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Your URL was:  http://save-video.mp4?http%3A%2F%2Fv16.lscache5.googlevideo.com%2Fvideoplayback%3Fip%3D0.0.0.0%26sparams%3Did%252Cexpire%252Cip%252Cipbits%252Citag%252Cburst%252Cfactor%26itag%3D18%26ipbits%3D0%26signature%3D7B6F4D9C4B456B7A0F11E62F9662AC0C4C971696.70A84F426E16CCB23A26BF59289625A3F1F5E546%26sver%3D3%26expire%3D1246611600%26key%3Dyt1%26factor%3D1.25%26burst%3D40%26id%3D962ef283c9248a37

The URL must be like  http://www.youtube.com/watch?v=KPtX7hak0Qs