Fix division by zero on some video/GIF files (#30600)

app/lib/video_metadata_extractor.rb

@@ -41,8 +41,8 @@ class VideoMetadataExtractor
         @colorspace  = video_stream[:pix_fmt]
         @width       = video_stream[:width]
         @height      = video_stream[:height]
-        @frame_rate  = video_stream[:avg_frame_rate] == '0/0' ? nil : Rational(video_stream[:avg_frame_rate])
-        @r_frame_rate = video_stream[:r_frame_rate] == '0/0' ? nil : Rational(video_stream[:r_frame_rate])
+        @frame_rate  = parse_framerate(video_stream[:avg_frame_rate])
+        @r_frame_rate = parse_framerate(video_stream[:r_frame_rate])
         # For some video streams the frame_rate reported by `ffprobe` will be 0/0, but for these streams we
         # should use `r_frame_rate` instead. Video screencast generated by Gnome Screencast have this issue.
         @frame_rate ||= @r_frame_rate
@@ -55,4 +55,10 @@ class VideoMetadataExtractor
 
     @invalid = true if @metadata.key?(:error)
   end
+
+  def parse_framerate(raw)
+    Rational(raw)
+  rescue ZeroDivisionError
+    nil
+  end
 end