I'm about to purchase my first DVD player, and don't understand some of the terminology. Reviews of several players complain of layer changes of 1 to 4 seconds. What are layer changes? Does the screen go blank? How often does this occur? My TV is old, so I don't want progressive scanning. At present, am leaning toward the Sony DVP NS 400 or the Pioneer DVD 440. Any recommendations either way would be most appreciated.