Sync audio and video, equipment?
Haha! In movies about movies you always see this clap in the beginning of a shot. The one where the take number and everything is written on with chalk. And they hold it in front of the cam and make one loud clapping noise with it.

Well, if you have ever wondered what this ritual is for, congrats! You have found the problem to the solution ;-))

You get a video frame on which you see the clap closing and at the same time you can see the noise level peeking in the audio recording.

The poor mans version of this is to tell one of your actors to do the clap with her hands.