在上一章已詳細說明如何讀取本地音訊檔案，呼叫GoogleCloudSpeech API轉換為文字。從中可以看出，對音訊檔案的播放長度嚴格地限制在60s以內。對此限制，Google採用將音訊檔案上傳到Cloud Storage的Bucket中，然後進行文字轉換，大大地增長了檔案的播放長度。針對在Google Cloud PlatForm中的系列操作及上傳檔案到Cloud Storage Bucket中的方式，請檢視GoogleCloudSpeechAPI 的呼叫注意事項 。

讀取Cloud Storage Bucket中的音訊檔案進行文字轉換

注：如下Demo是windows應用程式，所有方法都為static

1.建立型別為CloudSpeechAPIService的方法，目的是通過環境變數獲取Google的憑證，連線在雲平臺建立的專案。PS：如果此方法出現異常，請檢視上一章的前提條件二。

static public CloudSpeechAPIService CreateAuthorizedClient()
    {
        GoogleCredential credential =GoogleCredential.GetApplicationDefaultAsync().Result;//讀取環境變數中的GOOGLE_APPLICATION_CREDENTIALS

        if (credential.IsCreateScopedRequired)
        {
            credential = credential.CreateScoped(new[]
            {
                CloudSpeechAPIService.Scope.CloudPlatform
            });//獲取認證
        }
        return new CloudSpeechAPIService(new BaseClientService.Initializer()
        {
            HttpClientInitializer = credential,
            ApplicationName = "DotNet Google Cloud Platform Speech Sample",
        });
    }
 

2.選擇Cloud Storage Bucket中的音訊檔案，呼叫該API進行文字轉換。ps：音訊檔案格式最好為1聲道PCM，播放時間小於80minutes否則轉換容易出錯。

   private static void SpeechTotextByUri()
        {

            var service = CreateAuthorizedClient();//獲取Google雲認證
            var request = new Google.Apis.CloudSpeechAPI.v1beta1.Data.AsyncRecognizeRequest
 
()
            {
                Config = new Google.Apis.CloudSpeechAPI.v1beta1.Data.RecognitionConfig()
                {
                    Encoding = "LINEAR16",//編碼格式PCM
                    SampleRate = 16000,//取樣頻率16000HZ
                    LanguageCode = "en-US"//英文播放檔案
                    //  LanguageCode = "cmn-Hans-CN"中文播放檔案
                },
                Audio = new Google.Apis.CloudSpeechAPI.v1beta1.Data.RecognitionAudio()
                {
                     Uri= "gs://Storage中的Bucket名稱/該Bucket中的音訊檔案"//如Google提供的 Uri= "gs://cloud-samples-tests/speech/brooklyn.flac"
                }
            };

            DateTime startTime = DateTime.Now;
            Console.WriteLine("Sarte Time ：" + startTime);
            StringBuilder sb = new StringBuilder();
            try
            {
                var asyncResponse = service.Speech.Asyncrecognize(request).Execute();
                var name = asyncResponse.Name;
                Google.Apis.CloudSpeechAPI.v1beta1.Data.Operation op;
                do
                {
                    Console.WriteLine("Waiting for server processing...");
                    Thread.Sleep(1000);
                    op = service.Operations.Get(name).Execute();
                    if (op.Error?.Message != null)
                    {
                        Console.WriteLine(op.Error.Message);
                    }
                } while (!(op.Done.HasValue && op.Done.Value));
                dynamic results = op.Response["results"];

                StringBuilder sbContent = new StringBuilder();
                foreach (var result in results)
                {
                    foreach (var alternative in result.alternatives)
                    {
                        sbContent.Append(alternative.transcript);
                    }
                }
                sb.Append(sbContent);
                Console.WriteLine("The result:");
                Console.WriteLine();
                Console.WriteLine(sbContent.ToString());
                Console.WriteLine();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            DateTime endTime = DateTime.Now;
            var timeTaken = endTime - startTime;
            Console.WriteLine("End Time:" + endTime + "\t" + "Time-taken:" + (timeTaken));
            sb.Append("\r\nEnd Time:" + endTime + "\t" + "Time-taken:" + (timeTaken));
            try
            {
              //將轉換的文字內容儲存到本地
                StreamWriter sw = new StreamWriter(Directory.GetCurrentDirectory() + $"\\{filename}_result.txt");
                sw.Write(sb.ToString());
                sw.Close();
            }
            catch (Exception ex)
            {
                Console.WriteLine("Write file failed!\t" + ex.Message);
            }
            Console.WriteLine();
            Console.WriteLine("Enter any key to exit the program!");
            Console.ReadKey();
        }

PS：使用的名稱空間有：

using System;
using Google.Apis.CloudSpeechAPI.v1beta1;
using Google.Apis.Auth.OAuth2;
using Google.Apis.Services;
using System.IO;
using System.Text;
using System.Threading;
using Google.Cloud.Storage.V1;

結果如下：