VAR_ON            139 libavfilter/vf_perspective.c                                    [VAR_ON] = outlink->frame_count_in + 1 };
VAR_ON            170 libavfilter/vf_zoompan.c     var_values[VAR_ON] = outlink->frame_count_in;
VAR_ON            282 libavfilter/vf_zoompan.c         s->var_values[VAR_ON]    = outlink->frame_count_in;