fcs_call_answering_issue.js

//As you can see in the video, the issue happens because this.answer returns from an if condition in here:

         // callManager.js
         this.answer = function(callid, onSuccess, onFailure, isVideoEnabled, videoQuality){
            var internalCall = calls[callid],
            videoNegotationAvailable = this.isVideoNegotationAvailable(callid);

           if(internalCall) {
            // check if term side tries to answer an audio only call with video
              if (videoNegotationAvailable === false && isVideoEnabled === true) {
                logger.error("[callManager.answer] Video Session Not Available Error ");
                onFailure(fcs.Errors.VIDEO_SESSION_NOT_AVAILABLE);
                return;
            }
          .......
        }

// Here the culprit is the call to this.isVideoNegotationAvailable(callid) which returns false

   // callManager.js
    this.isVideoNegotationAvailable = function(callid) {
        var internalCall = calls[callid];
        return rtc.isVideoNegotationAvailable(internalCall.sdp);
    };

This calls the isVideoNegotationAvailable  in webtrc.js:

    // webrtc.js
    this.isVideoNegotationAvailable = function(sdp) {
        if (sdp === null || sdp === undefined){
            return false;
        }
        return isSdpHas(sdp, video);
    };

The call to isSdpHas(sdp, video) returns false

Here is the definition of  isSdpHas:

   // webrtc.js
    this.isSdpHas = function(pSdp, type) {
        var msg = "isSdpHas for type " + type + ": ", result = false;

        if (pSdp.indexOf(CONSTANTS.SDP.M_LINE + type) !== -1) {
            result = true;
            logger.info(msg + result);
            return result;
        }

        logger.info(msg + result);
        return result;
    };