What WebRTC constraints and options should i pass to get interoperability between Firefox and Google chrome

Question

I'm building a chat application for a LAN. I use WebRTC but can't get Firefox and Google chrome to interoperate. I don't know the exact parameters i should pass to RTCPeerConnection createOffer/createAnswer.

I made the tests below with Firefox 31 and Google Chrome 36 in the same computer Fedora Linux 20

RTCPeerConnection is created like: pc = new RTCPeerConnection(null, RTC_PC_OPTIONS);

answers/offers are created like: pc.createOffer(onsuccess, onfail, CONSTRAINTS);

My question is: which parameters (RTC_PC_OPTIONS and CONSTRAINTS) should i pass to get interoperability between the two browsers?

Test 1

RTC_PC_OPTIONS = undefined
CONSTRAINTS = undefined

                        FFx2FFx     FFx2Chrome      Chrome2FFx      Chrome2Chrome
                        -------     ----------      ----------      -------------
dataChannel setup       ok          ok              ok              ok
dataChannel send/recv   ok          ok              ok              ok
Video stream            ok          ok              err [1]         ok

Test 2

MDN recomands this value for RTC_PC_OPTIONS

RTC_PC_OPTIONS = {
    optional: [
        {DtlsSrtpKeyAgreement: true},
        {RtpDataChannels: true}
    ]
};
CONSTRAINTS = undefined

                        FFx2FFx     FFx2Chrome      Chrome2FFx      Chrome2Chrome
                        -------     ----------      ----------      -------------
dataChannel setup       ok          err [2]         err [3]         ok
dataChannel send/recv   ok          -               -               ok
Video stream            ok          -               -               err [4]
                                    ^~~~~~~~~~~~~~~~^ 
                                            ^
                   i used datachannel to do signaling for the video TRCPeerConnection,
                   that is why these were not tested

Test 3

RTC_PC_OPTIONS = undefined
CONSTRAINTS = { 'mandatory': { 'OfferToReceiveAudio': true, 'OfferToReceiveVideo': true } }

                        FFx2FFx     FFx2Chrome      Chrome2FFx      Chrome2Chrome
                        -------     ----------      ----------      -------------
dataChannel setup       ok          ok              ok              err [5]
dataChannel send/recv   ok          ok              ok              -
Video stream            err [6]     ok              err [6]         -

---

1. Chrome creates offer and sends it to FFx, FFx receives offer, creates answer and sends it to chrome,

chrome receives the answer. But onaddstream is not triggred in firefox

---

2. After chrome receives the offer sent by FFx, it logs an error to the console:

Failed to set remote offer sdp: Session error code: ERROR_CONTENT. Session error description: Failed to set data send codecs..

---

3. Chrome sends the offer, FFx sends the answer,

chrome gets this error: Failed to parse SessionDescription. m=application 35224 RTP/SAVPF Expects at least 4 fields.

FFx gets this error: ICE failed, see about:webrtc for more details

In about:webrtc:

Local candidate Remote candidate ICE State Priority Nominated Selected a.b.c.d:35224/udp(host) a.b.c.d:45895/udp(host) frozen 9115005270282354000

---

4. Chrome_1 gets the error: Uncaught NetworkError: Failed to execute 'send' on 'RTCDataChannel': Could not send data

chrome_2 gets the error:

Uncaught SyntaxError: Failed to execute 'addIceCandidate' on 'RTCPeerConnection': The ICE candidate could not be added.

---

5. The caller sends the offer, the callee gets an error:

Failed to set remote offer sdp: Session error code: ERROR_CONTENT. Session error description: Failed to set data send codecs.

---

6. Like [1] everything ok but onaddstream not triggered

Answer 1

So, a few things:

1. Whatever MDN page suggests RTPDataChannels is very outdated (let me know the URL). Both Firefox and Chrome support spec DataChannels now. Same for DTLSSRTPKeyAgreement I believe
2. Make sure you call createDataChannel() before createOffer()
3. Is it video-only, or video+audio? We fixed a bug with video-only streams recently if I recall not triggering onAddStream. That would explain 1 and [6] I think. See bug 1035067, which is landed in Nightly and Aurora (FF33); I've asked for uplift to Beta/32
4. The "expects 4 fields" issue if I recall was bug in Firefox - what versions are you running? We did have a bug fixed in 30(?) where we had an unneeded space on the end which caused chrome to reject it - they patched to avoid it, and we fixed it.

Try it with FF Beta, and Nightly (http://nightly.mozilla.org/). And when you report things like this, please indicate what versions of browser you're using! :-)