In a video on demand (VOD) system, methods and apparatus are provided for seamlessly switching back and forth between two pre-encrypted files having changing encryption keys. Such switching back and forth may be required when a VOD server stores both a "normal" copy of a movie and a "special" copy such as a "trick-play" version for, e.g., fast forward and rewind effects. Instead of using keys with changing parities in both streams, the special stream is encrypted with keys using the same parity (even or odd), while the normal stream is encrypted with one dynamic key (odd or even) and one fixed key (even or odd). Other special streams, such as scene branch streams and alternate angle streams can also be accommodated.