Applies to partners who maintain their own S3 buckets for hosting videos.
See and https://foliovision.com/player/fix-amazon-mime-type
For videos hosted on "other sites", video metadata must set the mime-type correctly for the video to play in IE 9/10.
For S3, you edit the metadata for the video files to set the HTTP Header of Content-Type to a Header Value of video/mp4.
Upshot is, be sure to test!