Did you know there isn't just one type of digital video format? If you've ever worked with video editing, you know that there are dozens of different ways to encode video.
On top of that, some media players can't play certain formats of video. So when you want to play back or edit a video, you may have to find and download the right codec or program.
Or you could download HandBrake. It is an all-purpose video transcoding program. That means it can convert videos between many common file formats.
There are lots of handy presets that make HandBrake easy to use. It is also capable of ripping home video onto your computer. It can't, however, break commercially encrypted DVDs.