Weird line at the top

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Martin Johnsson

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Weird line at the top

PostTue Jul 25, 2017 10:37 pm

When I capture videos with my Blackmagic Intensity Shuttle Thunderbolt, the video appears a bit strange in the top. (look at the attached picture)

Only with composite and component, not if I use HDMI.

Is it something wrong with the device or is it just normal?
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Massimiliano Celindano

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Re: Weird line at the top

PostWed Aug 02, 2017 2:19 pm

It's absolutely normal. You will notice the same pixelation even with HDMI but in another position.
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Martin Johnsson

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Re: Weird line at the top

PostSun Aug 06, 2017 9:36 am

So there is no way to avoid this?

Do I have to crop the captured video to make the top become "normal"?
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Massimiliano Celindano

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Re: Weird line at the top

PostTue Aug 08, 2017 2:05 pm

As far as I know there's no way to avoid it. Cropping wil surely do the job, but I would not recommend it.
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Colin Barrett

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Re: Weird line at the top

PostWed Aug 09, 2017 9:37 am

This is because, in an old-fashioned, standard definition, analogue TV world a frame of a TV picture was created by two interlaced scans of lines - alternatively odd lines (1,3,5,7,9 etc) and then a flyback to the top halfway point to fill in the even lines (2,4,6,8,10 etc). Each scan set is called a "field" with two interlaced fields producing a full frame with either 25 (PAL, SECAM) or 30 (NTSC) frames produced per second.

So........... the step at the top of a digitised frame is displaying the half-line scan start-point of the second field in the whole frame sequence. On an old-fashioned CRT TV screen all this is outside the normal picture display area (known as "overscan") but of course when you're creating a digitised recording from the analogue source you see everything.

I'm currently digitising to ProRes422 a load of material from a pile of professional-quality NTSC Hi-8 recordings and lots of this stuff becomes apparent (top and bottom) when viewing on a 4:3 CRT monitor in "under scan" mode.
Blackmagic Teranex 2D, Ultrastudio Express, Intensity Shuttle (Thunderbolt), H.264 Pro Recorder (all Mac OSX) & lots of old VTRs used for digital archiving of legacy video formats for major libraries, broadcasters, universities and public archives.

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