Limited availability

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

Note: This feature is available in Dedicated Web Workers.

The RTCEncodedAudioFrame of the WebRTC API represents an encoded audio frame in the WebRTC receiver or sender pipeline, which may be modified using a WebRTC Encoded Transform.

The interface provides methods and properties to get metadata about the frame, allowing its format and order in the sequence of frames to be determined. The data property gives access to the encoded frame data as a buffer, which might be encrypted, or otherwise modified by a transform.

Note: This feature is available in Dedicated Web Workers.

Instance properties

RTCEncodedAudioFrame.timestamp Read only

Returns the timestamp at which sampling of the frame started.


Return a buffer containing the encoded frame data.

Instance methods


Returns the metadata associated with the frame.


This code snippet shows a handler for the rtctransform event in a Worker that implements a TransformStream, and pipes encoded frames through it from the event.transformer.readable to event.transformer.writable (event.transformer is a RTCRtpScriptTransformer, the worker-side counterpart of RTCRtpScriptTransform).

If the tranformer is inserted into an audio stream, the transform() method is called with a RTCEncodedAudioFrame whenever a new frame is enqueued on event.transformer.readable. The transform() method shows how this might be read, modified using a fictional encryption function, and then enqueued on the controller (this ultimately pipes it through to the event.transformer.writable, and then back into the WebRTC pipline).

addEventListener("rtctransform", (event) => {
  const async transform = new TransformStream({
    async transform(encodedFrame, controller) {
      // Reconstruct the original frame.
      const view = new DataView(encodedFrame.data);

      // Construct a new buffer
      const newData = new ArrayBuffer(encodedFrame.data.byteLength);
      const newView = new DataView(newData);

      //Encrypt frame bytes using the encryptFunction() method (not shown)
      for (let i = 0; i < encodedFrame.data.byteLength; ++i) {
        const encryptedByte = encryptFunction(~view.getInt8(i));
        newView.setInt8(i, encryptedByte);

      encodedFrame.data = newData;

Note that more complete examples are provided in Using WebRTC Encoded Transforms.


WebRTC Encoded Transform
# ref-for-rtcencodedaudioframe%E2%91%A1

Browser compatibility

BCD tables only load in the browser

See also