The Wikipedia article on the Telstar satellites from the early 1960s says that in order to facilitate transatlantic television signals (where the US had the 525-line (480 visible) NTSC system, and the UK's BBC had a 405-line system) the BBC had room-filling video signal conversion apparatus.
The standards 525/405 conversion equipment (filling a large room) was researched and developed by the BBC and located in the BBC Television Centre, London
I'm curious how this conversion equipment setup worked. I know that delay-lines are used in relatively modern analog television systems (such as PAL), but it's implied a delay-line system could really only buffer a single line - rather than multiple entire frames to cover a frame-rate mismatch.
Today, to convert video of one-frame-rate and resolution to another necessarily involves modern interpolation algorithms operating on multiple digital frame-buffers - but [Wikipedia implies that the capability for video framebuffers in the 1960s simply didn't exist. I know that but it wasn't feasible to bufferm
(I'm assuming that they had a fully electronic system and that they weren't employing tricks such as using a 525-line TV-signal projector to illuminate a screen that was being simultaneously filmed by a 405-line camera for onward distribution.)
My question is: how could an electronic television signal frame-rate-and-resolution conversion system be implemented using 1960s-era technology?