9.4.1 Dictionary RTCRtpParameters Members
encodings of type sequence<RTCRtpEncodingParameters>
The "encodings" or "layers" to be used for things like simulcast, Scalable Video Coding, RTX, FEC, etc. When unset, send() behaves as described in Section 5.3.3, and receive() as described in Section 6.3.3.

5.3.3 Methods
send
Media to be sent is controlled by parameters. If send() is called with invalid parameters, throw an InvalidParameters exception. If rtcpTransport is not set and send(parameters) is called with parameters.rtcp.mux set to "false", throw an InvalidParameters exception. For each value of i from 0 to the number of codecs, check that each value of parameters.codecs[i].name not equal to "red", "rtx" or a forward error correction codec is included in