RTCRtpScriptTransform: RTCRtpScriptTransform() constructor

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

The RTCRtpScriptTransform() constructor creates a new RTCRtpScriptTransform object.

Constructing the RTCRtpScriptTransform creates a counterpart RTCRtpScriptTransformer in the specified worker, along with passed options (if any). Objects in the third parameter to the constructor are transferred.

The rtctransform event is then fired at the worker global object. Worker code can use the event.transformer property to get the counterpart RTCRtpScriptTransformer, and event.transformer.options is used to get the options.

Note that the options are primarily used to inform the worker whether the transformer is processing incoming or outgoing frames, so that it can apply an appropriate transform.


new RTCRtpScriptTransform(worker)
new RTCRtpScriptTransform(worker, options)
new RTCRtpScriptTransform(worker, options, transfer)



A Worker, which will define code for one or more WebRTC transform streams.

options Optional

An arbitrary object that will be made available in the worker. This is most commonly used to inform the worker whether it injected into the WebRTC sender or receiver pipeline, and hence which transform should be applied. However it may also be used to send any other object, such as a MessagePort for communicating dynamically with the transformer.

transfer Optional

An optional array of transferable objects that will be transferred to the worker. After transfer, these objects are unusable in the main thread.


DataCloneError DOMException

Thrown if an object in transfer cannot be transferred.


The first example below shows construction of a RTCRtpScriptTransform that is then assigned to a RTCRtpSender.transform. The constructor takes an optional object with the property name and senderTransform. The worker can use this option to understand when it is transforming encoded frames from the encoder (rather than incoming frames from the packetizer).

// Create a worker containing a TransformStream
const worker = new Worker("worker.js");
videoSender.transform = new RTCRtpScriptTransform(worker, {
  name: "senderTransform",

Any property name and value can be used in the options, as long as they can be serialized (and transferred if specified in the last constructor parameter). The code below transfers the second port of a MessageChannel to the worker, which we might do in order to dynamically update transform code with (say) a new encryption key.

// Create a worker containing a TransformStream
const worker = new Worker("worker.js");
const channel = new MessageChannel();

const transform = new RTCRtpScriptTransform(
  { purpose: "encrypt", port: channel.port2 },


WebRTC Encoded Transform
# dom-rtcrtpscripttransform-rtcrtpscripttransform

Browser compatibility

BCD tables only load in the browser

See also