public class SpeechService
    {
        private static SpeechSynthesizer synth = null;
        /// <summary>
        /// 返回一个SpeechSynthesizer对象
        /// </summary>
        /// <returns></returns>
        private static SpeechSynthesizer GetSpeechSynthesizerInstance()
        {
            if (synth == null)
            {
                synth = new SpeechSynthesizer();
            }
            return synth;
        }
        /// <summary>
        /// 保存语音文件
        /// </summary>
        /// <param name="text"></param>
        public static void SaveMp3(string strFileName,string spText)
        {    
            synth = GetSpeechSynthesizerInstance();
            synth.Rate = 1;
            synth.Volume = 100;      
            synth.SetOutputToWaveFile(strFileName);
            synth.Speak(spText);
            synth.SetOutputToNull();
        }  
    }

  public async Task<ActionResult> PlayWav(string id,string spText)
        {    
            string strPath = Server.MapPath("~\\MP4\\" + id + ".wav");
            SpeechService.SaveMp3(strPath, spText);
            try
            {     
                using (FileStream fileStream = new FileStream(strPath, FileMode.Open))
                {
                    byte[] fileByte = new byte[fileStream.Length];
                    fileStream.Seek(0, SeekOrigin.Begin);
                    fileStream.Read(fileByte, 0, (int)fileStream.Length);
                    long fSize = fileStream.Length;
                    long startbyte = 0;
                    long endbyte = fSize - 1;
                    int statusCode = 200;
                    if ((Request.Headers["Range"] != null))
                    {
                        //Get the actual byte range from the range header string, and set the starting byte.
                        string[] range = Request.Headers["Range"].Split(new char[] { '=', '-' });
                        startbyte = Convert.ToInt64(range[1]);
                        if (range.Length > 2 && range[2] != "") endbyte = Convert.ToInt64(range[2]);
                        //If the start byte is not equal to zero, that means the user is requesting partial content.
                        if (startbyte != 0 || endbyte != fSize - 1 || range.Length > 2 && range[2] == "")
                        { statusCode = 206; }//Set the status code of the response to 206 (Partial Content) and add a content range header.                                    
                    }
                    long desSize = endbyte - startbyte + 1;
                    //Headers
                    Response.StatusCode = statusCode;
                    Response.ContentType = "audio/mpeg";
                    Response.AddHeader("Content-Accept", Response.ContentType);
                    Response.AddHeader("Content-Length", desSize.ToString());
                    Response.AddHeader("Content-Range", string.Format("bytes {0}-{1}/{2}", startbyte, endbyte, fSize));
                    return File(fileByte, Response.ContentType);
               
                }
            }
            catch (Exception ex)
            {
                throw;
            }
        }