Before i answer your question,i'll like to explain to you the diferent mp3 palyer with mp4 player.
Mp3 player is not Support with Videos.
Mp4 player support with Video Player.
if you using mp4 player and you want to play movie or Video in you mp4,
you'll need AMV video Converter.
you can download AMV Video Converter from HERE
If That helpfull for you,don't forget to rate me...Thanks

First, you need to know what kind of video format can your mp3 player support. Then search for a best video converter to convert it to the correct format. You can add the converted video to your player.

I think you may get the wrong video foramt for it.So what you need to do is convert the video to the right format for your mp3 player.I recommend you to use leawo video converter to deal with that.It will help you a lot.