尝试在没有有效mediaplayer的情况下调用getduration

I use the code below to play an MP4 video (H.264, AAC codecs) from a URL (The url is perfectly fine, no redirect, 404 or anything). However, I keep getting the errors "attempt to call getduration without a valid mediaplayer" or ERROR/MediaPlayer(382): error (1, -2147483648). Does anyone have any idea how to fix it? ThanksI use the code below to play an MP4 video (H.26