It depends what player you are using, some players like Flowplayer allow the masking of video urls, this is simply to stop people scrapping your videos and using your bandwidth on their website showing your videos without permission.

Some will change the masking code of the url every few seconds, so if someone did borrow it and steal your bandwidth, then this would be one way to combat it, as the link they copy will change, therefore become broken on any site that borrows it, steals it. (edit to add, they never truly know the real video url, therefore it never becomes at risk, they only know the temporary mask at the moment they steal it, but changes minutes later)

If you are doing video, might want to get a Webm and mp4 versions of the same video, as Chrome only plays Webm format, Firefox plays mp4. You might also want to use a CDN like Amazon S3 and Cloud in conjunction to distribute the video, as lagging will occur most likely unless distributed via CDN, it is also the cheapest option.

There are alternatives like storing an alternative code which is called upon and decoded, but the above method is well known, most players will allow to mask, depending on the player you are using.

Alex