There are so many youtube downloaders are there in internet. but all are not good, and you cant download the videos in original quality. But the best idea to download youtube videos with original quality you can use VLC player as youtube downloader. Here is the way to do that. 
1. Go to the specific video page and copy the URL of the video
2. Open VLC Player, and goto Media>> Open Network Stream 
3. Now you will

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get following window, just paste the URL in that window. 
4. Now you will get video thumbnail in video player. now click on play button. The video will stream now. 
5. Now click Tools>>Media Information. You will get a new window and you will see some information. at the end you will “Location”. Right click on that and click “Select all“, again Right click select “copy“. 
6. Now open Firefox(Recommended),paste this in address bar. 
7. Video will play in your browser. Right click on that and click “Save Video As
 8. The video will get downloading in original quality. 
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