In my website I stream users mp4 content. I also allow users to download. However in Chrome it seems to automatically play the file in an internal player instead of download
Sounds like you are using a direct href to the mp4. If you are using any server side languages (i.e.asp.net, php, etc) language on your website you can force a download. In asp or .net you can use HttpHandlers with "content-disposition","attachment; filename=fname.ext" or return File() ActionResult in MVC. Let me know if you can use any server side code and I can provide some code.
Alternatively you can try the html5 download attribute: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/a?redirectlocale=en-US&redirectslug=HTML%2FElement%2Fa#attr-download
Or, try javascript/jQuery. Here is a plugin: http://johnculviner.com/jquery-file-download-plugin-for-ajax-like-feature-rich-file-downloads/