var credential = GoogleCredential.GetApplicationDefault();
var client = SpeechClient.Create();
var _longOp = client.LongRunningRecognize(new RecognitionConfig()
{
    Encoding = RecognitionConfig.Types.AudioEncoding.Linear16,
    SampleRateHertz = 8000,
    LanguageCode = languageCode
}, RecognitionAudio.FromStorageUri(audioPath));
_longOp = _longOp.PollUntilCompleted();
var response = _longOp.Result;
foreach (var result in response.Results)
{
    foreach (var alternative in result.Alternatives)
    {
        _transcipt += alternative.Transcript;
    }
}