From Shijun Sun:

1. What happens if a DTMFSender object sender is constructed from an RTCRtpSender object sendObject and methods such as insertDTMF() are called, but sendObject.send() was not previously called to set up the DTMF codec?

var sendObject = new RTCRtpSender(audioTrack, dtlsTransport);
var sender = new RTCDtmfSender(sendObject);
if (sender.canInsertDTMF) {
var duration = 500;
sender.insertDTMF("1234", duration);
} else
log("DTMF function not available");

In the above example (assuming the DTMF function is available) does sender.insertDTMF() throw an InvalidState exception?

1. In the single sender example above, what happens to the audioTrack when DTMF is being sent? Presumably the audioTrack is not encoded, correct? Then once the DTMF tones are played out, audioTrack is encoded and sent over the wire within RTP packets again?