VHS and VCD
 

hello,

Ok for all you video, cd wizards here are some basic stupid questions for you to answer for me.

What is a VCD?

If you have a VHS tape and dont play it after time would it still disintergrate, ie would you loose pic or sound quality?

Dawn

A VCD is a Video CD. It will show mpeg (mpg) encoded files on your computer or on a DVD player that will play VCDs. Not all DVD players will accept or play VCDs but in my experience, most will.
A VHS tape will lose quality just sitting in a drawer without being played. Over time the tape becomes brittle and it can tear, snap etc. If it is played at all, the heads of the tape player cause friction and wear. You can transfer favorite tapes (if available in no other form) to your computer as mpeg files through a variety of Digital Video (DV) devices.

This is a quickie explanation - if you want more technical info - send me a pm or message me from my profile.

Kathleen

Actually, the more serious problem is the fact that the magnetic charge that causes the images and sounds to appear, will weaken in time. A CD or a DVD is recorded with a laser that "burns" bumps in the material. The bumps stay "on" a lot longer than the magnetic charge. Though, some claim that a CD might loose it's info in a few years. I don't quite buy that, but it's been said.

Ice

I just recently read from some science magazine that cd-media will last from 20 to 100 years, depending on the quality of discs. I would assume dvd's lifespan to be around the same.


stoney

Yep, and I read recently that the worst CD's only hold their info for 2 years. Although the guy who said this was from the Finnish Anti-piracy board or something like that. Anyway, I think CD's will last. Why would the material give up?

Ice

Proffesional CD's and DVD's aren't burned, but they are pressed. A master copy would probably be burnt and used to make a molding to press the CD's in the factory.

DVD's sometimes have dual layers, and with this each layer is pressed seperately and then joined together before being pressed onto the plastic disc.

CD and DVD burners that you can buy obviously can't press the discs, so what they do is heat up the disc in certain places to create a sort of dent in the disc, which the computer (or any cd player) reads as a pit.

VHS would not degrade too much if stored properly, but playing them time and time again does degrade the picture; hence I am really looking forward to the Star Wars DVD's in september as my VHS copies (of the pre 97 special edition) have degraded quite a lot, so the picture is very bad.

VCD uses MPEG-1 compression, but only uses a bit-rate of 1150 kbps with a picture size of 352 x 288 .... which means that it is only as good quality as an old VHS tape.
It is possible to use different types of MPEG encoding to produce higher qualities; such as SVCD which uses MPEG-2 and a higher bitrate and larger picture size.
There is also KVCD which uses an altered encoding format to produce higher than VCD quality footage but fitting up to 2 hours onto a single 80 minute CDR.
XVCD is highest quality, and it uses a bitrate of around 3.5mbps, so you'd get close to DVD quality, but only be able to store about 30 minutes on a single 80 minute CD.


DVD is of course the ultimate quality format, using encoding bitrates of up to about 12mbps, and AC3 audio encoding of up to 448kbps.

heh

Thats all very interesting , thankyou all for replying, I have learnt a lot. :D

Mr Anderson, when you say the VHS tape will last longer if stored properly what do you mean by this?

Thanks

Dawn

Ok, we weren't talking about professional CD's or DVD's...

That quality is about the same as a VHS tape out of the box. If done correctly, it's hard to tell the difference between VCD and DVD when looked at on a regular size TV.

SVCD is basically the same as DVD; the codec is the same. The only difference is in the amount of time you want to record on a disk. You can fit about an hour of video on an SVCD disk and again, it's really hard to tell the difference in the picture quality if compared to DVD.

DVD can use any bitrate, and the only real advantage is the size of the disk... You have to remember that a regular PAL television only shows 768x576 pixels. So anything above that is basically wasted. DVD's are good for bigger screens, but on TV SVCD or even VCD are perfectly watchable.


Ice

vcd rnt as good quality as dvds.

now that re writeable dvds r starting to kick around theres some top notch stuff out there. i got the matrix revolutions last night and its incredible quality.