Q: my movies won't play on my ipod

I just downloaded some movies to play on my ipod touch but they won't play on my ipod for some reason. all of them are mp4 files and h.264 (i don't know what this means but seems to be useful when I searched online to see if I could find answers) format (?). They play on itunes but when I try to sync it with my ipod, they won't copy because supposedly they cannot be played on this ipod. my ipod touch model is the one just before the model with the camera attached came out. (ver 4.2.1 is what it says in the info).