Hi, welcome to the Magix forums.

First, please read this post and give us a lot more information, especially about your computer, the version of VPX you are running, the precise info about the mp4 file you are importing (mp4 is a container format, the actual file could be in a variety of different formats - search for the free MediaInfo utility and post here the results of what it says about the content of your original file - ) and the exact Export settings you are using for the new file you are creating.

With this information we are likely to be able to offer some suggestions to you!

Jeff
Forum Moderator