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Discussion in 'TiVo Roamio DVRs' started by TiVoMargret, Dec 12, 2013.
As others have said this is not correct, it still appears on some HD stations as well.
The old analog video sytems had to represent digital data as full white and full black peaks and valley in an analog signal on lines 12-21 of the video signal. This is what you are all referring to as the Vertical Blanking Interval. In that VBI were a whole slew of signals including Vertical Interval Timecode, Closed Captioning, LIDIA (Local ID Inserted Automatically), color and luminance reference signals and others. Analog TVs didn't bother stripping those signals out, they were just masked out by the bezel on your TV.
Unfortunately due to a variety of errors in older systems, often those signals would slip down to higher numbered lines that were meant for active video. Those can often make their way into shows converted to digital. This can also happen if an upconversion isn't done properly even if the VBI was correct on the original.
In the digital TV standards, there are still signals recorded in the equivilent of the VBI known as VANC, Vertical Ancillary Data Space, or even the Horizontal Ancillary Data Space. Tons of information, including multichannel audio, the dolby metadata, VITC, LIDIA, Timecode, etc. fall into those areas.
Now as the whole system is digital, your TV knows not to include the current versions of those signals on the display. On the other hand, the vestiges of the older signals are seen as nothing more than black and white dots on the top few lines of the active video raster. It's often up to professionals like me to wipe them out or zoom the picture up slightly to rid the raster of them.
Good write up! I don't know if it's all correct (I'm not questioning if it is), but it seems very sound, and explains the differing experiences many will have.
Last night, before ever seeing this post, I tried the unidirectional zoom method to push the lines off the top, as well as moving the picture position up. It works, but just leads back to the whole reason this discussion spawned itself: People wanted to see the whole screen while in the Opera Store. These alternate workarounds work, but cut-off picture area when you go back to viewing things that don't require any workarounds (although, it may be better-liked by some, rather than letting the TV zoom the whole picture outwards). Still, good write-up.
I still see it occasionally on OTA recordings. Not in the shows themselves, but during some of the commercials.