The iPhone is a cool portable device for watching videos, movies and TV shows. If you own a DVD disc, you don't need to download the movie from iTunes Store and pay for it twice in order to view it on your iPhone. You just get the DVD movie converted to the iPhone supported video format and then sync the output to your iPhone.
You must have stored lots of video files in your computer hard drive. If you want to enjoy them on your iPhone, you may find not all of them can be successfully transferred to your iPhone. For the video files in formats such as AVI, FLV, MKV, MTS, M2TS, WMV, you need to convert them to iPhone video files first.