I just installed CentOS 7 on my Lenovo Z500 laptop. Everything works good but when i play online videos (on youtube, vimeo etc.) strange horizontal and vertical lines appears on videos . As I reduce the resolution lines getting frequent. Strangely when I download the same video and play it with VLC player, lines disappears.

I tried different browsers but no luck.

This is a screenshot which i took from youtube(720p) look top end of the book: http://i.imgur.com/wZ0VF5d.png

And this is the same video, same scene downloaded as 720p mp4 and played on VLC player: http://i.imgur.com/JEIiyzi.png

Note: Video players are HTML 5, did not try on adobe flash players.

yes, the html5 video is of slightly lower quality.
maybe it's possible to tweak html5 playback? maybe it's possible to use vlc as a backend/plugin for your browser?
you can also watch youtube straight from vlc with apps like "consoletube" or "gtk-youtube-viewer". there's a few more out there.

Thanks for answer but I solved the problem by switching to Ubuntu Gnome... I will keep CentOS in my servers but the desktop version is a complete disappointment...

It is??

I was quite the fan and not a fan of Ubuntu..

i guess centos 7 is quite different since they finally moved to gnome 3.