That's not a big problem, I can tell you whole scenario and then you can choose which way to go.
for preventing users to download the videos, you need to setup a streaming server, that will send the chunks of video rather than a whole down to client's player, this can be done either by using Apple's HLS or MPEG-DASH stream (DASH is a new entrant), so any capable media server that can serve both streams can be used - together with player that can support either streams.
for streaming server, there are two options, one's Wowza streaming server, that will cost $65 a month plus additional hardware (dedicated server) to run it, and then there is Softvelum Nimble Streamer (my recommendation) that media server is free, you can optionally pay for the administration panel which costs $20 a month and supports 5 servers and is as well very light (https://wmspanel.com/nimble)
