Slow playback of MP4 files

Posted by Westygeoff
I have recently bought a P910, and travel a lot, so thought I would convert a DVD to MP4 format to watch on the plane, which I did successfully, and it played fine on my computer. However, when I load it onto my phone the playback is v..e..r..y slow. What have I done wrong, and what can I do to improve. I am using ImTOO DVD to create the file.