I can confirm that I followed up directly with our media platform team on this. We’re unable to open this in QT or VLC, so we believe there is an issue of some kind with the format of your MP4 file (could be e.g. bad metadata, corruption, missing samples, etc…). If you can resolve that such that a standard player like Quicktime will work with it, it is more likely to work with the player in the Twitter app, and thus with the media API.