syntax.c

aac解码器源程序在Visual C++下的实现

    /* Stereo2 / Mono1 */
    ics1->tns_data_present = faad_get1bit(ld);

#if defined(LTP_DEC)
    ics1->ltp.data_present = faad_get1bit(ld);
#elif defined (DRM)
    if(faad_get1bit(ld)) {
         hInfo->error = 26;
         return;
    }
#else
    faad_get1bit(ld);
#endif    

    hInfo->error = side_info(hDecoder, &cpe, ld, ics1, 1);
    if (hInfo->error > 0)
        return;
    if (this_layer_stereo)
    {
        /* Stereo3 */
        ics2->tns_data_present = faad_get1bit(ld);
#ifdef LTP_DEC
        ics1->ltp.data_present =
#endif
            faad_get1bit(ld);
        hInfo->error = side_info(hDecoder, &cpe, ld, ics2, 1);
        if (hInfo->error > 0)
            return;
    }
    /* Stereo4 / Mono2 */
    if (ics1->tns_data_present)
        tns_data(ics1, &(ics1->tns), ld);
    if (this_layer_stereo)
    {
        /* Stereo5 */
        if (ics2->tns_data_present)
            tns_data(ics2, &(ics2->tns), ld);
    }

#ifdef DRM
    /* CRC check */
    if (hDecoder->object_type == DRM_ER_LC)
    {
        if ((hInfo->error = (uint8_t)faad_check_CRC(ld, (uint16_t)faad_get_processed_bits(ld) - 8)) > 0)
            return;
    }
#endif

    /* Stereo6 / Mono3 */
    /* error resilient spectral data decoding */
    if ((hInfo->error = reordered_spectral_data(hDecoder, ics1, ld, spec_data1)) > 0)
    {
        return;
    }
    if (this_layer_stereo)
    {
        /* Stereo7 */
        /* error resilient spectral data decoding */
        if ((hInfo->error = reordered_spectral_data(hDecoder, ics2, ld, spec_data2)) > 0)
        {
            return;
        }
    }


#ifdef DRM
#ifdef SBR_DEC
    /* In case of DRM we need to read the SBR info before channel reconstruction */
    if ((hDecoder->sbr_present_flag == 1) && (hDecoder->object_type == DRM_ER_LC))
    {
        bitfile ld_sbr = {0};
        uint32_t i;
        uint16_t count = 0;
        uint8_t *revbuffer;
        uint8_t *prevbufstart;
        uint8_t *pbufend;

        /* all forward bitreading should be finished at this point */
        uint32_t bitsconsumed = faad_get_processed_bits(ld);
        uint32_t buffer_size = faad_origbitbuffer_size(ld);
        uint8_t *buffer = (uint8_t*)faad_origbitbuffer(ld);

        if (bitsconsumed + 8 > buffer_size*8)
        {
            hInfo->error = 14;
            return;
        }

        if (!hDecoder->sbr[0])
        {
            hDecoder->sbr[0] = sbrDecodeInit(hDecoder->frameLength, hDecoder->element_id[0],
                2*get_sample_rate(hDecoder->sf_index), 0 /* ds SBR */, 1);
        }

        /* Reverse bit reading of SBR data in DRM audio frame */
        revbuffer = (uint8_t*)faad_malloc(buffer_size*sizeof(uint8_t));
        prevbufstart = revbuffer;
        pbufend = &buffer[buffer_size - 1];
        for (i = 0; i < buffer_size; i++)
            *prevbufstart++ = tabFlipbits[*pbufend--];

        /* Set SBR data */
        /* consider 8 bits from AAC-CRC */
        /* SBR buffer size is original buffer size minus AAC buffer size */
        count = (uint16_t)bit2byte(buffer_size*8 - bitsconsumed);
        faad_initbits(&ld_sbr, revbuffer, count);

        hDecoder->sbr[0]->sample_rate = get_sample_rate(hDecoder->sf_index);
        hDecoder->sbr[0]->sample_rate *= 2;

        faad_getbits(&ld_sbr, 8); /* Skip 8-bit CRC */

        hDecoder->sbr[0]->ret = sbr_extension_data(&ld_sbr, hDecoder->sbr[0], count, hDecoder->postSeekResetFlag);
#if (defined(PS_DEC) || defined(DRM_PS))
        if (hDecoder->sbr[0]->ps_used)
        {
            hDecoder->ps_used[0] = 1;
            hDecoder->ps_used_global = 1;
        }
#endif

        if (ld_sbr.error)
        {
            hDecoder->sbr[0]->ret = 1;
        }

        /* check CRC */
        /* no need to check it if there was already an error */
        if (hDecoder->sbr[0]->ret == 0)
            hDecoder->sbr[0]->ret = (uint8_t)faad_check_CRC(&ld_sbr, (uint16_t)faad_get_processed_bits(&ld_sbr) - 8);

        /* SBR data was corrupted, disable it until the next header */
        if (hDecoder->sbr[0]->ret != 0)
        {
            hDecoder->sbr[0]->header_count = 0;
        }

        faad_endbits(&ld_sbr);

        if (revbuffer)
            faad_free(revbuffer);
    }
#endif
#endif

    if (this_layer_stereo)
    {
        hInfo->error = reconstruct_channel_pair(hDecoder, ics1, ics2, &cpe, spec_data1, spec_data2);
        if (hInfo->error > 0)
            return;
    } else {
        hInfo->error = reconstruct_single_channel(hDecoder, ics1, &cpe, spec_data1);
        if (hInfo->error > 0)
            return;
    }

    /* map output channels position to internal data channels */
    if (hDecoder->element_output_channels[hDecoder->fr_ch_ele] == 2)
    {
        /* this might be faulty when pce_set is true */
        hDecoder->internal_channel[channels] = channels;
        hDecoder->internal_channel[channels+1] = channels+1;
    } else {
        hDecoder->internal_channel[channels] = channels;
    }

    hDecoder->fr_channels += hDecoder->element_output_channels[hDecoder->fr_ch_ele];
    hDecoder->fr_ch_ele++;

    return;
}

/* Table 4.4.15 */
static int8_t DRM_aac_scalable_main_header(NeAACDecHandle hDecoder, ic_stream *ics1, ic_stream *ics2,
                                           bitfile *ld, uint8_t this_layer_stereo)
{
    uint8_t retval = 0;
    uint8_t ch;
    ic_stream *ics;
    uint8_t ics_reserved_bit;

    ics_reserved_bit = faad_get1bit(ld
        DEBUGVAR(1,300,"aac_scalable_main_header(): ics_reserved_bits"));
    if (ics_reserved_bit != 0)
        return 32;
    ics1->window_sequence = (uint8_t)faad_getbits(ld, 2
        DEBUGVAR(1,301,"aac_scalable_main_header(): window_sequence"));
    ics1->window_shape = faad_get1bit(ld
        DEBUGVAR(1,302,"aac_scalable_main_header(): window_shape"));

    if (ics1->window_sequence == EIGHT_SHORT_SEQUENCE)
    {
        ics1->max_sfb = (uint8_t)faad_getbits(ld, 4
            DEBUGVAR(1,303,"aac_scalable_main_header(): max_sfb (short)"));
        ics1->scale_factor_grouping = (uint8_t)faad_getbits(ld, 7
            DEBUGVAR(1,304,"aac_scalable_main_header(): scale_factor_grouping"));
    } else {
        ics1->max_sfb = (uint8_t)faad_getbits(ld, 6
            DEBUGVAR(1,305,"aac_scalable_main_header(): max_sfb (long)"));
    }

    /* get the grouping information */
    if ((retval = window_grouping_info(hDecoder, ics1)) > 0)
        return retval;

    /* should be an error */
    /* check the range of max_sfb */
    if (ics1->max_sfb > ics1->num_swb)
        return 16;

    if (this_layer_stereo)
    {
        ics1->ms_mask_present = (uint8_t)faad_getbits(ld, 2
            DEBUGVAR(1,306,"aac_scalable_main_header(): ms_mask_present"));
        if (ics1->ms_mask_present == 3)
        {
            /* bitstream error */
            return 32;
        }
        if (ics1->ms_mask_present == 1)
        {
            uint8_t g, sfb;
            for (g = 0; g < ics1->num_window_groups; g++)
            {
                for (sfb = 0; sfb < ics1->max_sfb; sfb++)
                {
                    ics1->ms_used[g][sfb] = faad_get1bit(ld
                        DEBUGVAR(1,307,"aac_scalable_main_header(): faad_get1bit"));
                }
            }
        }

        memcpy(ics2, ics1, sizeof(ic_stream));
    } else {
        ics1->ms_mask_present = 0;
    }

    return 0;
}
#endif

static uint8_t side_info(NeAACDecHandle hDecoder, element *ele,
                         bitfile *ld, ic_stream *ics, uint8_t scal_flag)
{
    uint8_t result;

    ics->global_gain = (uint8_t)faad_getbits(ld, 8
        DEBUGVAR(1,67,"individual_channel_stream(): global_gain"));

    if (!ele->common_window && !scal_flag)
    {
        if ((result = ics_info(hDecoder, ics, ld, ele->common_window)) > 0)
            return result;
    }

    if ((result = section_data(hDecoder, ics, ld)) > 0)
        return result;

    if ((result = scale_factor_data(hDecoder, ics, ld)) > 0)
        return result;

    if (!scal_flag)
    {
        /**
         **  NOTE: It could be that pulse data is available in scalable AAC too,
         **        as said in Amendment 1, this could be only the case for ER AAC,
         **        though. (have to check this out later)
         **/
        /* get pulse data */
        if ((ics->pulse_data_present = faad_get1bit(ld
            DEBUGVAR(1,68,"individual_channel_stream(): pulse_data_present"))) & 1)
        {
            if ((result = pulse_data(ics, &(ics->pul), ld)) > 0)
                return result;
        }

        /* get tns data */
        if ((ics->tns_data_present = faad_get1bit(ld
            DEBUGVAR(1,69,"individual_channel_stream(): tns_data_present"))) & 1)
        {
#ifdef ERROR_RESILIENCE
            if (hDecoder->object_type < ER_OBJECT_START)
#endif
                tns_data(ics, &(ics->tns), ld);
        }

        /* get gain control data */
        if ((ics->gain_control_data_present = faad_get1bit(ld
            DEBUGVAR(1,70,"individual_channel_stream(): gain_control_data_present"))) & 1)
        {
#ifdef SSR_DEC
            if (hDecoder->object_type != SSR)
                return 1;
            else
                gain_control_data(ld, ics);
#else
            return 1;
#endif
        }
    }

#ifdef ERROR_RESILIENCE
    if (hDecoder->aacSpectralDataResilienceFlag)
    {
        ics->length_of_reordered_spectral_data = (uint16_t)faad_getbits(ld, 14
            DEBUGVAR(1,147,"individual_channel_stream(): length_of_reordered_spectral_data"));

        if (hDecoder->channelConfiguration == 2)
        {
            if (ics->length_of_reordered_spectral_data > 6144)
                ics->length_of_reordered_spectral_data = 6144;
        } else {
            if (ics->length_of_reordered_spectral_data > 12288)
                ics->length_of_reordered_spectral_data = 12288;
        }

        ics->length_of_longest_codeword = (uint8_t)faad_getbits(ld, 6
            DEBUGVAR(1,148,"individual_channel_stream(): length_of_longest_codeword"));
        if (ics->length_of_longest_codeword >= 49)
            ics->length_of_longest_codeword = 49;
    }

    /* RVLC spectral data is put here */
    if (hDecoder->aacScalefactorDataResilienceFlag)
    {
        if ((result = rvlc_decode_scale_factors(ics, ld)) > 0)
            return result;
    }
#endif

    return 0;
}

/* Table 4.4.24 */
static uint8_t individual_channel_stream(NeAACDecHandle hDecoder, element *ele,
                                         bitfile *ld, ic_stream *ics, uint8_t scal_flag,
                                         int16_t *spec_data)
{
    uint8_t result;

    result = side_info(hDecoder, ele, ld, ics, scal_flag);
    if (result > 0)
        return result;

    if (hDecoder->object_type >= ER_OBJECT_START) 
    {
        if (ics->tns_data_present)
            tns_data(ics, &(ics->tns), ld);
    }

#ifdef DRM
    /* CRC check */
    if (hDecoder->object_type == DRM_ER_LC)
    {
        if ((result = (uint8_t)faad_check_CRC(ld, (uint16_t)faad_get_processed_bits(ld) - 8)) > 0)
            return result;
    }
#endif

#ifdef ERROR_RESILIENCE
    if (hDecoder->aacSpectralDataResilienceFlag)
    {
        /* error resilient spectral data decoding */
        if ((result = reordered_spectral_data(hDecoder, ics, ld, spec_data)) > 0)
        {
            return result;
        }
    } else {
#endif
        /* decode the spectral data */
        if ((result = spectral_data(hDecoder, ics, ld, spec_data)) > 0)
        {
            return result;
        }
#ifdef ERROR_RESILIENCE
    }
#endif

    /* pulse coding reconstruction */
    if (ics->pulse_data_present)
    {
        if (ics->window_sequence != EIGHT_SHORT_SEQUENCE)
        {
            if ((result = pulse_decode(ics, spec_data, hDecoder->frameLength)) > 0)
                return result;
        } else {
            return 2; /* pulse coding not allowed for short blocks */
        }
    }

    return 0;
}

/* Table 4.4.25 */
static uint8_t section_data(NeAACDecHandle hDecoder, ic_stream *ics, bitfile *ld)
{
    uint8_t g;
    uint8_t sect_esc_val, sect_bits;

    if (ics->window_sequence == EIGHT_SHORT_SEQUENCE)
        sect_bits = 3;
    else
        sect_bits = 5;
    sect_esc_val = (1<<sect_bits) - 1;

#if 0
    printf("\ntotal sfb %d\n", ics->max_sfb);
    printf("   sect    top     cb\n");
#endif

    for (g = 0; g < ics->num_window_groups; g++)
    {
        uint8_t k = 0;
        uint8_t i = 0;

        while (k < ics->max_sfb)