The Mysterious Overscan Line

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Chie
Posts: 979
Joined: Fri 31 Aug, 2007 05.03

Watching TV with the overscan area visible, I sometimes notice a thin black line in the top-left corner of some recorded programmes.

The line appeared on an episode of Coach Trip I was watching on 4oD this evening, meaning that for the first time I can show you an example of what I mean:


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Can someone please tell me what causes the mysterious black line?
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Bail
Posts: 1142
Joined: Fri 15 Aug, 2003 21.41
Location: UK

Timecode, generally, depending on how much overscanning you do/don't get you'll see this and white seemingly random flashing dots, basically timecode in barcode format that various broadcast vtrs can use.
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Ebeneezer Scrooge
Posts: 326
Joined: Tue 23 Sep, 2003 13.53
Location: Scrooge Towers

Line 23 is the first active video line (ie the first line that isn't timecode or subtitles/data). PAL defines only the second half of this line as active video, so the first half was utilised as wide screen signalling as it is an easy way to describe the picture format in a way that will guarantee that that information will always travel with the picture.

More often than not, this WSS data is stripped in transmission today as it is deemed ugly. Previous to that, it was there, but most TVs hid it in the overscan area.
Snarky
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Chie
Posts: 979
Joined: Fri 31 Aug, 2007 05.03

Ah, I see. Thank you.

Yes, the flashing white dots and dashes make an appearance every now and then too. It's nice to finally know they actually have a purpose and what that is.
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Inspector Sands
Posts: 368
Joined: Wed 25 Aug, 2004 00.37
Location: London

Ebeneezer Scrooge wrote:Line 23 is the first active video line (ie the first line that isn't timecode or subtitles/data). PAL defines only the second half of this line as active video, so the first half was utilised as wide screen signalling as it is an easy way to describe the picture format in a way that will guarantee that that information will always travel with the picture.

More often than not, this WSS data is stripped in transmission today as it is deemed ugly. Previous to that, it was there, but most TVs hid it in the overscan area.
There is a WSS signal one that you see occasionally on the opposite side of the picture (top right) this is added by some cameras, particually DVCAM, and was fairly common to see about 5-10 years ago. It's fairly easy to turn off in the camera if you plough through the menus and I think it must now get blanked in the transmission stream
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