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Just came across Jon's addition here citing an account from someone who attended the 2013 inauguration of Obama and they mention the jumbotrons showing videos with celebrities to keep the crowd entertained before the ceremony started. Ellen Degeneres, Jimmy Fallon, and Jimmy Kimmel are mentioned, as is Count von Count.
I tried searching for the longest videos possible to get some of that pre-show. If you skim through some of them (i.e. , , and others in this Google search), the screens are sometimes seen in the background when the camera pans over the crowd.