The crux of British TV host David Frost’s historic interview with Richard Nixon — which inspired a hit play and Ron Howard’s upcoming film — was ?devoted to Watergate, though it accounted for only 2 of Frost’s 12 taped sessions. (Highlights of the remaining footage are due next year.) The sight of the disgraced ex-president close to tears is riveting, but the rest of the exchange can be a slog for those not well versed in the scandal and its players. Frost/Nixon: The Original Watergate Interviews offers 23 new minutes of self-congratulatory recollections on Frost’s ?journalistic coup, but one yearns for a Pop-Up ?Video version to fill in more of the non-Frost history. B?