static int tta_decode_frame(AVCodecContext *avctx,
        void *data, int *data_size,
        AVPacket *avpkt)
{
    const uint8_t *buf = avpkt->data;
    int buf_size = avpkt->size;
    TTAContext *s = avctx->priv_data;
    int i;

    init_get_bits(&s->gb, buf, buf_size*8);
    {
        int cur_chan = 0, framelen = s->frame_length;
        int32_t *p;

        // FIXME: seeking
        s->total_frames--;
        if (!s->total_frames && s->last_frame_length)
            framelen = s->last_frame_length;

        if (*data_size < (framelen * s->channels * 2)) {
            av_log(avctx, AV_LOG_ERROR, "Output buffer size is too small.\n");
            return -1;
        }

        // init per channel states
        for (i = 0; i < s->channels; i++) {
            s->ch_ctx[i].predictor = 0;
            ttafilter_init(&s->ch_ctx[i].filter, ttafilter_configs[s->bps-1][0], ttafilter_configs[s->bps-1][1]);
            rice_init(&s->ch_ctx[i].rice, 10, 10);
        }

        for (p = s->decode_buffer; p < s->decode_buffer + (framelen * s->channels); p++) {
            int32_t *predictor = &s->ch_ctx[cur_chan].predictor;
            TTAFilter *filter = &s->ch_ctx[cur_chan].filter;
            TTARice *rice = &s->ch_ctx[cur_chan].rice;
            uint32_t unary, depth, k;
            int32_t value;

            unary = tta_get_unary(&s->gb);

            if (unary == 0) {
                depth = 0;
                k = rice->k0;
            } else {
                depth = 1;
                k = rice->k1;
                unary--;
            }

            if (get_bits_left(&s->gb) < k)
                return -1;

            if (k) {
                if (k > MIN_CACHE_BITS)
                    return -1;
                value = (unary << k) + get_bits(&s->gb, k);
            } else
                value = unary;

            // FIXME: copy paste from original
            switch (depth) {
            case 1:
                rice->sum1 += value - (rice->sum1 >> 4);
                if (rice->k1 > 0 && rice->sum1 < shift_16[rice->k1])
                    rice->k1--;
                else if(rice->sum1 > shift_16[rice->k1 + 1])
                    rice->k1++;
                value += shift_1[rice->k0];
            default:
                rice->sum0 += value - (rice->sum0 >> 4);
                if (rice->k0 > 0 && rice->sum0 < shift_16[rice->k0])
                    rice->k0--;
                else if(rice->sum0 > shift_16[rice->k0 + 1])
                    rice->k0++;
            }

            // extract coded value
#define UNFOLD(x) (((x)&1) ? (++(x)>>1) : (-(x)>>1))
            *p = UNFOLD(value);

            // run hybrid filter
            ttafilter_process(filter, p, 0);

            // fixed order prediction
#define PRED(x, k) (int32_t)((((uint64_t)x << k) - x) >> k)
            switch (s->bps) {
                case 1: *p += PRED(*predictor, 4); break;
                case 2:
                case 3: *p += PRED(*predictor, 5); break;
                case 4: *p += *predictor; break;
            }
            *predictor = *p;

            // flip channels
            if (cur_chan < (s->channels-1))
                cur_chan++;
            else {
                // decorrelate in case of stereo integer
                if (s->channels > 1) {
                    int32_t *r = p - 1;
                    for (*p += *r / 2; r > p - s->channels; r--)
                        *r = *(r + 1) - *r;
                }
                cur_chan = 0;
            }
        }

        if (get_bits_left(&s->gb) < 32)
            return -1;
        skip_bits(&s->gb, 32); // frame crc

        // convert to output buffer
        switch(s->bps) {
            case 2: {
                uint16_t *samples = data;
                for (p = s->decode_buffer; p < s->decode_buffer + (framelen * s->channels); p++) {
                    *samples++ = *p;
                }
                *data_size = (uint8_t *)samples - (uint8_t *)data;
                break;
            }
            default:
                av_log(s->avctx, AV_LOG_ERROR, "Error, only 16bit samples supported!\n");
        }
    }

    return buf_size;
}