What is the Synchronization Source (SSRC)?

In a Real-time Transport Protocol (RTP) session, the Synchronization Source (SSRC) assists in determining the source endpoint, typically when an endpoint sends multiple media streams that need to be synchronized (e.g., audio and video lip-sync). SSRC identifies the synchronization source (simply called the source). This identifier is chosen randomly and is intended to be unique among all sources of the same RTP session. If a source changes its source transport address, it must also choose a new SSRC identifier.