Technical question about CODEC's

wvg wrote on 8/20/2001, 9:57 PM
Most of the templates use a CODEC that employs compression. I understand that while editing, watching the preview you are seeing uncompressed video. My question is are video compression schemes similar to what happens to a file placed in a ZIP archive and nothing is actually lost or is the compression destructive like when you convert a TIFF image to a JPG?

It seems like the latter, yet if I take a MPG file and then render to uncompressed AVI the file size grows dramatically and the quality if you render it back to MPG generally improves with the file size going back down again, so somehow something seems to be happening What am I missing?

Comments

discdude wrote on 8/20/2001, 10:11 PM
There are two types of codecs:

Lossless: Similar to a Zip, no information is thrown out. The compressed file is exactly the same as the original. I don't know of very many video codecs that are lossless. The only one that comes to mind is Huffyuv.

Lossy: Similar to a JPEG, information is lost. The compressed file is not the same as the original. Most video codecs, like DV(DCT), MPEG, Windows Media, MJPEG, DIVX, Cinepak, Sorenson, etc, are lossy. Usually, you cannot recompress these type of files more than once before you start to get heavy artifacting.

I don't know why you would get better results when you recompress a file unless you do some nice image processing (HSL adjust, blurs) in VF2. Otherwise, it's pretty much garbage in, worse garbage out when it comes to codecs.