我遇到了 Amazon Lex 的语音输入编码问题。
如果我将 InputStream 分配为空，它会起作用，我会收到来自 Lex 的默认语音回答：“我该如何帮助你”
var amazonLexClient = new AmazonLexClient("APPID", "APPSECRET", Amazon.RegionEndpoint.USEast1);
var amazonPostRequest = new Amazon.Lex.Model.PostContentRequest();
var amazonPostResponse = new Amazon.Lex.Model.PostContentResponse();
amazonPostRequest.BotAlias = "BookTrip";
amazonPostRequest.BotName = "BookTrip";
amazonPostRequest.ContentType = "audio/l16; rate=16000; channels=1";
amazonPostRequest.UserId = "user";
amazonPostRequest.InputStream = null;
amazonPostResponse = await amazonLexClient.PostContentAsync(amazonPostRequest);
如果我尝试使用下面的编码（Lex 要求：16KHz、8 位、1 通道）发送录制的语音“你好吗”
var amazonLexClient = new AmazonLexClient("APPID", "APPSECRET", Amazon.RegionEndpoint.USEast1);
var amazonPostRequest = new Amazon.Lex.Model.PostContentRequest();
var amazonPostResponse = new Amazon.Lex.Model.PostContentResponse();
amazonPostRequest.BotAlias = "BookTrip";
amazonPostRequest.BotName = "BookTrip";
amazonPostRequest.ContentType = "audio/l16; rate=16000; channels=1";
amazonPostRequest.UserId = "user";
amazonPostRequest.InputStream = new MemoryStream();
WaveFormat target = new WaveFormat(16000, 8, 1);
WaveStream streamIn = new WaveFileReader("F:\\Whatever.wav");
WaveFormatConversionStream str = new WaveFormatConversionStream(target, streamIn);
WaveFileWriter.WriteWavFileToStream(amazonPostRequest.InputStream, str);
amazonPostResponse = await amazonLexClient.PostContentAsync(amazonPostRequest);
然后就不行了，大约 20~25s 后 Lex 服务器会返回 null。
Amazon.Runtime.AmazonUnmarshallingException: 'Error unmarshalling response back from AWS.'
NullReferenceException: Object reference not set to an instance of an object.
谁能告诉我如何对 wav 文件进行编码以使其与 Amazon Lex 一起使用？顺便说一句，我使用 Visual Studio 2017、C# 和 NAudio 库。