static void await_references(H264Context *h)
{
    const int mb_xy   = h->mb_xy;
    const int mb_type = h->cur_pic.mb_type[mb_xy];
    int refs[2][48];
    int nrefs[2] = { 0 };
    int ref, list;

    memset(refs, -1, sizeof(refs));

    if (IS_16X16(mb_type)) {
        get_lowest_part_y(h, refs, 0, 16, 0,
                          IS_DIR(mb_type, 0, 0), IS_DIR(mb_type, 0, 1), nrefs);
    } else if (IS_16X8(mb_type)) {
        get_lowest_part_y(h, refs, 0, 8, 0,
                          IS_DIR(mb_type, 0, 0), IS_DIR(mb_type, 0, 1), nrefs);
        get_lowest_part_y(h, refs, 8, 8, 8,
                          IS_DIR(mb_type, 1, 0), IS_DIR(mb_type, 1, 1), nrefs);
    } else if (IS_8X16(mb_type)) {
        get_lowest_part_y(h, refs, 0, 16, 0,
                          IS_DIR(mb_type, 0, 0), IS_DIR(mb_type, 0, 1), nrefs);
        get_lowest_part_y(h, refs, 4, 16, 0,
                          IS_DIR(mb_type, 1, 0), IS_DIR(mb_type, 1, 1), nrefs);
    } else {
        int i;

        assert(IS_8X8(mb_type));

        for (i = 0; i < 4; i++) {
            const int sub_mb_type = h->sub_mb_type[i];
            const int n           = 4 * i;
            int y_offset          = (i & 2) << 2;

            if (IS_SUB_8X8(sub_mb_type)) {
                get_lowest_part_y(h, refs, n, 8, y_offset,
                                  IS_DIR(sub_mb_type, 0, 0),
                                  IS_DIR(sub_mb_type, 0, 1),
                                  nrefs);
            } else if (IS_SUB_8X4(sub_mb_type)) {
                get_lowest_part_y(h, refs, n, 4, y_offset,
                                  IS_DIR(sub_mb_type, 0, 0),
                                  IS_DIR(sub_mb_type, 0, 1),
                                  nrefs);
                get_lowest_part_y(h, refs, n + 2, 4, y_offset + 4,
                                  IS_DIR(sub_mb_type, 0, 0),
                                  IS_DIR(sub_mb_type, 0, 1),
                                  nrefs);
            } else if (IS_SUB_4X8(sub_mb_type)) {
                get_lowest_part_y(h, refs, n, 8, y_offset,
                                  IS_DIR(sub_mb_type, 0, 0),
                                  IS_DIR(sub_mb_type, 0, 1),
                                  nrefs);
                get_lowest_part_y(h, refs, n + 1, 8, y_offset,
                                  IS_DIR(sub_mb_type, 0, 0),
                                  IS_DIR(sub_mb_type, 0, 1),
                                  nrefs);
            } else {
                int j;
                assert(IS_SUB_4X4(sub_mb_type));
                for (j = 0; j < 4; j++) {
                    int sub_y_offset = y_offset + 2 * (j & 2);
                    get_lowest_part_y(h, refs, n + j, 4, sub_y_offset,
                                      IS_DIR(sub_mb_type, 0, 0),
                                      IS_DIR(sub_mb_type, 0, 1),
                                      nrefs);
                }
            }
        }
    }

    for (list = h->list_count - 1; list >= 0; list--)
        for (ref = 0; ref < 48 && nrefs[list]; ref++) {
            int row = refs[list][ref];
            if (row >= 0) {
                Picture *ref_pic      = &h->ref_list[list][ref];
                int ref_field         = ref_pic->reference - 1;
                int ref_field_picture = ref_pic->field_picture;
                int pic_height        = 16 * h->mb_height >> ref_field_picture;

                row <<= MB_MBAFF(h);
                nrefs[list]--;

                if (!FIELD_PICTURE(h) && ref_field_picture) { // frame referencing two fields
                    ff_thread_await_progress(&ref_pic->tf,
                                             FFMIN((row >> 1) - !(row & 1),
                                                   pic_height - 1),
                                             1);
                    ff_thread_await_progress(&ref_pic->tf,
                                             FFMIN((row >> 1), pic_height - 1),
                                             0);
                } else if (FIELD_PICTURE(h) && !ref_field_picture) { // field referencing one field of a frame
                    ff_thread_await_progress(&ref_pic->tf,
                                             FFMIN(row * 2 + ref_field,
                                                   pic_height - 1),
                                             0);
                } else if (FIELD_PICTURE(h)) {
                    ff_thread_await_progress(&ref_pic->tf,
                                             FFMIN(row, pic_height - 1),
                                             ref_field);
                } else {
                    ff_thread_await_progress(&ref_pic->tf,
                                             FFMIN(row, pic_height - 1),
                                             0);
                }
            }
        }
}