Is a DVD machine a computer?

Computers come in many guises. Your quartz wrist watch has a small computer in it, but it is a pre programmed computer - it can only perform a limited set of actions.

Similarly with a DVD player - it will have a dedicated computer in it telling it when to start and when to stop, and what to do when the 'eject' button is pressed.

However, a bigger class of computers are the 'programmable computers' - devices in which their programming may be changed. (within reason).

The machine you are using to access the internet is of this sort. You can program it for letter writing, spreadsheets, displaying photos and so on.

So your DVD machine has a computer in it, but one of quite limited and predetermined function.