static int dpcm_decode_frame(AVCodecContext *avctx, void *data, int *data_size,

                             AVPacket *avpkt)

{

    const uint8_t *buf = avpkt->data;

    int buf_size = avpkt->size;

    const uint8_t *buf_end = buf + buf_size;

    DPCMContext *s = avctx->priv_data;

    int out = 0;

    int predictor[2];

    int ch = 0;

    int stereo = s->channels - 1;

    int16_t *output_samples = data;



    if (!buf_size)

        return 0;



    /* calculate output size */

    switch(avctx->codec->id) {

    case CODEC_ID_ROQ_DPCM:

        out = buf_size - 8;

        break;

    case CODEC_ID_INTERPLAY_DPCM:

        out = buf_size - 6 - s->channels;

        break;

    case CODEC_ID_XAN_DPCM:

        out = buf_size - 2 * s->channels;

        break;

    case CODEC_ID_SOL_DPCM:

        if (avctx->codec_tag != 3)

            out = buf_size * 2;

        else

            out = buf_size;

        break;

    }

    out *= av_get_bytes_per_sample(avctx->sample_fmt);

    if (out < 0) {

        av_log(avctx, AV_LOG_ERROR, "packet is too small\n");

        return AVERROR(EINVAL);

    }

    if (*data_size < out) {

        av_log(avctx, AV_LOG_ERROR, "output buffer is too small\n");

        return AVERROR(EINVAL);

    }



    switch(avctx->codec->id) {



    case CODEC_ID_ROQ_DPCM:

        buf += 6;



        if (stereo) {

            predictor[1] = (int16_t)(bytestream_get_byte(&buf) << 8);

            predictor[0] = (int16_t)(bytestream_get_byte(&buf) << 8);

        } else {

            predictor[0] = (int16_t)bytestream_get_le16(&buf);

        }



        /* decode the samples */

        while (buf < buf_end) {

            predictor[ch] += s->roq_square_array[*buf++];

            predictor[ch]  = av_clip_int16(predictor[ch]);

            *output_samples++ = predictor[ch];



            /* toggle channel */

            ch ^= stereo;

        }

        break;



    case CODEC_ID_INTERPLAY_DPCM:

        buf += 6;  /* skip over the stream mask and stream length */



        for (ch = 0; ch < s->channels; ch++) {

            predictor[ch] = (int16_t)bytestream_get_le16(&buf);

            *output_samples++ = predictor[ch];

        }



        ch = 0;

        while (buf < buf_end) {

            predictor[ch] += interplay_delta_table[*buf++];

            predictor[ch]  = av_clip_int16(predictor[ch]);

            *output_samples++ = predictor[ch];



            /* toggle channel */

            ch ^= stereo;

        }

        break;



    case CODEC_ID_XAN_DPCM:

    {

        int shift[2] = { 4, 4 };



        for (ch = 0; ch < s->channels; ch++)

            predictor[ch] = (int16_t)bytestream_get_le16(&buf);



        ch = 0;

        while (buf < buf_end) {

            uint8_t n = *buf++;

            int16_t diff = (n & 0xFC) << 8;

            if ((n & 0x03) == 3)

                shift[ch]++;

            else

                shift[ch] -= (2 * (n & 3));

            /* saturate the shifter to a lower limit of 0 */

            if (shift[ch] < 0)

                shift[ch] = 0;



            diff >>= shift[ch];

            predictor[ch] += diff;



            predictor[ch] = av_clip_int16(predictor[ch]);

            *output_samples++ = predictor[ch];



            /* toggle channel */

            ch ^= stereo;

        }

        break;

    }

    case CODEC_ID_SOL_DPCM:

        if (avctx->codec_tag != 3) {

            uint8_t *output_samples_u8 = data;

            while (buf < buf_end) {

                uint8_t n = *buf++;



                s->sample[0] += s->sol_table[n >> 4];

                s->sample[0]  = av_clip_uint8(s->sample[0]);

                *output_samples_u8++ = s->sample[0];



                s->sample[stereo] += s->sol_table[n & 0x0F];

                s->sample[stereo]  = av_clip_uint8(s->sample[stereo]);

                *output_samples_u8++ = s->sample[stereo];

            }

        } else {

            while (buf < buf_end) {

                uint8_t n = *buf++;

                if (n & 0x80) s->sample[ch] -= sol_table_16[n & 0x7F];

                else          s->sample[ch] += sol_table_16[n & 0x7F];

                s->sample[ch] = av_clip_int16(s->sample[ch]);

                *output_samples++ = s->sample[ch];

                /* toggle channel */

                ch ^= stereo;

            }

        }

        break;

    }



    *data_size = out;

    return buf_size;

}
