Each SDP media section describes one bidirectional SRTP ("Secure Real Time Protocol") stream (excepting the media section for
RTCDataChannel, if present). This pairing of send and receive SRTP streams is significant for some applications, so
RTCRtpTransceiver is used to represent this pairing, along with other important state from the media section. Each non-disabled SRTP media section is always represented by exactly one transceiver.
A transceiver is uniquely identified using its
mid property, which is the same as the media ID (
mid) of its corresponding m-line. An
RTCRtpTransceiver is associated with an m-line if its
mid is non-null; otherwise it's considered disassociated.