Hello Kristin,
Welcome to the forum! You could try a basic a/b switch. Connect the SA
dvr to one coax input and the dvd player to the other coax input. Connect the output of the switch to your tv. Put the switch in position A when you want to watch programing from the
dvr and put the switch in the B position when you want to watch a dvd. A/B switches are inexpensive (<$10).
HTH,
Rick