The codecId property of the RTCOutboundRtpStreamStats dictionary is a string that uniquely identifies the object that was inspected to produce the data in the RTCCodecStats for the RTP stream.
RTCOutboundRtpStreamStats and RTCCodecStats objects are correlated by iterating the RTCStatsReport to find the statistics objects where RTCOutboundRtpStreamStats.codecId is equal to RTCCodecStats.id.
A string that contains the id of the object that was inspected to produce the RTCCodecStats object associated with this RTP stream.