How much traffic are you expecting to push out per day? A 100mbps port would be needed, and you will most likely want a place where you can buy per TB of bandwidth so you can setup 10TB or 20TB and then setup another server with the same setup, as I'm sure you're not constantly pushing the same amount of traffic and mostly have highs and lows, so it won't be cost efficient to be on a dedicated 100mbps line.
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500 visitors a day, but how many visitors at the same time?
What would be the bitrate of the audio files? what about the video files?
Some more information is required before anyone can give you a good advice. You 'probably' require a dedicated 100 mbit unmetered (or more) , but it depends a lot on the simultanuous visitors and bitrate of the streaming media files.
You need at least 50Mbps->100Mbps dedicated port with quality bandwidth to stream movies. Shared bandwidth is not good for video streaming.
Quad Core CPU, 4GB RAM, and SATA HDD should be good to start.
Take a look at http://vinax.net , their server should be perfect for streaming purpose. I know one of my friends is using their service and very happy.