FFmpeg/libavcodec/alac.c

/*
 * ALAC (Apple Lossless Audio Codec) decoder
 * Copyright (c) 2005 David Hammerton
 * All rights reserved.
 *
 * 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 alac.c
 * ALAC (Apple Lossless Audio Codec) decoder
 * @author 2005 David Hammerton
 *
 * For more information on the ALAC format, visit:
 *  http://crazney.net/programs/itunes/alac.html
 *
 * Note: This decoder expects a 36- (0x24-)byte QuickTime atom to be
 * passed through the extradata[_size] fields. This atom is tacked onto
 * the end of an 'alac' stsd atom and has the following format:
 *  bytes 0-3   atom size (0x24), big-endian
 *  bytes 4-7   atom type ('alac', not the 'alac' tag from start of stsd)
 *  bytes 8-35  data bytes needed by decoder
 *
 * Extradata:
 * 32bit  size
 * 32bit  tag (=alac)
 * 32bit  zero?
 * 32bit  max sample per frame
 *  8bit  ?? (zero?)
 *  8bit  sample size
 *  8bit  history mult
 *  8bit  initial history
 *  8bit  kmodifier
 *  8bit  channels?
 * 16bit  ??
 * 32bit  max coded frame size
 * 32bit  bitrate?
 * 32bit  samplerate
 */


#include "avcodec.h"
#include "bitstream.h"

#define ALAC_EXTRADATA_SIZE 36

typedef struct {

    AVCodecContext *avctx;
    GetBitContext gb;
    /* init to 0; first frame decode should initialize from extradata and
     * set this to 1 */
    int context_initialized;

    int samplesize;
    int numchannels;
    int bytespersample;

    /* buffers */
    int32_t *predicterror_buffer_a;
    int32_t *predicterror_buffer_b;

    int32_t *outputsamples_buffer_a;
    int32_t *outputsamples_buffer_b;

    /* stuff from setinfo */
    uint32_t setinfo_max_samples_per_frame; /* 0x1000 = 4096 */    /* max samples per frame? */
    uint8_t setinfo_7a; /* 0x00 */
    uint8_t setinfo_sample_size; /* 0x10 */
    uint8_t setinfo_rice_historymult; /* 0x28 */
    uint8_t setinfo_rice_initialhistory; /* 0x0a */
    uint8_t setinfo_rice_kmodifier; /* 0x0e */
    uint8_t setinfo_7f; /* 0x02 */
    uint16_t setinfo_80; /* 0x00ff */
    uint32_t setinfo_82; /* 0x000020e7 */
    uint32_t setinfo_86; /* 0x00069fe4 */
    uint32_t setinfo_8a_rate; /* 0x0000ac44 */
    /* end setinfo stuff */

} ALACContext;

static void allocate_buffers(ALACContext *alac)
{
    alac->predicterror_buffer_a = av_malloc(alac->setinfo_max_samples_per_frame * 4);
    alac->predicterror_buffer_b = av_malloc(alac->setinfo_max_samples_per_frame * 4);

    alac->outputsamples_buffer_a = av_malloc(alac->setinfo_max_samples_per_frame * 4);
    alac->outputsamples_buffer_b = av_malloc(alac->setinfo_max_samples_per_frame * 4);
}

static int alac_set_info(ALACContext *alac)
{
    unsigned char *ptr = alac->avctx->extradata;

    ptr += 4; /* size */
    ptr += 4; /* alac */
    ptr += 4; /* 0 ? */

    if(AV_RB32(ptr) >= UINT_MAX/4){
        av_log(alac->avctx, AV_LOG_ERROR, "setinfo_max_samples_per_frame too large\n");
        return -1;
    }
    alac->setinfo_max_samples_per_frame = AV_RB32(ptr); /* buffer size / 2 ? */
    ptr += 4;
    alac->setinfo_7a = *ptr++;
    alac->setinfo_sample_size = *ptr++;
    alac->setinfo_rice_historymult = *ptr++;
    alac->setinfo_rice_initialhistory = *ptr++;
    alac->setinfo_rice_kmodifier = *ptr++;
    alac->setinfo_7f = *ptr++; // channels?
    alac->setinfo_80 = AV_RB16(ptr);
    ptr += 2;
    alac->setinfo_82 = AV_RB32(ptr); // max coded frame size
    ptr += 4;
    alac->setinfo_86 = AV_RB32(ptr); // bitrate ?
    ptr += 4;
    alac->setinfo_8a_rate = AV_RB32(ptr); // samplerate
    ptr += 4;

    allocate_buffers(alac);

    return 0;
}

/* hideously inefficient. could use a bitmask search,
 * alternatively bsr on x86,
 */
static int count_leading_zeros(int32_t input)
{
    int i = 0;
    while (!(0x80000000 & input) && i < 32) {
        i++;
        input = input << 1;
    }
    return i;
}

static void bastardized_rice_decompress(ALACContext *alac,
                                 int32_t *output_buffer,
                                 int output_size,
                                 int readsamplesize, /* arg_10 */
                                 int rice_initialhistory, /* arg424->b */
                                 int rice_kmodifier, /* arg424->d */
                                 int rice_historymult, /* arg424->c */
                                 int rice_kmodifier_mask /* arg424->e */
        )
{
    int output_count;
    unsigned int history = rice_initialhistory;
    int sign_modifier = 0;

    for (output_count = 0; output_count < output_size; output_count++) {
        int32_t x = 0;
        int32_t x_modified;
        int32_t final_val;

        /* read x - number of 1s before 0 represent the rice */
        while (x <= 8 && get_bits1(&alac->gb)) {
            x++;
        }


        if (x > 8) { /* RICE THRESHOLD */
          /* use alternative encoding */
            int32_t value;

            value = get_bits(&alac->gb, readsamplesize);

            /* mask value to readsamplesize size */
            if (readsamplesize != 32)
                value &= (0xffffffff >> (32 - readsamplesize));

            x = value;
        } else {
          /* standard rice encoding */
            int extrabits;
            int k; /* size of extra bits */

            /* read k, that is bits as is */
            k = 31 - rice_kmodifier - count_leading_zeros((history >> 9) + 3);

            if (k < 0)
                k += rice_kmodifier;
            else
                k = rice_kmodifier;

            if (k != 1) {
                extrabits = show_bits(&alac->gb, k);

                /* multiply x by 2^k - 1, as part of their strange algorithm */
                x = (x << k) - x;

                if (extrabits > 1) {
                    x += extrabits - 1;
                    get_bits(&alac->gb, k);
                } else {
                    get_bits(&alac->gb, k - 1);
                }
            }
        }

        x_modified = sign_modifier + x;
        final_val = (x_modified + 1) / 2;
        if (x_modified & 1) final_val *= -1;

        output_buffer[output_count] = final_val;

        sign_modifier = 0;

        /* now update the history */
        history += (x_modified * rice_historymult)
                 - ((history * rice_historymult) >> 9);

        if (x_modified > 0xffff)
            history = 0xffff;

        /* special case: there may be compressed blocks of 0 */
        if ((history < 128) && (output_count+1 < output_size)) {
            int block_size;

            sign_modifier = 1;

            x = 0;
            while (x <= 8 && get_bits1(&alac->gb)) {
                x++;
            }

            if (x > 8) {
                block_size = get_bits(&alac->gb, 16);
                block_size &= 0xffff;
            } else {
                int k;
                int extrabits;

                k = count_leading_zeros(history) + ((history + 16) >> 6 /* / 64 */) - 24;

                extrabits = show_bits(&alac->gb, k);

                block_size = (((1 << k) - 1) & rice_kmodifier_mask) * x
                           + extrabits - 1;

                if (extrabits < 2) {
                    x = 1 - extrabits;
                    block_size += x;
                    get_bits(&alac->gb, k - 1);
                } else {
                    get_bits(&alac->gb, k);
                }
            }

            if (block_size > 0) {
                memset(&output_buffer[output_count+1], 0, block_size * 4);
                output_count += block_size;

            }

            if (block_size > 0xffff)
                sign_modifier = 0;

            history = 0;
        }
    }
}

#define SIGN_EXTENDED32(val, bits) ((val << (32 - bits)) >> (32 - bits))

#define SIGN_ONLY(v) \
                     ((v < 0) ? (-1) : \
                                ((v > 0) ? (1) : \
                                           (0)))

static void predictor_decompress_fir_adapt(int32_t *error_buffer,
                                           int32_t *buffer_out,
                                           int output_size,
                                           int readsamplesize,
                                           int16_t *predictor_coef_table,
                                           int predictor_coef_num,
                                           int predictor_quantitization)
{
    int i;

    /* first sample always copies */
    *buffer_out = *error_buffer;

    if (!predictor_coef_num) {
        if (output_size <= 1) return;
        memcpy(buffer_out+1, error_buffer+1, (output_size-1) * 4);
        return;
    }

    if (predictor_coef_num == 0x1f) { /* 11111 - max value of predictor_coef_num */
      /* second-best case scenario for fir decompression,
       * error describes a small difference from the previous sample only
       */
        if (output_size <= 1) return;
        for (i = 0; i < output_size - 1; i++) {
            int32_t prev_value;
            int32_t error_value;

            prev_value = buffer_out[i];
            error_value = error_buffer[i+1];
            buffer_out[i+1] = SIGN_EXTENDED32((prev_value + error_value), readsamplesize);
        }
        return;
    }

    /* read warm-up samples */
    if (predictor_coef_num > 0) {
        int i;
        for (i = 0; i < predictor_coef_num; i++) {
            int32_t val;

            val = buffer_out[i] + error_buffer[i+1];

            val = SIGN_EXTENDED32(val, readsamplesize);

            buffer_out[i+1] = val;
        }
    }

#if 0
    /* 4 and 8 are very common cases (the only ones i've seen). these
     * should be unrolled and optimised
     */
    if (predictor_coef_num == 4) {
        /* FIXME: optimised general case */
        return;
    }

    if (predictor_coef_table == 8) {
        /* FIXME: optimised general case */
        return;
    }
#endif


    /* general case */
    if (predictor_coef_num > 0) {
        for (i = predictor_coef_num + 1;
             i < output_size;
             i++) {
            int j;
            int sum = 0;
            int outval;
            int error_val = error_buffer[i];

            for (j = 0; j < predictor_coef_num; j++) {
                sum += (buffer_out[predictor_coef_num-j] - buffer_out[0]) *
                       predictor_coef_table[j];
            }

            outval = (1 << (predictor_quantitization-1)) + sum;
            outval = outval >> predictor_quantitization;
            outval = outval + buffer_out[0] + error_val;
            outval = SIGN_EXTENDED32(outval, readsamplesize);

            buffer_out[predictor_coef_num+1] = outval;

            if (error_val > 0) {
                int predictor_num = predictor_coef_num - 1;

                while (predictor_num >= 0 && error_val > 0) {
                    int val = buffer_out[0] - buffer_out[predictor_coef_num - predictor_num];
                    int sign = SIGN_ONLY(val);

                    predictor_coef_table[predictor_num] -= sign;

                    val *= sign; /* absolute value */

                    error_val -= ((val >> predictor_quantitization) *
                                  (predictor_coef_num - predictor_num));

                    predictor_num--;
                }
            } else if (error_val < 0) {
                int predictor_num = predictor_coef_num - 1;

                while (predictor_num >= 0 && error_val < 0) {
                    int val = buffer_out[0] - buffer_out[predictor_coef_num - predictor_num];
                    int sign = - SIGN_ONLY(val);

                    predictor_coef_table[predictor_num] -= sign;

                    val *= sign; /* neg value */

                    error_val -= ((val >> predictor_quantitization) *
                                  (predictor_coef_num - predictor_num));

                    predictor_num--;
                }
            }

            buffer_out++;
        }
    }
}

static void deinterlace_16(int32_t *buffer_a, int32_t *buffer_b,
                    int16_t *buffer_out,
                    int numchannels, int numsamples,
                    uint8_t interlacing_shift,
                    uint8_t interlacing_leftweight)
{
    int i;
    if (numsamples <= 0) return;

    /* weighted interlacing */
    if (interlacing_leftweight) {
        for (i = 0; i < numsamples; i++) {
            int32_t difference, midright;
            int16_t left;
            int16_t right;

            midright = buffer_a[i];
            difference = buffer_b[i];


            right = midright - ((difference * interlacing_leftweight) >> interlacing_shift);
            left = (midright - ((difference * interlacing_leftweight) >> interlacing_shift))
                 + difference;

            buffer_out[i*numchannels] = left;
            buffer_out[i*numchannels + 1] = right;
        }

        return;
    }

    /* otherwise basic interlacing took place */
    for (i = 0; i < numsamples; i++) {
        int16_t left, right;

        left = buffer_a[i];
        right = buffer_b[i];

        buffer_out[i*numchannels] = left;
        buffer_out[i*numchannels + 1] = right;
    }
}

static int alac_decode_frame(AVCodecContext *avctx,
                             void *outbuffer, int *outputsize,
                             uint8_t *inbuffer, int input_buffer_size)
{
    ALACContext *alac = avctx->priv_data;

    int channels;
    int32_t outputsamples;

    /* short-circuit null buffers */
    if (!inbuffer || !input_buffer_size)
        return input_buffer_size;

    /* initialize from the extradata */
    if (!alac->context_initialized) {
        if (alac->avctx->extradata_size != ALAC_EXTRADATA_SIZE) {
            av_log(avctx, AV_LOG_ERROR, "alac: expected %d extradata bytes\n",
                ALAC_EXTRADATA_SIZE);
            return input_buffer_size;
        }
        if (alac_set_info(alac)) {
            av_log(avctx, AV_LOG_ERROR, "alac: set_info failed\n");
            return input_buffer_size;
        }
        alac->context_initialized = 1;
    }

    outputsamples = alac->setinfo_max_samples_per_frame;

    init_get_bits(&alac->gb, inbuffer, input_buffer_size * 8);

    channels = get_bits(&alac->gb, 3);

    *outputsize = outputsamples * alac->bytespersample;

    switch(channels) {
    case 0: { /* 1 channel */
        int hassize;
        int isnotcompressed;
        int readsamplesize;

        int wasted_bytes;
        int ricemodifier;


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

        get_bits(&alac->gb, 12); /* unknown, skip 12 bits */

        hassize = get_bits(&alac->gb, 1); /* the output sample size is stored soon */

        wasted_bytes = get_bits(&alac->gb, 2); /* unknown ? */

        isnotcompressed = get_bits(&alac->gb, 1); /* whether the frame is compressed */

        if (hassize) {
            /* now read the number of samples,
             * as a 32bit integer */
            outputsamples = get_bits(&alac->gb, 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;

            /* FIXME: skip 16 bits, not sure what they are. seem to be used in
             * two channel case */
            get_bits(&alac->gb, 8);
            get_bits(&alac->gb, 8);

            prediction_type = get_bits(&alac->gb, 4);
            prediction_quantitization = get_bits(&alac->gb, 4);

            ricemodifier = get_bits(&alac->gb, 3);
            predictor_coef_num = get_bits(&alac->gb, 5);

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

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

            bastardized_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 {
                av_log(avctx, AV_LOG_ERROR, "FIXME: unhandled prediction 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 = get_bits(&alac->gb, 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 = get_bits(&alac->gb, 16);
                    /* special case of sign extension..
                     * as we'll be ORing the low 16bits into this */
                    audiobits = audiobits << 16;
                    audiobits = audiobits >> (32 - readsamplesize);

                    audiobits |= get_bits(&alac->gb, 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];
                ((int16_t*)outbuffer)[i * alac->numchannels] = sample;
            }
            break;
        }
        case 20:
        case 24:
        case 32:
            av_log(avctx, AV_LOG_ERROR, "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?
         */
        get_bits(&alac->gb, 4);

        get_bits(&alac->gb, 12); /* unknown, skip 12 bits */

        hassize = get_bits(&alac->gb, 1); /* the output sample size is stored soon */

        wasted_bytes = get_bits(&alac->gb, 2); /* unknown ? */

        isnotcompressed = get_bits(&alac->gb, 1); /* whether the frame is compressed */

        if (hassize) {
            /* now read the number of samples,
             * as a 32bit integer */
            outputsamples = get_bits(&alac->gb, 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 = get_bits(&alac->gb, 8);
            interlacing_leftweight = get_bits(&alac->gb, 8);

            /******** channel 1 ***********/
            prediction_type_a = get_bits(&alac->gb, 4);
            prediction_quantitization_a = get_bits(&alac->gb, 4);

            ricemodifier_a = get_bits(&alac->gb, 3);
            predictor_coef_num_a = get_bits(&alac->gb, 5);

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

            /******** channel 2 *********/
            prediction_type_b = get_bits(&alac->gb, 4);
            prediction_quantitization_b = get_bits(&alac->gb, 4);

            ricemodifier_b = get_bits(&alac->gb, 3);
            predictor_coef_num_b = get_bits(&alac->gb, 5);

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

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

            /* channel 1 */
            bastardized_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 */
                av_log(avctx, AV_LOG_ERROR, "FIXME: unhandled prediction type: %i\n", prediction_type_a);
            }

            /* channel 2 */
            bastardized_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 {
                av_log(avctx, AV_LOG_ERROR, "FIXME: unhandled prediction 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 = get_bits(&alac->gb, alac->setinfo_sample_size);
                    audiobits_b = get_bits(&alac->gb, 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 = get_bits(&alac->gb, 16);
                    audiobits_a = audiobits_a << 16;
                    audiobits_a = audiobits_a >> (32 - alac->setinfo_sample_size);
                    audiobits_a |= get_bits(&alac->gb, alac->setinfo_sample_size - 16);

                    audiobits_b = get_bits(&alac->gb, 16);
                    audiobits_b = audiobits_b << 16;
                    audiobits_b = audiobits_b >> (32 - alac->setinfo_sample_size);
                    audiobits_b |= get_bits(&alac->gb, 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:
            av_log(avctx, AV_LOG_ERROR, "FIXME: unimplemented sample size %i\n", alac->setinfo_sample_size);
            break;
        default:
            break;
        }

        break;
    }
    }

    return input_buffer_size;
}

static int alac_decode_init(AVCodecContext * avctx)
{
    ALACContext *alac = avctx->priv_data;
    alac->avctx = avctx;
    alac->context_initialized = 0;

    alac->samplesize = alac->avctx->bits_per_sample;
    alac->numchannels = alac->avctx->channels;
    alac->bytespersample = (alac->samplesize / 8) * alac->numchannels;

    return 0;
}

static int alac_decode_close(AVCodecContext *avctx)
{
    ALACContext *alac = avctx->priv_data;

    av_free(alac->predicterror_buffer_a);
    av_free(alac->predicterror_buffer_b);

    av_free(alac->outputsamples_buffer_a);
    av_free(alac->outputsamples_buffer_b);

    return 0;
}

AVCodec alac_decoder = {
    "alac",
    CODEC_TYPE_AUDIO,
    CODEC_ID_ALAC,
    sizeof(ALACContext),
    alac_decode_init,
    NULL,
    alac_decode_close,
    alac_decode_frame,
};