If you hunt around ( nasaspaceflight.com is a good start ) you can find these videos in full. Not long after ET sep, perhaps a minute, the signal turns to noise and the videos end.

From:http://216.239.59.104/search?q=cache:PRbM_kDQm3QJ:www.nasa.gov/centers/marshall/pdf/114016main_ET_SRB_Cam_FS.pdf+shuttle+et+camera+radio&hl=en&ct=clnk&cd=1&gl=uk&client=firefox-a

"The video will be down-linked from the tank during flight to several different NASA data receiving sites, and then relayed for broadcast on NASA TV. The ground stations include PDL, the NASA Tracking Station at Ponce DeLeon Inlet 35 miles north of Kennedy Space Center, Fla.; JDMTA, the Air Force tracking station in south Florida at Jupiter Inlet; MILA, the NASA tracking station at Kennedy; and Wallops Flight Facility, Virginia Eastern Shore."

and

"The camera’s battery pack includes 20 nickel-metal hydride
batteries—similar to cordless phone battery packs—that will
provide approximately 28 volts DC. Though the batteries will last
for about 70 minutes, the camera is expected to operate about
18 minutes during launch countdown and ascent."

This suggests it's a ground-station visbility issue that results in the signal cut off rather than a power issue, and also that it's not a TDRS relay being used.

Doug