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.

RTCEncodedAudioFrame.timestamp Read only

Returns the timestamp at which sampling of the frame started.

RTCEncodedAudioFrame.data

Return a buffer containing the encoded frame data.

RTCEncodedAudioFrame.getMetadata()

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;
      controller.enqueue(encodedFrame);
    },
  });
  event.transformer.readable
    .pipeThrough(transform)
    .pipeTo(event.transformer.writable);
});

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

• Using WebRTC Encoded Transforms
• TransformStream
• RTCRtpScriptTransformer
• RTCEncodedVideoFrame