      - parameter learningOptOut: If `true`, then this request will not be logged for training.
      - parameter compress: Should microphone audio be compressed to Opus format?
        (Opus compression reduces latency and bandwidth.)
+     - parameter headers: A dictionary of request headers to be sent with this request.
      - parameter failure: A function executed whenever an error occurs.
      - parameter success: A function executed with all transcription results whenever
        a final or interim transcription is received.


        // set headers
        session.defaultHeaders = defaultHeaders

        // set callbacks
        session.onResults = success


        // set headers
        session.defaultHeaders = defaultHeaders
        if let headers = headers {
            session.defaultHeaders.merge(headers) { (_, new) in new }
        }

        // set callbacks
        session.onResults = success
