As suggested, my ipod nano (4th generation) won't play any videos. The transfer was fine and I there was no need for me to convert any of the videos into a specific format. My video files are appearing on my ipod however, when clicked will not play. All I get is a black screen. Apparently it's a common problem but its driving me insane. I've already tried restoring my ipod, deleting the files and putting them back on, as well as making use of the 'repair' function when installing itunes again, which has proven to cause more hassle than anything else. Any ideas anyone?
I haven't dealed with the 4th generation, but normally I use Macvide iPod converter (or VideoMobile Converter for Windows). You can try these apps, if your problem is the video format, of cource.