Hmmm, sounds like some sort of lag if it's happening with emtube as well as standalone files. A couple of suggestions:
1) Try different network connections in emtube if possible to compare (wireless / 3g if available). Also try saving an emtube video for viewing 'offline' and see if you still get a delay.
2) Try running a video from phone memory rather than memory card.
3) Make sure you have nothing running in the background when playing the video.
A couple of things ...
What type of memory card do you have?
You're not listening to the sound through a bluetooth headset / headphones are you? I have noticed a sync problem when doing so.
One other thing ... you say you just copied a divx file to memory card ... did you size it first for playback on the
N95? I always notice a sync issue with a full sized divx.
Let us know how you get on ...