The rid property of the RTCOutboundRtpStreamStats dictionary is a string that specifies the RTP stream ID, if defined.
The property is only defined where the rid has been set for the corresponding RTCRtpSender. If set, this value will be present regardless of whether the RID RTP header extension has been negotiated.
The value of the encodings.rid argument passed to RTCRtpSender.setParameters(), if any, when the corresponding transceiver is created. The property is undefined if the stream ID was not set.
Note: The property is undefined for audio streams.