From time to time, many people have serial playback issues with Youtube videos even on fast multi core computers. You tried to reinstall Flash player, try other browser (Firefox, Chrome, Internet Explorer, Opera…) but the video still stops or plays at few frames per second. I saw even that Youtube automatically plays video at HD resolution and that can not be changed even if I click on “Never use HD video”. Cleaning browser cache does not help, too. But gues what! Solution is SO simple!
How to speed up Youtube video
Just uninstall everything named Flash (ActiveX or some plugins), install newest Firefox and it will work! How is that possible? Because, every browser already has generic video codecs and it can play Youtube Flash videos at correct speed without newest Flash player, so you don’t need it for now.
If Youtube later asks for installation of Flash addon, just click on “Do not ask again”.