YouTube has started showing High Definition videos, following the footsteps of dailymotion.com. If you would like to download some of the HD videos, KeepHD can help you doing that. What you would need to do is, just go to the KeepHD website, enter the URL of Youtube video and press the download button. KeepHD shall give you options to download the video in various formats like High Definition 720p quality, FLV format, MP4 format or even FLVs.
Or simpler way could be go to the Youtube video link and in the URL in address bar; change the Youtube URL by replacing the word Youtube with KeepHD and that’s it!






As far as i know you can download them using IDM too but i’m not positive if they remain in HD. Thanks for the link.