iPhones, iPads and the iPod touch are really great devices for watching video on and you may have purchased some from the iTunes Store, downloaded from other sites or converted some from DVDs. But what about those video you have that are in a format that will not play on your device. It could be an AVI, WMV, Flash video (FLV) or something else.
You need to convert these to a format that will work and these iOS devices like formats called h.264 or MPEG-4. They usually can be identified because they end in MP4, M4V or MOV.
So how do you convert the videos to these formats, well I use Handbrake, it is free and can be downloaded for Windows, Mac and Linux from http://handbrake.fr
Here is a video to show you how to convert these file formats, this video shows converting a Flash video file, an FLV, but works the same for other videos formats.