Watson [speech to text]: raw audio does not work through websockets but works through http interface

Question

I have a raw audio file that I would like to transcript using watson speech to text service. I am using the default example provided at the repo.

But it works if I use http interface.

// working code
package main

import (
    "os"

    "github.com/IBM/go-sdk-core/v5/core"
    "github.com/watson-developer-cloud/go-sdk/v2/speechtotextv1"
)

func main() {
    // Instantiate the Watson Speech To Text service
    authenticator := &core.IamAuthenticator{
        ApiKey: "YOUR API KEY",
    }
    service, serviceErr := speechtotextv1.
        NewSpeechToTextV1(&speechtotextv1.SpeechToTextV1Options{
            URL:           "YOUR SERVICE URL",
            Authenticator: authenticator,
        })

    // Check successful instantiation
    if serviceErr != nil {
        panic(serviceErr)
    }

    // Open file with mp3 to recognize
    audio, audioErr := os.Open("/opt/audioRaw.raw")
    if audioErr != nil {
        panic(audioErr)
    }

    // Create a new RecognizeOptions for ContentType "audio/mp3"
    recognizeOptions := service.
        NewRecognizeOptions(audio).
        SetContentType("audio/mulaw;rate=8000;channels=1").SetModel("en-US_NarrowbandModel")

    // Call the speechToText Recognize method
    recognizeResult, _, responseErr := service.Recognize(recognizeOptions)

    // Check successful call
    if responseErr != nil {
        panic(responseErr)
    }

    // Check successful casting
    if recognizeResult != nil {
        core.PrettyPrint(recognizeResult, "Recognize")
    }
}

But if i use websocket for the raw audio file, it does not work and panic with below error upon debugging.

 "error": "unable to transcode data stream application/octet-stream -> audio/l16 "

// Does not work

package main

import (
    "encoding/json"
    "fmt"
    "os"

    "github.com/IBM/go-sdk-core/v5/core"
    "github.com/watson-developer-cloud/go-sdk/v2/speechtotextv1"
)

func main() {
    // Instantiate the Watson Speech To Text service
    authenticator := &core.IamAuthenticator{
        ApiKey: "YOUR API KEY",
    }
    service, serviceErr := speechtotextv1.
        NewSpeechToTextV1(&speechtotextv1.SpeechToTextV1Options{
            URL:           "YOUR SERVICE URL",
            Authenticator: authenticator,
        })

    // Check successful instantiation
    if serviceErr != nil {
        panic(serviceErr)
    }

    // Open file with mp3 to recognize
    audio, audioErr := os.Open("/opt/audioRaw.raw")
    if audioErr != nil {
        panic(audioErr)
    }
    // callbook can have `OnOpen`, `onData`, `OnClose` and `onError` functions
    callback := myCallBack{}

    recognizeUsingWebsocketOptions := service.
        NewRecognizeUsingWebsocketOptions(audio, "audio/mulaw;rate=8000;channels=1")

    recognizeUsingWebsocketOptions.
        SetModel("en-US_NarrowbandModel").
        SetWordConfidence(true).
        SetSpeakerLabels(true).
        SetTimestamps(true)

    service.RecognizeUsingWebsocket(recognizeUsingWebsocketOptions, callback)
}

type myCallBack struct{}

func (cb myCallBack) OnOpen() {
    fmt.Println("Handshake successful")
}

func (cb myCallBack) OnClose() {
    fmt.Println("Closing connection")
}

func (cb myCallBack) OnData(resp *core.DetailedResponse) {
    var speechResults speechtotextv1.SpeechRecognitionResults
    result := resp.GetResult().([]byte)
    json.Unmarshal(result, &speechResults)
    core.PrettyPrint(speechResults, "Recognized audio: ")
}

func (cb myCallBack) OnError(err error) {
    panic(err)
}

Could someone please help me in figure out why raw audio does not work through websocket interface?

Any pointer is much appreciated.

Ryan