...vob.asf wmv mp4 ogm? Probably "format" is not the right word. The reason for asking this question is I purchased some instructional DVDs and I want to make a backup copy of all of them because they are very expensive. They dont come with any restriction so it is easy to make a copy. But what I noticed is that they all come with different.......wmv mp4 ogm vob avi....etc Why? I have never studied computer science but I know how to use a computer, so I am not familiar with these extensions ogm avi....etc but I know that if I want them to play back in my portable DVD player I need to convert them to mpeg the avi version will not play. Why? Does the following analogy some what apply..? lets say people want to eat Rice... and there are 20 cooks ready to cook rice for those people but every cook cooks the rice in a different way... but the final product it is just about the same..... Cooked rice.... Please give me some links to learn more about avi vob etc but also give me a rough idea of why this is done in this way. Not very clear my question so I hope I get someone to understand what I am trying to ask. Thanks