Funnily enough, the clip posted further up this page is from a 16:9 episode, it just seems to have been cropped to 4:3 for some reason.
Back in the late 90s and early 00s lots of people had 4:3 CRTs and the default setting for digital set-top boxes was for 4:3 centre-cut (not letterbox).
If you recorded your set-top box output to VHS or DVD then it would be in the same format that you were watching in, which is why a lot of 4:3 centre-cut clips pop up on YouTube from early 16:9 shows I suspect.
Watching widescreen programmes on a 4:3 set was never the best experience. 4:3 centre cut-out was ugly because it cut off vast amounts of the picture, especially when programmes were being shot as 14:9 action safe (4:3 graphics safe). 16:9 letterbox reduced the picture size too much for many programmes where, let's be honest, having a wider picture wasn't a necessity.
I owned a Philips Freeview box which had a 14:9 letterbox mode and it was great - gave you the full 'action safe' picture without too much of the picture size being reduced, which of course is why it was used for analogue, but it was disappointing that very few digital receivers had it as an option.
Funnily enough, the clip posted further up this page is from a 16:9 episode, it just seems to have been cropped to 4:3 for some reason.
Back in the late 90s and early 00s lots of people had 4:3 CRTs and the default setting for digital set-top boxes was for 4:3 centre-cut (not letterbox).
If you recorded your set-top box output to VHS or DVD then it would be in the same format that you were watching in, which is why a lot of 4:3 centre-cut clips pop up on YouTube from early 16:9 shows I suspect.
That clips from an official BBC America YouTube channel though, promoting a DVD release, not an off-air recording (maybe the fact it's BBC America might be why it's 4:3 though).