It happen when you found a beautiful piece of music, and you want it to be repeated without a need to hit the button to play it again.
1 - Using a website :
They are Websites that provide that kind of service.
The Best of them :
After seeing the video, copy the link and insert it to one off the websites mentioned before. You can choose how many times you want It to be played, and the part exactly you want to play...
yourepeat has a chrome extension to repeat YouTube videos at the click of a button.
For me the best one is listenonrepeat because It keeps the cache.
2 - Using Mplayer :
You need first make mplayer loop :
To repeat or loop an Audio or video in Mplayer
And then, view the video by using the command which starts with mplayer. It requires youtube-dl in order to run the command successfully.
mplayer -geometry 100%:100% -xy 500 -ontop -cache-min 2 -cookies -cookies-file /tmp/cookie.txt $(youtube-dl -gf 18/34 --cookies /tmp/cookie.txt "URL")
Remember to change URL by the link of the YouTube video.
This command will show a mplayer top window in the right bottom corner playing and replaying the video.