Tvheadend

I exercised Yoga recently. when I was in home, I as watching the yoga video on YouTube as exercising. But sometime I must go some places where is no wifi so that I can't online watching the Yoga video. Therefore, I want to download yoga video from YouTube.[[www.videoconverterfactory.com/tips/yoga-download.html]]
I tried some methods on Google, but it too difficult for me to change some codecs. So any easy way can download from YouTube? Thanks in advance!