Hi, welcome to the Magix forums.

First, please read this post and give us ALL the information requested there. At the moment we know nothing about your computer nor even exactly which program, variant and version, you are running!

Second, mp4 is a "container" format; the actual file and the codecs used to create it and to play it, can be extremely varied. So we need much more information about the actual file. Please find, download and install the free MediaInfo utility, point it to you mp4 file and post the results of the Tree view here. That should give us a much better idea of what codecs the file needs in order to allow you to play it.

Jeff
Forum Moderator