alac.c

alac decoder,内容详细

            /* now read the number of samples,
             * as a 32bit integer */
            outputsamples = readbits(alac, 32);
            *outputsize = outputsamples * alac->bytespersample;
        }

        readsamplesize = alac->setinfo_sample_size - (wasted_bytes * 8);

        if (!isnotcompressed)
        { /* so it is compressed */
            int16_t predictor_coef_table[32];
            int predictor_coef_num;
            int prediction_type;
            int prediction_quantitization;
            int i;

            /* skip 16 bits, not sure what they are. seem to be used in
             * two channel case */
            readbits(alac, 8);
            readbits(alac, 8);

            prediction_type = readbits(alac, 4);
            prediction_quantitization = readbits(alac, 4);

            ricemodifier = readbits(alac, 3);
            predictor_coef_num = readbits(alac, 5);

            /* read the predictor table */
            for (i = 0; i < predictor_coef_num; i++)
            {
                predictor_coef_table[i] = (int16_t)readbits(alac, 16);
            }

            if (wasted_bytes)
            {
                /* these bytes seem to have something to do with
                 * > 2 channel files.
                 */
                fprintf(stderr, "FIXME: unimplemented, unhandling of wasted_bytes\n");
            }

            basterdised_rice_decompress(alac,
                                        alac->predicterror_buffer_a,
                                        outputsamples,
                                        readsamplesize,
                                        alac->setinfo_rice_initialhistory,
                                        alac->setinfo_rice_kmodifier,
                                        ricemodifier * alac->setinfo_rice_historymult / 4,
                                        (1 << alac->setinfo_rice_kmodifier) - 1);

            if (prediction_type == 0)
            { /* adaptive fir */
                predictor_decompress_fir_adapt(alac->predicterror_buffer_a,
                                               alac->outputsamples_buffer_a,
                                               outputsamples,
                                               readsamplesize,
                                               predictor_coef_table,
                                               predictor_coef_num,
                                               prediction_quantitization);
            }
            else
            {
                fprintf(stderr, "FIXME: unhandled predicition type: %i\n", prediction_type);
                /* i think the only other prediction type (or perhaps this is just a
                 * boolean?) runs adaptive fir twice.. like:
                 * predictor_decompress_fir_adapt(predictor_error, tempout, ...)
                 * predictor_decompress_fir_adapt(predictor_error, outputsamples ...)
                 * little strange..
                 */
            }

        }
        else
        { /* not compressed, easy case */
            if (readsamplesize <= 16)
            {
                int i;
                for (i = 0; i < outputsamples; i++)
                {
                    int32_t audiobits = readbits(alac, readsamplesize);

                    audiobits = SIGN_EXTENDED32(audiobits, readsamplesize);

                    alac->outputsamples_buffer_a[i] = audiobits;
                }
            }
            else
            {
                int i;
                for (i = 0; i < outputsamples; i++)
                {
                    int32_t audiobits;

                    audiobits = readbits(alac, 16);
                    /* special case of sign extension..
                     * as we'll be ORing the low 16bits into this */
                    audiobits = audiobits << 16;
                    audiobits = audiobits >> (32 - readsamplesize);

                    audiobits |= readbits(alac, readsamplesize - 16);

                    alac->outputsamples_buffer_a[i] = audiobits;
                }
            }
            /* wasted_bytes = 0; // unused */
        }

        switch(alac->setinfo_sample_size)
        {
        case 16:
        {
            int i;
            for (i = 0; i < outputsamples; i++)
            {
                int16_t sample = alac->outputsamples_buffer_a[i];
                if (host_bigendian)
                    _Swap16(sample);
                ((int16_t*)outbuffer)[i * alac->numchannels] = sample;
            }
            break;
        }
        case 20:
        case 24:
        case 32:
            fprintf(stderr, "FIXME: unimplemented sample size %i\n", alac->setinfo_sample_size);
            break;
        default:
            break;
        }
        break;
    }
    case 1: /* 2 channels */
    {
        int hassize;
        int isnotcompressed;
        int readsamplesize;

        int wasted_bytes;

        uint8_t interlacing_shift;
        uint8_t interlacing_leftweight;

        /* 2^result = something to do with output waiting.
         * perhaps matters if we read > 1 frame in a pass?
         */
        readbits(alac, 4);

        readbits(alac, 12); /* unknown, skip 12 bits */

        hassize = readbits(alac, 1); /* the output sample size is stored soon */

        wasted_bytes = readbits(alac, 2); /* unknown ? */

        isnotcompressed = readbits(alac, 1); /* whether the frame is compressed */

        if (hassize)
        {
            /* now read the number of samples,
             * as a 32bit integer */
            outputsamples = readbits(alac, 32);
            *outputsize = outputsamples * alac->bytespersample;
        }

        readsamplesize = alac->setinfo_sample_size - (wasted_bytes * 8) + 1;

        if (!isnotcompressed)
        { /* compressed */
            int16_t predictor_coef_table_a[32];
            int predictor_coef_num_a;
            int prediction_type_a;
            int prediction_quantitization_a;
            int ricemodifier_a;

            int16_t predictor_coef_table_b[32];
            int predictor_coef_num_b;
            int prediction_type_b;
            int prediction_quantitization_b;
            int ricemodifier_b;

            int i;

            interlacing_shift = readbits(alac, 8);
            interlacing_leftweight = readbits(alac, 8);

            /******** channel 1 ***********/
            prediction_type_a = readbits(alac, 4);
            prediction_quantitization_a = readbits(alac, 4);

            ricemodifier_a = readbits(alac, 3);
            predictor_coef_num_a = readbits(alac, 5);

            /* read the predictor table */
            for (i = 0; i < predictor_coef_num_a; i++)
            {
                predictor_coef_table_a[i] = (int16_t)readbits(alac, 16);
            }

            /******** channel 2 *********/
            prediction_type_b = readbits(alac, 4);
            prediction_quantitization_b = readbits(alac, 4);

            ricemodifier_b = readbits(alac, 3);
            predictor_coef_num_b = readbits(alac, 5);

            /* read the predictor table */
            for (i = 0; i < predictor_coef_num_b; i++)
            {
                predictor_coef_table_b[i] = (int16_t)readbits(alac, 16);
            }

            /*********************/
            if (wasted_bytes)
            { /* see mono case */
                fprintf(stderr, "FIXME: unimplemented, unhandling of wasted_bytes\n");
            }

            /* channel 1 */
            basterdised_rice_decompress(alac,
                                        alac->predicterror_buffer_a,
                                        outputsamples,
                                        readsamplesize,
                                        alac->setinfo_rice_initialhistory,
                                        alac->setinfo_rice_kmodifier,
                                        ricemodifier_a * alac->setinfo_rice_historymult / 4,
                                        (1 << alac->setinfo_rice_kmodifier) - 1);

            if (prediction_type_a == 0)
            { /* adaptive fir */
                predictor_decompress_fir_adapt(alac->predicterror_buffer_a,
                                               alac->outputsamples_buffer_a,
                                               outputsamples,
                                               readsamplesize,
                                               predictor_coef_table_a,
                                               predictor_coef_num_a,
                                               prediction_quantitization_a);
            }
            else
            { /* see mono case */
                fprintf(stderr, "FIXME: unhandled predicition type: %i\n", prediction_type_a);
            }

            /* channel 2 */
            basterdised_rice_decompress(alac,
                                        alac->predicterror_buffer_b,
                                        outputsamples,
                                        readsamplesize,
                                        alac->setinfo_rice_initialhistory,
                                        alac->setinfo_rice_kmodifier,
                                        ricemodifier_b * alac->setinfo_rice_historymult / 4,
                                        (1 << alac->setinfo_rice_kmodifier) - 1);

            if (prediction_type_b == 0)
            { /* adaptive fir */
                predictor_decompress_fir_adapt(alac->predicterror_buffer_b,
                                               alac->outputsamples_buffer_b,
                                               outputsamples,
                                               readsamplesize,
                                               predictor_coef_table_b,
                                               predictor_coef_num_b,
                                               prediction_quantitization_b);
            }
            else
            {
                fprintf(stderr, "FIXME: unhandled predicition type: %i\n", prediction_type_b);
            }
        }
        else
        { /* not compressed, easy case */
            if (alac->setinfo_sample_size <= 16)
            {
                int i;
                for (i = 0; i < outputsamples; i++)
                {
                    int32_t audiobits_a, audiobits_b;

                    audiobits_a = readbits(alac, alac->setinfo_sample_size);
                    audiobits_b = readbits(alac, alac->setinfo_sample_size);

                    audiobits_a = SIGN_EXTENDED32(audiobits_a, alac->setinfo_sample_size);
                    audiobits_b = SIGN_EXTENDED32(audiobits_b, alac->setinfo_sample_size);

                    alac->outputsamples_buffer_a[i] = audiobits_a;
                    alac->outputsamples_buffer_b[i] = audiobits_b;
                }
            }
            else
            {
                int i;
                for (i = 0; i < outputsamples; i++)
                {
                    int32_t audiobits_a, audiobits_b;

                    audiobits_a = readbits(alac, 16);
                    audiobits_a = audiobits_a << 16;
                    audiobits_a = audiobits_a >> (32 - alac->setinfo_sample_size);
                    audiobits_a |= readbits(alac, alac->setinfo_sample_size - 16);

                    audiobits_b = readbits(alac, 16);
                    audiobits_b = audiobits_b << 16;
                    audiobits_b = audiobits_b >> (32 - alac->setinfo_sample_size);
                    audiobits_b |= readbits(alac, alac->setinfo_sample_size - 16);

                    alac->outputsamples_buffer_a[i] = audiobits_a;
                    alac->outputsamples_buffer_b[i] = audiobits_b;
                }
            }
            /* wasted_bytes = 0; */
            interlacing_shift = 0;
            interlacing_leftweight = 0;
        }

        switch(alac->setinfo_sample_size)
        {
        case 16:
        {
            deinterlace_16(alac->outputsamples_buffer_a,
                           alac->outputsamples_buffer_b,
                           (int16_t*)outbuffer,
                           alac->numchannels,
                           outputsamples,
                           interlacing_shift,
                           interlacing_leftweight);
            break;
        }
        case 20:
        case 24:
        case 32:
            fprintf(stderr, "FIXME: unimplemented sample size %i\n", alac->setinfo_sample_size);
            break;
        default:
            break;
        }

        break;
    }
    }
}

alac_file *create_alac(int samplesize, int numchannels)
{
    alac_file *newfile = malloc(sizeof(alac_file));

    newfile->samplesize = samplesize;
    newfile->numchannels = numchannels;
    newfile->bytespersample = (samplesize / 8) * numchannels;

    return newfile;
}