for google chrome and linux users ,the solution that is most popular to overcome this problem and watch youtube videos is going to tools > task manager ,kill process ,load again the video of interest and done !
even if it not works try disabling libpepflashplayer , by typing at browser bar : chrome://plugins/ .
If you want to be more thorough , you can remove ~/.config/google-chrome/PepperFlash
either way it worked for me thnx to askubuntu here
zeracuse 