     if obj.filename?
       @filename = obj.filename
     else
-      alert 'no filename specified'
+      console.error 'no filename specified'
       return
 
     if !obj.itag?
-      alert 'No format specified'
+      console.error 'No format specified'
       return
 
     @itag = obj.itag
     if !@formats[@itag]?
-      alert 'Wrong format specified'
+      console.error 'Wrong format specified'
       return
 
     @startByte = @timeToBytes(@start)

      startMs = @parseTime(start)
      endMs = @parseTime(end)
      if not stratS<endS
        alert 'Range is invalid'
        return
      [startMs,endMs]


      if temp.status!='ok'
        console.log 'error',temp.reason
        return

      @formats = {}
      for itag,i in temp.itag
