.MP4 is just the container. In there is the codec you use.
Normally it will be H.264.
“undf” just means “undefined”.
That means, it is just an unknown codec or the file is damaged.
First check to reproduce the film ones more, to make sure, the file is not just damaged … if its not possible try to transform it with a program like: FormatFactory
If you do it again, make sure, you use within MP4 the H.264 codec.