return r;
}


/* compute log2(max(abs(tab[]))) */
static int log2_tab(int16_t *tab, int n)
{
    int i, v;

    v = 0;
    for(i=0;i<n;i++) {
        v |= abs(tab[i]);
    }
    return av_log2(v);
}

static void lshift_tab(int16_t *tab, int n, int lshift)
{
    int i;

    if (lshift > 0) {
        for(i=0;i<n;i++) {
            tab[i] <<= lshift;
        }
    } else if (lshift < 0) {
        lshift = -lshift;
        for(i=0;i<n;i++) {
            tab[i] >>= lshift;
        }
    }
}

/* fill the end of the frame and compute the two crcs */
static int output_frame_end(AC3EncodeContext *s)
{
    int frame_size, frame_size_58, n, crc1, crc2, crc_inv;
    uint8_t *frame;

    frame_size = s->frame_size; /* frame size in words */
    /* align to 8 bits */
    flush_put_bits(&s->pb);
    /* add zero bytes to reach the frame size */
    frame = s->pb.buf;
    n = 2 * s->frame_size - (pbBufPtr(&s->pb) - frame) - 2;
    //assert(n >= 0);
    if(n>0)
      memset(pbBufPtr(&s->pb), 0, n);

    /* Now we must compute both crcs : this is not so easy for crc1
       because it is at the beginning of the data... */
    frame_size_58 = (frame_size >> 1) + (frame_size >> 3);
    crc1 = bswap_16(av_crc(av_crc8005, 0, frame + 4, 2 * frame_size_58 - 4));
    /* XXX: could precompute crc_inv */
    crc_inv = pow_poly((CRC16_POLY >> 1), (16 * frame_size_58) - 16, CRC16_POLY);
    crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);
    AV_WB16(frame+2,crc1);

    crc2 = bswap_16(av_crc(av_crc8005, 0, frame + 2 * frame_size_58, (frame_size - frame_size_58) * 2 - 2));
    AV_WB16(frame+2*frame_size-2,crc2);

    //    printf("n=%d frame_size=%d\n", n, frame_size);
    return frame_size * 2;
}

static int AC3_encode_frame(AVCodecContext *avctx,
                            unsigned char *frame, int buf_size, void *data)
{
    AC3EncodeContext *s = avctx->priv_data;
    int16_t *samples = data;
    int i, j, k, v, ch;
    int16_t input_samples[N];
    int32_t mdct_coef[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
    uint8_t exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
    uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS];
    uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
    uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
    int8_t exp_samples[NB_BLOCKS][AC3_MAX_CHANNELS];
    int frame_bits;

    frame_bits = 0;
    for(ch=0;ch<s->nb_all_channels;ch++) {
        /* fixed mdct to the six sub blocks & exponent computation */
        for(i=0;i<NB_BLOCKS;i++) {
            int16_t *sptr;
            int sinc;

            /* compute input samples */
            memcpy(input_samples, s->last_samples[ch], N/2 * sizeof(int16_t));
            sinc = s->nb_all_channels;
            sptr = samples + (sinc * (N/2) * i) + avctx->ac3channels[ch]; /* intentional diff from ffmpeg */
            for(j=0;j<N/2;j++) {
                v = *sptr;
                input_samples[j + N/2] = v;
                s->last_samples[ch][j] = v;
                sptr += sinc;
            }

            /* apply the MDCT window */
            for(j=0;j<N/2;j++) {
                input_samples[j] = MUL16(input_samples[j],
                                         ff_ac3_window[j]) >> 15;
                input_samples[N-j-1] = MUL16(input_samples[N-j-1],
                                             ff_ac3_window[j]) >> 15;
            }

            /* Normalize the samples to use the maximum available
               precision */
            v = 14 - log2_tab(input_samples, N);
            if (v < 0)
                v = 0;
            exp_samples[i][ch] = v - 8; /* intentional diff from ffmpeg */
            lshift_tab(input_samples, N, v);

            /* do the MDCT */
            mdct512(mdct_coef[i][ch], input_samples);

            /* compute "exponents". We take into account the
               normalization there */
            for(j=0;j<N/2;j++) {
                int e;
                v = abs(mdct_coef[i][ch][j]);
                if (v == 0)
                    e = 24;
                else {
                    e = 23 - av_log2(v) + exp_samples[i][ch];
                    if (e >= 24) {
                        e = 24;
                        mdct_coef[i][ch][j] = 0;
                    }
                }
                exp[i][ch][j] = e;
            }
        }

        compute_exp_strategy(exp_strategy, exp, ch, ch == s->lfe_channel);

        /* compute the exponents as the decoder will see them. The
           EXP_REUSE case must be handled carefully : we select the
           min of the exponents */
        i = 0;
        while (i < NB_BLOCKS) {
            j = i + 1;
            while (j < NB_BLOCKS && exp_strategy[j][ch] == EXP_REUSE) {
                exponent_min(exp[i][ch], exp[j][ch], s->nb_coefs[ch]);
                j++;
            }
            frame_bits += encode_exp(encoded_exp[i][ch],
                                     exp[i][ch], s->nb_coefs[ch],
                                     exp_strategy[i][ch]);
            /* copy encoded exponents for reuse case */
            for(k=i+1;k<j;k++) {
                memcpy(encoded_exp[k][ch], encoded_exp[i][ch],
                       s->nb_coefs[ch] * sizeof(uint8_t));
            }
            i = j;
        }
    }

    /* adjust for fractional frame sizes */
    while(s->bits_written >= s->bit_rate*1000 && s->samples_written >= s->sample_rate) {
        s->bits_written -= s->bit_rate*1000;
        s->samples_written -= s->sample_rate;
    }
    s->frame_size = s->frame_size_min + (s->bits_written * s->sample_rate < s->samples_written * s->bit_rate*1000);
    s->bits_written += s->frame_size * 16;
    s->samples_written += AC3_FRAME_SIZE;

    compute_bit_allocation(s, bap, encoded_exp, exp_strategy, frame_bits);
    /* everything is known... let's output the frame */
    output_frame_header(s, frame);

    for(i=0;i<NB_BLOCKS;i++) {
        output_audio_block(s, exp_strategy[i], encoded_exp[i],
                           bap[i], mdct_coef[i], exp_samples[i], i);
    }
    return output_frame_end(s);
}

static int AC3_encode_close(AVCodecContext *avctx)
{
    av_freep(&avctx->coded_frame);
    return 0;
}

AVCodec ac3_encoder = {
    "ac3",
    CODEC_TYPE_AUDIO,
    CODEC_ID_AC3,
    sizeof(AC3EncodeContext),
    /*.init=*/AC3_encode_init,
    /*.encode=*/AC3_encode_frame,
    /*.close=*/AC3_encode_close,
    /*.decode=*/NULL,
};