Using DTMF with WebRTC - Web APIs
browser doesn't support rtcpeerconnection.addtrack().
... "back to the <strong>deprecated</strong> addstream() method..."); callerpc.addstream(stream); } if (callerpc.getsenders) { dtmfsender = callerpc.getsenders()[0].dtmf; } else { log("your browser doesn't support rtcpeerconnection.getsenders(), so " + "falling back to use <strong>deprecated</strong> createdtmfsender() " + "instead."); dtmfsender = callerpc.createdtmfsender(audiotracks[0]); } dtmfsender.ontonechange = handletonechangeevent; } after setting audiotracks to be a list of the audio tracks on the stream from the user's microphone, it's time to add the media to the caller's rtcpeerconnection.
...entry in the returned list of senders; this is the rtcrtpsender responsible for transmitting data for the first audio track on the call (which is the track we'll send dtmf over).

RTCPeerConnection - Web APIs
at.setremotedescription()the rtcpeerconnection method setremotedescription() sets the specified session description as the remote peer's current offer or answer.