code: public RTPFormats negotiateAudio(SessionDescription sdp, RTPFormats formats) {
      	this.audio.clean();
      	MediaDescriptorField descriptor = sdp.getAudioDescriptor();
      	descriptor.getFormats().intersection(formats, this.audio);
      	return this.audio;
      }
docs: Negotiates the audio formats to be used in the call.
  @param sdp The session description
  @param formats The available formats
  @return The supported formats. If no formats are supported the returned list will be empty.