Google Cloud Speech API 调用注意事项及调用方式__.Net版2

在上一章已详细说明如何读取本地音频文件，调用GoogleCloudSpeech API转换为文字。从中可以看出，对音频文件的播放长度严格地限制在60s以内。对此限制，Google采用将音频文件上传到Cloud Storage的Bucket中，然后进行文字转换，大大地增长了文件的播放长度。针对在Google Cloud PlatForm中的系列操作及上传文件到Cloud Storage Bucket中的方式，请查看GoogleCloudSpeechAPI 的调用注意事项 。

读取Cloud Storage Bucket中的音频文件进行文字转换

注：如下Demo是windows应用程序，所有方法都为static

1.创建类型为CloudSpeechAPIService的方法，目的是通过环境变量获取Google的凭证，连接在云平台建立的项目。PS：如果此方法出现异常，请查看上一章的前提条件二。

static public CloudSpeechAPIService CreateAuthorizedClient()
    {
        GoogleCredential credential =GoogleCredential.GetApplicationDefaultAsync().Result;//读取环境变量中的GOOGLE_APPLICATION_CREDENTIALS

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

2.选择Cloud Storage Bucket中的音频文件，调用该API进行文字转换。ps：音频文件格式最好为1声道PCM，播放时间小于80minutes否则转换容易出错。

   private static void SpeechTotextByUri()
        {

            var service = CreateAuthorizedClient();//获取Google云认证
            var request = new Google.Apis.CloudSpeechAPI.v1beta1.Data.AsyncRecognizeRequest()
            {
                Config = new Google.Apis.CloudSpeechAPI.v1beta1.Data.RecognitionConfig()
                {
                    Encoding = "LINEAR16",//编码格式PCM
                    SampleRate = 16000,//采样频率16000HZ
                    LanguageCode = "en-US"//英文播放文件
                    //  LanguageCode = "cmn-Hans-CN"中文播放文件
                },
                Audio = new Google.Apis.CloudSpeechAPI.v1beta1.Data.RecognitionAudio()
                {
                     Uri= "gs://Storage中的Bucket名称/该Bucket中的音频文件"//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
            {
              //将转换的文字内容保存到本地
                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：使用的命名空间有：

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;

结果如下：