Issue with downloading youtube videos with swift -

i trying download youtube video in app , used this , library included in answer app crashing error :

fatal error: unexpectedly found nil while unwrapping optional value

here swift code:

import uikit  class viewcontroller: uiviewcontroller {      let videoid = "hs5cfp8n_js"     var extractor = lbyoutubeextractor()      override func viewdidload() {         super.viewdidload()      }     @ibaction func start(sender: anyobject) {          var url: string = "https://www.youtube.com/watch?v=hs5cfp8n_js"         let testurl = nsurl(string:url)         if testurl != nil {             extractor = lbyoutubeextractor(url: testurl, quality: lbyoutubevideoqualitylarge)             extractor.extractvideourlwithcompletionblock({(videourl, error) in                 if error == nil {                     println(videourl)                     dispatch_async(dispatch_get_global_queue(dispatch_queue_priority_default, 0), {                          let data = nsdata(contentsofurl: videourl)!                         let pathtodocs = nssearchpathfordirectoriesindomains(.documentdirectory, .userdomainmask, true)[0] as! string                         let filename = "video_\(self.videoid).mp4"                         let yourpath = pathtodocs.stringbyappendingpathcomponent(filename)                         data.writetofile(yourpath, atomically: true)                         println("file \(filename) saved")                     })                 } else {                     println("failed extracting video url using block due error:\(error)")                 }              })         }     } } 

my project crashing @ line:

let data = nsdata(contentsofurl: videourl)! 

but can videourl in console:

http%3a%2f%2fr3---sn-tv0cgv5qc5oq-nu8e.googlevideo.com%2fvideoplayback%3fsver%3d3%26id%3d852e427cff27fe3b%26dur%3d55.681 ... ty=small

i don't know missing.

here sample project.