static void end_frame(AVFilterLink *inlink)
{
    AVFilterContext   *ctx        = inlink->dst;
    FieldOrderContext *fieldorder = ctx->priv;
    AVFilterLink      *outlink    = ctx->outputs[0];

    AVFilterBufferRef *inpicref   = inlink->cur_buf;
    AVFilterBufferRef *outpicref  = outlink->out_buf;

    int               h, plane, line_step, line_size, line;
    uint8_t           *cpy_src, *cpy_dst;

    if (    inpicref->video->interlaced
         && inpicref->video->top_field_first != fieldorder->dst_tff) {
        av_dlog(ctx,
                "picture will move %s one line\n",
                fieldorder->dst_tff ? "up" : "down");
        h = inpicref->video->h;
        for (plane = 0; plane < 4 && inpicref->data[plane]; plane++) {
            line_step = inpicref->linesize[plane];
            line_size = fieldorder->line_size[plane];
            cpy_src = inpicref->data[plane];
            cpy_dst = outpicref->data[plane];
            if (fieldorder->dst_tff) {
                /** Move every line up one line, working from
                 *  the top to the bottom of the frame.
                 *  The original top line is lost.
                 *  The new last line is created as a copy of the
                 *  penultimate line from that field. */
                for (line = 0; line < h; line++) {
                    if (1 + line < outpicref->video->h) {
                        memcpy(cpy_dst, cpy_src + line_step, line_size);
                    } else {
                        memcpy(cpy_dst, cpy_src - line_step - line_step, line_size);
                    }
                    cpy_src += line_step;
                    cpy_dst += line_step;
                }
            } else {
                /** Move every line down one line, working from
                 *  the bottom to the top of the frame.
                 *  The original bottom line is lost.
                 *  The new first line is created as a copy of the
                 *  second line from that field. */
                cpy_src += (h - 1) * line_step;
                cpy_dst += (h - 1) * line_step;
                for (line = h - 1; line >= 0 ; line--) {
                    if (line > 0) {
                        memcpy(cpy_dst, cpy_src - line_step, line_size);
                    } else {
                        memcpy(cpy_dst, cpy_src + line_step + line_step, line_size);
                    }
                    cpy_src -= line_step;
                    cpy_dst -= line_step;
                }
            }
        }
        outpicref->video->top_field_first = fieldorder->dst_tff;
        ff_draw_slice(outlink, 0, h, 1);
    } else {
        av_dlog(ctx,
                "not interlaced or field order already correct\n");
    }

    ff_end_frame(outlink);
    avfilter_unref_bufferp(&outlink->out_buf);
}