lavfi/settb: rescale input frame durations

libavfilter/settb.c

@@ -128,6 +128,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
     AVFilterLink *outlink = ctx->outputs[0];
 
     frame->pts = rescale_pts(inlink, outlink, frame->pts);
+    frame->duration = av_rescale_q(frame->duration, inlink->time_base, outlink->time_base);
 
     return ff_filter_frame(outlink, frame);
 }