Copy protection on VHS

[ugly_bob]

Was reading another thread and wondered....
How do you copy protect a VHS tape? I know how they are stopped from being overwritten, but how would you prevent them from being copied?

[khana]

VHS uses the macrovison copy prevention system, it can be defeated using a DVD recorder/player that disables it. Although why anyone would want to copy a video now days is beyond me.

[Ethel]

Khana - people copy videos of films that have not been released on dvd and are no longer available in the shops.

Then they sell them. HIghly illegal. I sold a truly rare video of a tv series on ebay for �87 last year.

Within a week there were dvds selling for �10 each.

That's why.

[khana]

Ethel, I'm sure your right, however, I meant more with regards to a picture quality point of view.

I know I could never go back to VHS.

[chinois]

Protected videos are encoded with lines of copy protection code alongside the lines of video and the lines of sound.

The easy way to understand it is that protected videos have information stored above or below the human hearing or visual threshold. If a signal is recorded above about 20khz then it wont be noticeable to the viewer but if fed in to a VCR or DVD recorder it will be picked up. When the recorder recognizes the signal it scramles the video and makes it flicker or change colour rapidly.

It doesnt seem like there is a way to protect a video once it's been manufactured. I dont know much about the technicalities tho, just the principal :-o