static int find_slice_quant(AVCodecContext *avctx, const AVFrame *pic,
                            int trellis_node, int x, int y, int mbs_per_slice)
{
    ProresContext *ctx = avctx->priv_data;
    int i, q, pq, xp, yp;
    const uint16_t *src;
    int slice_width_factor = av_log2(mbs_per_slice);
    int num_cblocks[MAX_PLANES], pwidth;
    int plane_factor[MAX_PLANES], is_chroma[MAX_PLANES];
    const int min_quant = ctx->profile_info->min_quant;
    const int max_quant = ctx->profile_info->max_quant;
    int error, bits, bits_limit;
    int mbs, prev, cur, new_score;
    int slice_bits[TRELLIS_WIDTH], slice_score[TRELLIS_WIDTH];
    int overquant;
    uint16_t *qmat;

    mbs = x + mbs_per_slice;

    for (i = 0; i < ctx->num_planes; i++) {
        is_chroma[i]    = (i == 1 || i == 2);
        plane_factor[i] = slice_width_factor + 2;
        if (is_chroma[i])
            plane_factor[i] += ctx->chroma_factor - 3;
        if (!is_chroma[i] || ctx->chroma_factor == CFACTOR_Y444) {
            xp             = x << 4;
            yp             = y << 4;
            num_cblocks[i] = 4;
            pwidth         = avctx->width;
        } else {
            xp             = x << 3;
            yp             = y << 4;
            num_cblocks[i] = 2;
            pwidth         = avctx->width >> 1;
        }
        src = (const uint16_t*)(pic->data[i] + yp * pic->linesize[i]) + xp;

        get_slice_data(ctx, src, pic->linesize[i], xp, yp,
                       pwidth, avctx->height, ctx->blocks[i],
                       mbs_per_slice, num_cblocks[i]);
    }

    for (q = min_quant; q < max_quant + 2; q++) {
        ctx->nodes[trellis_node + q].prev_node = -1;
        ctx->nodes[trellis_node + q].quant     = q;
    }

    // todo: maybe perform coarser quantising to fit into frame size when needed
    for (q = min_quant; q <= max_quant; q++) {
        bits  = 0;
        error = 0;
        for (i = 0; i < ctx->num_planes; i++) {
            bits += estimate_slice_plane(ctx, &error, i,
                                         src, pic->linesize[i],
                                         mbs_per_slice,
                                         num_cblocks[i], plane_factor[i],
                                         ctx->quants[q]);
        }
        if (bits > 65000 * 8) {
            error = SCORE_LIMIT;
            break;
        }
        slice_bits[q]  = bits;
        slice_score[q] = error;
    }
    if (slice_bits[max_quant] <= ctx->bits_per_mb * mbs_per_slice) {
        slice_bits[max_quant + 1]  = slice_bits[max_quant];
        slice_score[max_quant + 1] = slice_score[max_quant] + 1;
        overquant = max_quant;
    } else {
        for (q = max_quant + 1; q < 128; q++) {
            bits  = 0;
            error = 0;
            if (q < MAX_STORED_Q) {
                qmat = ctx->quants[q];
            } else {
                qmat = ctx->custom_q;
                for (i = 0; i < 64; i++)
                    qmat[i] = ctx->profile_info->quant[i] * q;
            }
            for (i = 0; i < ctx->num_planes; i++) {
                bits += estimate_slice_plane(ctx, &error, i,
                                             src, pic->linesize[i],
                                             mbs_per_slice,
                                             num_cblocks[i], plane_factor[i],
                                             qmat);
            }
            if (bits <= ctx->bits_per_mb * mbs_per_slice)
                break;
        }

        slice_bits[max_quant + 1]  = bits;
        slice_score[max_quant + 1] = error;
        overquant = q;
    }
    ctx->nodes[trellis_node + max_quant + 1].quant = overquant;

    bits_limit = mbs * ctx->bits_per_mb;
    for (pq = min_quant; pq < max_quant + 2; pq++) {
        prev = trellis_node - TRELLIS_WIDTH + pq;

        for (q = min_quant; q < max_quant + 2; q++) {
            cur = trellis_node + q;

            bits  = ctx->nodes[prev].bits + slice_bits[q];
            error = slice_score[q];
            if (bits > bits_limit)
                error = SCORE_LIMIT;

            if (ctx->nodes[prev].score < SCORE_LIMIT && error < SCORE_LIMIT)
                new_score = ctx->nodes[prev].score + error;
            else
                new_score = SCORE_LIMIT;
            if (ctx->nodes[cur].prev_node == -1 ||
                ctx->nodes[cur].score >= new_score) {

                ctx->nodes[cur].bits      = bits;
                ctx->nodes[cur].score     = new_score;
                ctx->nodes[cur].prev_node = prev;
            }
        }
    }

    error = ctx->nodes[trellis_node + min_quant].score;
    pq    = trellis_node + min_quant;
    for (q = min_quant + 1; q < max_quant + 2; q++) {
        if (ctx->nodes[trellis_node + q].score <= error) {
            error = ctx->nodes[trellis_node + q].score;
            pq    = trellis_node + q;
        }
    }

    return pq;
}