Coronavirus - Impact on live/recorded shows

This same effect is seen on the 2020 Sky documentary 'Race To Perfection', a decent-budget series looking at the history of Formula One. I hadn't seen such previews sneaking through for years!

In fact on many of the 80s EastEnders episodes on Drama, on location shoots you could often see a slither of picture from one of the other cameras at the very top of the screen.

I’ve seen this effect on sports broadcasts when a full screen ad VT is played, usually on American/Canadian sports channels. The image from the currently selected camera is still visible in a thin line around the outside of the VT clip that may be hidden by a bezel on a TV, but not on the web.

Yep - that's likely to be a 'key and fill' VT where the key doesn't include the very top and bottom lines of key, particularly if there was a funky transition to and from the VT.

The VT is keyed, or overlaid, over the background camera - and a line at the top and bottom of the screen remains.

This can also be the case if a DVE-transition is used.

On the current BBC Four TOTPs you often see the Charisma DVE bleed through by a pixel or so all round when it has been cut to with the current on-air camera routed through it. On older TOTPs you also used to see 'blanking errors' which can cause you to see larger strips of background camera.

Overscan on CRT TVs hid a multitude of sins around the edges of pictures, which we now see via our flat screens if we disable overscan or watch online.

On SD shows on BBC HD outlets you may see half a row of repeating dots at the very top of frame. That's a reference signal for the PAL Transform decoder that the BBC designed and implemented for high quality conversion of composite PAL content (it's probably the best PAL decoder in the world - almost totally removing cross colour and cross luma artefacts). Not all the recent TOTPs have gone through it - and they also have 'baked in' PAL decoding artefacts because the Charisma DVEs had to decode prior to their processing...

Wouldn't Dibley have been taped digitally - its way after the introduction of D3 to TVC.

It wasn't made at TVC though, it was made at Shepperton (via an OB unit).

Ahhhh..... that would well explain it looking so messy - and a bad PAL decode too.

AIUI the early series of Dibley were shot using a BBC OB truck (not sure about later series). I think at least one series was shot in the BBC experiment COM3 truck (Component Compatible Composite) which used cameras with modified COM3 PAL coders to hugely improve on the quality that could be achieved. However I don't think Dibley used that aspect of the truck. (The same truck was also used for early 16:9 SD experiments I believe - it was a modified late 70s Type V truck) It's very likely Dibley was shot to D3 and edited D3.

However it's vital to remember the whilst D3 IS DIGITAL it is still PAL or NTSC COMPOSITE. The analogue PAL or NTSC signal is digitised at 4 x subcarrier frequency (around 17MHz for PAL, lower for NTSC) as a single signal, rather than the component digital format that samples Luminance at 13.5MHz and the R-Y and B-Y component colour difference signals at 6.75MHz each (giving a total sample rate of 27MHz - much higher).

D3 tape is not component digital so you still get all the PAL composite cross colour and cross luma artefacts when you decode.

D2 and D3 were PAL/NTSC composite formats where the composite PAL signal was digitised and recorded to tape. They could be used with composite SDI interconnects (though the BBC largely used them as drop-in replacements for 1" analogue C-format composite VTRs using the analogue I/O). PAL composite digital didn't really take off in Europe, but NTSC composite digital had a bit more of a life.

Betacam SP was used in some cases as a low-end replacement for 1" composite VTRs - again as a drop-in - but although it was a component analogue VTR format, if you fed it composite, the results could be pretty poor quality (as the Betacam SP VTR had to decode to component - and baked in some composite decoding artefacts. There was a system called VISC - Vertical Interval Subcarrier - that could be enabled that would reconstruct a much cleaner PAL composite signal if the component recording were replayed on a BetaSP deck and the composite output taken - but it wasn't perfect - and there were a lot of people who didn't understand the importance of using it with composite equipment....)

D1, D5, DigiBeta and the ill-fated DCT (and then DV, DVC Pro, IMX etc.) were the component formats where the colour and luminance signals were recorded separately and thus if shot using component analogue or component SDI equipment from lens to tape you got a clean component recording. However D1 was heinously expensive, and D5, DCT and DigiBeta arrived a year or so after D3 and were a lot more expensive in tape and purchase terms (and offered little benefit in the role of 1" replacement in a composite analogue studio or OB truck)

Arguably the BBC made the right choice in using D3 composite digital rather than component recording to record composite digital shows, as it means that future PAL decoding techniques (such as Transform - which was created in the early 00s) have allowed the recordings to be decoded to a far higher quality than a decoder feeding a component VTR would have achieved in the early 90s. Transform is also 'reversible' Mathematically - which means that a lossless component recording of the Transform output can be re-encoded to PAL composite losslessly (apart from rounding errors) to allow any future, improved, decoders to be used. (The subcarrier in the first half line of 576i active video - which is empty for analogue 575i sources - is a useful helper signal for any future encoder)

There was a shot of a BBC OB truck in the second episode of series 1 - “Songs of Praise”.

That's almost certainly the Type V they were using to record the show in.

I think you’ll find that’s a BB OB truck.

There a BBC OB truck in an episode of The Demon Headmaster too, in the episode where the Eddy Hair show comes to their school