Gary Friedman's excellent book says:
"TIP: This camera has a clip length limitation – 2 GB file size. If you’re shooting in .mp4 video mode (more on that later), then the camera automatically stops shooting when it hits this limit. If on the other hand you’re shooting in AVCHD video mode, then the camera will “close” the first file and automatically start recording a new one while you shoot. The only thing for you to do is edit the two clips together using PMH (which I’ll talk about in this chapter)."