how to prevent downloading video from amazon cloudfront using signed urls

I am amazon cloudfront distribution for video files in my website. To read those files I am using signed url method with canned policy to read video file from amazon cloudfront distribution. Below is the example of signed url.

http://cloudfront-domainname/VideoFileName.mp4?Expires=1427805933&Signature=signature-of-policy-statement&Key-Pair-Id=cloudfront-key-pair-id

If I directly paste this url in address bar, I am able to download the video. How to prevent user from downloading this video but video should play in the HTML5 media player.