code: def return_videos(self, begtime, endtime):
          
          try:
              self._orig['po_videoSyncups']
          except KeyError:
              raise OSError('No po_videoSyncups.xml in folder to sync videos')
  
          if not self._videos:
              raise OSError('No mp4 video files')
  
          mp4_file = self._videos[:1]  # make clear we only use the first video
  
          return mp4_file, begtime, endtime
docs: It returns the videos and beginning and end time of the video
          segment. The MFF video format is not well documented. As far as I can
          see, the manual 20150805 says that there might be multiple .mp4 files
          but I only see one .mov file (and no way to specify which video file to
          read). In addition, there is a file "po_videoSyncups.xml" which seems
          to contain some time information, but the sampleTime does not start at
          zero, but at a large number. I don't know how to use the info in
          po_videoSyncups.xml.
  
          Parameters
          ----------
          begtime : float
              start time of the period of interest
          endtime : float
              end time of the period of interest
  
          Returns
          -------
          list of one path
              list with only one element
          float
              start time of the video
          float
              end time of the video