I found this in the manual.
309 SERVO/AV REFERENCE
SEL Select the servo reference signal.
AUTO1: During recording, the input video signal is used as the servo reference
signal. During playback, the signal selected by F2 (REF VID) in function menu
page P03: VID PROC is used as the servo reference signal. If the signal
selected by the F2 (REF VID) in function menu page P03: VID PROC is not
connected, an internal reference signal is used.
AUTO2: When F2 (REF VID) in function menu page P03: VID PROC is set to
“REF”, and any of F2 (INS TC), F3 (INS CUE), and F5 (ASSEMBLE) to F10
(INS A4) in function menu page P07: E.PRESET is lit, the reference signal for
video/audio signal processing is locked to the input video signal.
EXT: The servo reference signal is forced to be “EXT” (an external reference video
input signal is used).