Black bars fluctuating...

[FallenAngelII]

How come when you have a DVD-VOB, the black bars change size inbetween scenes? Like for "The Simpsons", there might be 4 pixels of black bar on the right side of the screen. However, fast forwarding to another scene might give you 6 pixels and yet another 2.

Why? Shoddy work when transferring to DVD? I can't imagine them airing TV episodes with fluctuating black bars.

[guns1inger]

The Simpsons is created as 4:3. On a 4:3 TV the edges are no visible due to overscan, so small differences like this are not seen. It is this type of issue that prompted overscan in the first place.

[gadgetguy]

The Simpsons is created as 4:3. On a 4:3 TV the edges are no visible due to overscan, so small differences like this are not seen. It is this type of issue that prompted overscan in the first place.

Huh? I thought overscan was a unavoidable condition of the design of tube TVs and the producers of TV content found that they could take advantage of it.

[Cornucopia]

No, it was the other way around...

As much as engineers tried (in those days) to calibrate their systems, there was no way to always, consistently give an in-focus, rectilinear (not curvature-distorted), wall-to-wall/edge-to-edge signal to the tube. Good thing about tubes was that it was EASY to adjust the overall deflection voltage to adjust the screen size and position (as witnessed on menu settings of modern PC CRT monitors). So---just hide the mistakes.
Now, the "mistakes" are much, much less. But they're there. You just found one.

Scott

[gadgetguy]

No, it was the other way around...

As much as engineers tried (in those days) to calibrate their systems, there was no way to always, consistently give an in-focus, rectilinear (not curvature-distorted), wall-to-wall/edge-to-edge signal to the tube. Good thing about tubes was that it was EASY to adjust the overall deflection voltage to adjust the screen size and position (as witnessed on menu settings of modern PC CRT monitors). So---just hide the mistakes.
Now, the "mistakes" are much, much less. But they're there. You just found one.

Scott

Your explanation seems to confirm what I said, not dispute it. The overscan area was created, not to cover "errors" in the broadcast content, but to overcome the limitations of the receiving hardware.

[edDV]

No, it was the other way around...

As much as engineers tried (in those days) to calibrate their systems, there was no way to always, consistently give an in-focus, rectilinear (not curvature-distorted), wall-to-wall/edge-to-edge signal to the tube. Good thing about tubes was that it was EASY to adjust the overall deflection voltage to adjust the screen size and position (as witnessed on menu settings of modern PC CRT monitors). So---just hide the mistakes.
Now, the "mistakes" are much, much less. But they're there. You just found one.

Scott

Your explanation seems to confirm what I said, not dispute it. The overscan area was created, not to cover "errors" in the broadcast content, but to overcome the limitations of the receiving hardware.

There are many sins hidden by overscan and screen H position through edits one of them. This was a much bigger deal back when editing was done with composite video (e.g. 1" Typce C or D2/D3 tape). Back then you had to have a precise relationship between subcarrier to horizontal phase or the picture would shift horizontally at edits. Most effects editing requires frame positions to match at the edit point or the viewer will see the H jump. If the edited frame is visually different, you would still see the picture edges shifting in H at edit points. All this was solved by editing with component rather than composite video. Older composite masters can be full of h shift errors if the post house enginner didn't manage SC/H phase. PAL is more affected with greater H shifts.

http://www.hamlet.co.uk/support/apps/sch.html


PS: The problem is similar to editing on GOP edges in MPeg2. Composite PAL video must be match edited to a eight field sequence (4 Frames). NTSC has a 4 field sequence (2 Frames). Get that wrong and the picture jumps in H position at the edit.