Fix `frame_rate` for videos where `ffprobe` reports 0/0 (#26500)

app/lib/video_metadata_extractor.rb

@@ -43,6 +43,9 @@ class VideoMetadataExtractor
         @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])
+        # 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
       end
 
       if (audio_stream = audio_streams.first)