Hi there! Because the forum you originally posted in is for beginners trying to learn the basics of Photoshop, I moved your question to the Photoshop General Discussion forum, where you'll get more specialized help.
To help others help you, please read through this article and provide any additional relevant details.
Quite likely it is a video card/driver problem. CS6 puts a lot of strain on it and you need good drivers. For ATI Catalyst 12.8 is the most stable.
You info is far too vague. We don't know anything about your system or your render settings. That aside, such a question will only lead to endless discussions about basics of video compression, so simply look them up on a web search because pretty obviously you haven't yet...
It sounds like you're encoutering Frame Skipping - Photoshop is skipping uncached frames to keep up with the audio.
You'll need to turn the audio off, play the video once to cache all the frames, then replay with the audio on.
Here is a short tutorial I made for this issue: