As I mentioned, there's very little video footage of the two in their roles as silent film comedy legends Mack Sennett and actress Mabel Normand. And this below is no different -- but special, nonetheless.
This is audio of the closing night performance of Mack & Mabel. It begins with Robert Preston's opening monologue, which leads into Bernadette Peters' entrance. You can't make out her lines there too well, but when he asks who she is, interrupting the movie set, she explains "I'm the girl from the delicatessen."
The sound appears to be slightly speeded up, but generally it's fairly audible and a quite a nice bit of history to hear. All the more so because at the 6:30 mark (which you can jump to, of course, if you wish), she sings my favorite song of Mabel's from the show. It comes after she's become an actress, by total unexpected chance, with "Look What's Happened to Mabel." I've always thought that if you looked up the words "adorable" in the dictionary, it would have this number with Bernadette Peters.
This is one of those numbers I keep searching to find video of. I haven't found it yet, but a few years ago there was a TV documentary on Jerry Herman and they actually had about 10 seconds of home movie footage of it, so clearly at least some of it exists. Maybe one day. There is video of the number from other productions, but this is the one I'd love to find.
But at the very least...here's the audio of it.