Windows 7: Video and audio does not sync from laptop to tv monitor

Hi everyone, my problem only occurs when trying to watch movies or tv shows I've purchased from itunes. The videos seem to play fine at first, 20 min in however, video starts getting out of sync with the audio and lags behind. This only happens with movies and shows in itunes though, watching movies and shows from hulu or cbs.com are perfectly fine no issues at all. My laptop is just an hp dv6 connected to a tv monitor with hdmi cable. I am not a tech guy at all, i udate my laptop as much as possible and still have no clue how to fix this problem. Any help at all would be appreciated.