static int decode_tag(AVCodecContext * avctx,
                      void *data, int *data_size,
                      AVPacket *avpkt) {
    const uint8_t *buf = avpkt->data;
    int buf_size = avpkt->size;
    NellyMoserDecodeContext *s = avctx->priv_data;
    int blocks, i, block_size;
    int16_t* samples;
    samples = (int16_t*)data;

    if (buf_size < avctx->block_align) {
        *data_size = 0;
        return buf_size;
    }

    if (buf_size % 64) {
        av_log(avctx, AV_LOG_ERROR, "Tag size %d.\n", buf_size);
        *data_size = 0;
        return buf_size;
    }
    block_size = NELLY_SAMPLES * av_get_bytes_per_sample(avctx->sample_fmt);
    blocks     = FFMIN(buf_size / 64, *data_size / block_size);
    if (blocks <= 0) {
        av_log(avctx, AV_LOG_ERROR, "Output buffer is too small\n");
        return AVERROR(EINVAL);
    }
    /* Normal numbers of blocks for sample rates:
     *  8000 Hz - 1
     * 11025 Hz - 2
     * 16000 Hz - 3
     * 22050 Hz - 4
     * 44100 Hz - 8
     */

    for (i=0 ; i<blocks ; i++) {
        nelly_decode_block(s, &buf[i*NELLY_BLOCK_LEN], s->float_buf);
        s->fmt_conv.float_to_int16(&samples[i*NELLY_SAMPLES], s->float_buf, NELLY_SAMPLES);
    }
    *data_size = blocks * block_size;

    return buf_size;
}