I've read that the tunnel has been encroached upon by the basements of high-rises which were built sometime after the rail service ceased -- that may be it at 2:55 in the video. Moreover, the lines using it, with the exception of Glendale-Burbank, were all street running after leaving the tunnel, which wasn't all that long to begin with. (I believe that the closer-in hillside ROW of G-B has been built over, and the median in Glenoaks Blvd. between Glendale and Burbank, formerly the PE ROW, has been planted with tall palm trees, now over 50 years old, to which local residents may be counted upon to chain themselves should any attempt be made to replace them with tracks and wires.) All that remains is the Subway Terminal building itself, plus the empty space (shown in the video)above the platform area (5 short tracks). At street level is now the lobby of the apartment (formerly office) building above.
Forget it.