When you include a link to a local mp4 movie, in5 also searches in the same folder for webm and ogv movies with the same name (in order to support additional browsers) and includes them in the output.
If you include one or both of those file formats, the media play should play the format that works with the browser.
You can also add MIME types to your server to play additional formats. The server shouldn't be the limitation when it comes to playing video (unless the server is incorrectly configured). The limitation should be what the user's browser is able to play.
