TBC question

[Petergar]

Im new at this. Infact, I just completed registration a few minutes ago. Can somebody explain to me exactly what a Time Base Corrector (TBC) does? I subcribe to a Wireless Cable Digital TV station and notice that on some channels (Satellite downlink) the audio and video does not sync. An example is that when someone is shown talking, the audio would end but the lips are still moving...looks funny. Can a TBC correct this problem and how?

[jagabo]

A TBC will not fix that problem. Although TBC errors can cause A/V desync when converting analog to digital, the signal from the satellite broadcast is already digital.

http://en.wikipedia.org/wiki/Timebase_correction

In short... The spinning head of a VCR doesn't spin at exactly the same speed all the time. That means each scan line of the video varies in length and can be shifted left or right by a small amount. A line TBC makes all the scanlines the same length and realigns them. See the animation in this post:

https://forum.videohelp.com/threads/306272-Computer-video-capture-vs-vcr-to-dvd-combo?p...=1#post1882662

Notice how the vertical line on the left bends and wiggles around while the line on the right remains stable.

A full frame TBC provides a continuous video signal even in the event of a dropout of the VCR signal. It's this type of dropout (or extremely mangled VHS signal) that can cause A/V desync. Missing frames in the digitized video will cause the video to have a shorter running time than the audio.