BBC Rewind

[ppppenguin]

It's likely that many of these pieces would have been on film. It was common to use SEPMAG, a separate magnetic film, which would have been played using a sound follower, servo locked to the telecine. It's possible that the vision survives and the sound doesn't. Also a fair number of pieces would have been shot mute, with commentary and music dubbed afterwards. If this wasn't done, or the sound dub doesn't survive, we've just got the pictures.

https://en.wikipedia.org/wiki/Sound_follower
https://www.pebblemill.org/tag/sepmag/