code: def formatter(self, api_client, data, newval):
          
          url_map = data.get("audioUrlMap")
          audio_url = data.get("audioUrl")
  
          # Only an audio URL, not a quality map. This happens for most of the
          # mobile client tokens and some of the others now. In this case
          # substitute the empirically determined default values in the format
          # used by the rest of the function so downstream consumers continue to
          # work.
          if audio_url and not url_map:
              url_map = {
                  BaseAPIClient.HIGH_AUDIO_QUALITY: {
                      "audioUrl": audio_url,
                      "bitrate": 64,
                      "encoding": "aacplus",
                  }
              }
          elif not url_map:  # No audio url available (e.g. ad tokens)
              return None
  
          valid_audio_formats = [BaseAPIClient.HIGH_AUDIO_QUALITY,
                                 BaseAPIClient.MED_AUDIO_QUALITY,
                                 BaseAPIClient.LOW_AUDIO_QUALITY]
  
          # Only iterate over sublist, starting at preferred audio quality, or
          # from the beginning of the list if nothing is found. Ensures that the
          # bitrate used will always be the same or lower quality than was
          # specified to prevent audio from skipping for slow connections.
          preferred_quality = api_client.default_audio_quality
          if preferred_quality in valid_audio_formats:
              i = valid_audio_formats.index(preferred_quality)
              valid_audio_formats = valid_audio_formats[i:]
  
          for quality in valid_audio_formats:
              audio_url = url_map.get(quality)
  
              if audio_url:
                  return audio_url[self.field]
  
          return audio_url[self.field] if audio_url else None
docs: Get audio-related fields
  
          Try to find fields for the audio url for specified preferred quality
          level, or next-lowest available quality url otherwise.