I was thinking of D.A. Pennebaker's 1970s documentary about the making of the ''Company'' cast recording.
As for ''A Little Night Music,'' I must admit that's a guilty pleasure: I haven't seen it in many, many years. But I love the new version of ''Glamorous Life'' that Sondheim wrote for the film. I remember the ''Weekend in the Country'' sequence fondly, and adored the brilliant Diana Rigg as Charlotte. Jonathan Tunick also won an Academy Award for his adept Adaptation Score.
(I looked at a clip of Rigg singing ''Every Day a Little Death'' on YouTube, but it's horribly out of sync. )