Hi - YES! I searched Google and discovered something. In Amazon S3, for IE9 to know what kind of file your video is you have to specify the Content Type because apparently IE9 can't figure it out for itself. In S3, highlight the video file, go to Properties, Metadata. There you will see:
Key: Content Type
Change the Value from "application/octet-stream" to "video/mp4", you will have to manually type it there. Save it and that's it - IE9 works. I spent way too many hours on this one..
Here is what I found on Google:
FYI - the author of this plugin seems to respond to questions here:
There is a link to that on the main site, http://mediaelementjs.com/ after you go to the Support page.