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There's a logistical problem with relying on the network truck to feed replay footage. The producer in the truck has to focus on directing the on air content. It would be tough for the truck personal to respond to the producers instructions for on air content and officials requests for playback of various camera angles simultaneously. I don't think the networks nor the NFL are willing to commit to the level of cooperation between the truck and the officials that would be necessary to make it work.
Also, what happens if the network producer, for whatever reason, doesn't provide a critical angle? Fans are quick to scream foul play when the refs make a mistake. Imagine what the outcry would be if the network made a mistake. Take the Patriots vs Saints game coming up. If the networks were providing replay footage and didn't provide an angle that would give the Saints a winning score, Saints Nation would storm the trucks out of protest for the network fixing the games for the Patriots.
I think the better solution is for the NFL to have at least two servers to playback the footage. The odds of two servers freezing up at the exact same time are pretty low. And if they don't already, they should replay footage after every play just to make sure the system is working. That way if it freezes up during play back of a non-challenged play. They have time to reboot the system.
It is recorded on 2 servers in the replay booth. http://www.soundandvisionmag.com/fe...e-nfl-instant-replay-system.html?print_page=y the failure occured at a switch controlling the servers. is what he said.