If MP4 videos don't display when your Articulate content is hosted on a server, it's likely that the server isn't configured to play MP4 files.
Some servers don't have an associated MIME type to support MP4 files. To correct it, do the following on your server:
Your MP4 videos should now play when viewed from the server. If you use a hosting company to host your files, it's best to check with them about adding MP4 as a supported MIME type.