docs: def find_video_file(rtdc_dataset):
          """Tries to find a video file that belongs to an RTDC dataset
  
          Returns None if no video file is found.
          """
          video = None
          if rtdc_dataset._fdir.exists():
              # Cell images (video)
              videos = [v.name for v in rtdc_dataset._fdir.rglob("*.avi")]
              # Filter videos according to measurement number
              meas_id = rtdc_dataset._mid
              videos = [v for v in videos if v.split("_")[0] == meas_id]
              videos.sort()
              if len(videos) != 0:
                  # Defaults to first avi file
                  video = videos[0]
                  # g/q video file names. q comes first.
                  for v in videos:
                      if v.endswith("imag.avi"):
                          video = v
                          break
                      # add this here, because fRT-DC measurements also contain
                      # videos ..._proc.avi
                      elif v.endswith("imaq.avi"):
                          video = v
                          break
          if video is None:
              return None
          else:
              return rtdc_dataset._fdir / video