[1.27] Why does playback sometimes freeze for a second?

Some movies, especially those over two hours long or encoded at a high data rate, are spread across two layers on one side of the disc. When the player changes to the second layer, the video and audio may freeze for a moment. The length of the pause depends on the player and on the layout of the disc. The disc producer usually tries to choose a point where the pause will be less noticeable. The pause is not a defect in the player or the disc. See 1.18 for more information.

There is a list of layer switch points in the Film Vault at DVD Review.