Such is widely reported. Since the TV is not a PC you have to be careful how you encode content. And to repeat this again, you must encode the content in a way that it works. It's not a bug in the TV as it's not a PC. It's an encoding issue.
I have Samsung UE40C6000 and I've noticed that when playing some video formats (avi) there is an annoying audio delay. I'm using Media Play (tried through USB and DLNA) and I tried to play Sunshine in HD quality and everything was okay - no sync problem, but when some episodes of How I Met Your Mother (for example) were played audio was delayed and I can't figure out why it's happening (on PC no delay). Satellite and Xbox work fine, so it seems to be "Media Play" issue. Firmware of the TV is up to date.
Has anyone else experienced this problem? Could anyone help me with that, please? I'm lost..