Q: Problems with iPod iTouch Sync

See:

iTunes: May be unable to transfer videos to iPhone, iPad, or iPod

iTunes: Frequently asked questions about viewing and syncing videos

You may need a computer app like the free HandBrake to convert the format to one compatible with the iPod.

If you do not have a 4G iPod and you purchased the media from iTunes you may have to redownload the SD version since only the 4G can play HD.

Downloading past purchases from the App Store, iBookstore, and iTunes Store