RTCRtpStreamStats: firCount property

An integer value indicating how many FIR packets have been received by the sender during the current connection. This value is available only on receivers for video tracks.

The receiver sends a FIR packet to the sender any time it falls behind or loses packets and cannot decode the incoming stream any longer because of the lost data. This tells the sender to send a full frame instead of a delta frame, so that the receiver can catch up.

The higher firCount is, the more often frames were dropped, which may be an indication that the media's bit rate is too high for the available bandwidth, or that the receiving device is overburdened and is therefore unable to process the incoming data.