Download and Playing online mp3 file is not working properly

I have a mp3 file saved on a http server. I have to download and play it runtime. But I encountered a strange problem: the length of AudioCilp is shorter than the origin file.

My mp3 file is served at http://file.gongfubb.com/test/1.mp3.

My code is shown below:

 IEnumerator DownloadClips()
     {
         using (UnityWebRequest www = UnityWebRequestMultimedia.GetAudioClip("http://file.gongfubb.com/test/1.mp3", AudioType.MPEG))
         {
             yield return www.SendWebRequest();
 
             if (www.isNetworkError || www.isHttpError)
             {
                 Debug.LogError(www.error);
             }
             else
             {
                 AudioClip myClip = DownloadHandlerAudioClip.GetContent(www);
 
                 Debug.Log(myClip.length);
             }
         }
     }

The output is 5.256s, but actually the length of the mp3 file is 6.480s. In the fect, I can't get the end of the audio.

My unity version is 2019.3.f1. Any replay would be much appreciated.