Do it without asking

demo.scm

@@ -8,6 +8,6 @@
 (define graph1 (generate-web 10 10))
 (define graph2
   (~> (copy-tree graph1)
-      (remove-rect 10 3 3 4 5)
-      (remove-rect 10 3 3 6 4)))
+      (remove-rect 10 1 3 6 3)
+      (remove-rect 10 6 3 6 7)))
 (write-graphs-to-file (vector graph1 graph2) "graph.webp")

graphgif.scm

@@ -148,7 +148,8 @@
       surface
       (string-append pngdir "/img-" (number->string i) ".png")))
    surfaces)
-  (system* "ffmpeg" "-i" (string-append pngdir "/img-%d.png")
+  (system* "ffmpeg" "-y"
+	   "-i" (string-append pngdir "/img-%d.png")
 	   "-r" "1" "-loop" "0" filename))
 
 (define-public (write-graphs-to-file graphs filename)