Essentially you need a media playback device which can access the hard drive and has the correct connections to output audio and video to those connections. Assuming this is a USB hard disk, something you probably already own which will do this is a computer - you would just need to buy the necessary output cables e.g. a 3.5mm headphone connection to the RCA phono on your ampilfier cable would do this.
It would help to know a bit more of your setup and your requirements e.g. you say you want to output video, but don't mention anything - is this to a TV and sound setup in your living room, or is this a completely different setup? What amplifier do you have and do you have any other equipment already in place? It will be easier to advise once we have a fuller picture.