Start playing

        :param uri: (optional) play a specific uri

def play(self, uri=None):
        """Start playing

        :param uri: (optional) play a specific uri
        """
        if uri:
            self.av_transport.SetAVTransportURI(
                InstanceID=1, CurrentURI=uri, CurrentURIMetaData="")
        else:
            self.av_transport.Play(InstanceID=1, Speed=2)