RTCPeerConnection.createOffer()
The createOffer()
method
of the RTCPeerConnection
interface
initiates the creation of an SDP offer
for the purpose of starting a new WebRTC connection to a remote peer.
The SDP offer includes information
about any MediaStreamTrack
objects
already attached to the WebRTC session, codec, and options supported by the browser,
and any candidates already gathered by the ICE agent,
for the purpose of being sent over the signaling channel
to a potential peer
to request a connection
or to update the configuration of an existing connection.
The return value is a Promise
which, when the offer has been created, is
resolved with a RTCSessionDescription
object containing the newly-created
offer.
Syntax
aPromise = myPeerConnection.createOffer([options]);
myPeerConnection.createOffer(successCallback, failureCallback, [options])
Parameters
options
Optional-
An object providing the following options requested for the offer:
iceRestart
Optional-
To restart ICE on an active connection, set this to
true
. This will cause the returned offer to have different credentials than those already in place. If you then apply the returned offer, ICE will restart. Specifyfalse
to keep the same credentials and therefore not restart ICE. The default isfalse
. offerToReceiveAudio
Optional-
Provides additional control over the directionality of audio. For example, it can be used to ensure that audio can be received, regardless if audio is sent or not.
offerToReceiveVideo
Optional-
Provides additional control over the directionality of video. For example, it can be used to ensure that video can be received, regardless if video is sent or not.
Deprecated parameters
In older code and documentation, you may see a callback-based version of this function.
This has been deprecated and its use is strongly discouraged. You
should update any existing code to use the Promise
-based version of
createOffer()
instead. The parameters for this form of
createOffer()
are described below, to aid in updating existing code.
successCallback
-
A callback function which will be passed a single
RTCSessionDescription
object describing the newly-created offer. errorCallback
-
A callback function which will be passed a single
DOMException
object explaining why the request to create an offer failed. options
Optional-
An optional object providing options requested for the offer.
Return value
A Promise
whose fulfillment handler will receive an object conforming to
the RTCSessionDescriptionInit dictionary which contains the SDP
describing the generated offer. That received offer should be delivered through the
signaling server to a remote peer.
Exceptions
These exceptions are returned by rejecting the returned promise. Your rejection handler should examine the received exception to determine which occurred.
InvalidStateError
DOMException
-
Returned if the
RTCPeerConnection
is closed. NotReadableError
DOMException
-
Returned if no certificate or set of certificates was provided for securing the connection, and
createOffer()
was unable to create a new one. Since all WebRTC connections are required to be secured, that results in an error. OperationError
DOMException
-
Returned if examining the state of the system to determine resource availability in order to generate the offer failed for some reason.
Example
Here we see a handler for the negotiationneeded
event which creates the
offer and sends it to the remote system over a signaling channel.
Note: Keep in mind that this is part of the signaling process, the
transport layer for which is an implementation detail that's entirely up to you. In
this case, a WebSocket connection is
used to send a JSON message with a type
field with the
value "video-offer" to the other peer. The contents of the object being passed to the
sendToServer()
function, along with everything else in the promise
fulfillment handler, depend entirely on your design.
myPeerConnection.createOffer().then(function(offer) {
return myPeerConnection.setLocalDescription(offer);
})
.then(function() {
sendToServer({
name: myUsername,
target: targetUsername,
type: "video-offer",
sdp: myPeerConnection.localDescription
});
})
.catch(function(reason) {
// An error occurred, so handle the failure to connect
});
In this code, the offer is created, and once successful, the local end of the
RTCPeerConnection
is configured to match by passing the offer (which is
represented using an object conforming to RTCSessionDescriptionInit) into
setLocalDescription()
. Once
that's done, the offer is sent to the remote system over the signaling channel; in this
case, by using a custom function called sendToServer()
. The implementation
of the signaling server is independent from the WebRTC specification, so it doesn't
matter how the offer is sent as long as both the caller and potential receiver are using
the same one.
Use Promise.catch()
to trap and handle errors.
See Signaling and video calling for the complete example from which this snippet is derived; this will help you to understand how the signaling code here works.
Specifications
Specification |
---|
WebRTC 1.0: Real-Time Communication Between Browsers # dom-rtcpeerconnection-createoffer |
Browser compatibility
BCD tables only load in the browser