ANDROID：如何将视频文件下载到SD卡？

I have a video file on a website in .MP4 format and I want to allow the user to be able to download the video to their SD card by clicking a link. Is there an easy way to do this. I currently have this code but its not working...not sure what I am doing wrong. THanks for any help!I have a video file on a website in .MP4 format