Things I'd try
> Reupload it and see if it gets fixed
> Re-encode with a different setting (trim the video differently by 1 frame or something) and reupload
> Add borders to make it 16:9 by default. So add 53 black pixels left and 53 black pixels right.
Language: Avisynth
avisource("your video.avi")
addborders(53,0,53,0)
#pointresize(last.width*3,last.height*3) # would make it 720p if you want
EDIT: Probably, instead of adding borders it is a better idea to lay the video on a 16:9 blankclip. That should prevent any unwanted stretching and if you use the script below, it will make your video 720p in the process.
Language: Avisynth
vid = avisource("your video.avi")
vid.pointresize(vid.width*3, vid.height*3)
overlay(blankclip(vid, width=1280, height=720),last, x=159)
If you try, please tell me if it works.
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I had a different problem yesterday. I uploaded an MP4 of 13 minutes length and when I opened the page it would tell 13 minutes but immediately change to 6 minutes and only show half the video. I fixed it by encoding differently (different --crf in x264).
