Transcoders Vs Encoders, Difference in Quality

[Ergasiomania]

From Doom9.net
http://doom9.org/index.html?/mpg/dvdshrink3-main.htm

[[Recently, compressed domain transcoders have reached quite some popularity. These transcoders are based on algorithms designed to recompress an MPEG-2 stream in real-time for TV broadcast. These programs can transcode an entire DVD movie in only a few minutes, because they do not have to decode and re-encode the entire video stream, but only part of it. I will not go into a detailed explanation of the mechanisms used as they are quite involved but basically what you get is a size (and hence quality) reduction per time unit that cannot be rivaled by regular MPEG-2 encoders (though the latter category can yield better quality). DVD2One was the first program to be based on these principles, now DVD Shrink is the first free program to offer this functionality.]]

I am interested in quality video backup. Have been wondering why the speed difference in DVD Decrypter (MPEG-2 encoder?) and DVD Shrink (compressed domain transcoder). I think I have just answered my own question but though this may elicit interesting discussion.

If interested in quality, am I better off to first rip with DVD Decrypter, then edit with DVD Shrink?

[bugster]

DVD Decrypter is NOT an Mpeg-2 encoder.

[Ergasiomania]

Ok then, to the root of my question. Why does DVD Decrypter take 20-30 min to rip a DVD and DVD shrink only minutes?

Oh, and please note the question mark on original post regarding Decrypter

[bugster]

DVD Decrypter does what is says on the the tin. It Decypts the data on the DVD and writes that Data to your HD. The speed of this operation is limited mostly by the rate at which data can be read from the DVD-Rom drive.

DVD shrink will transcode and already ripped DVD (i.e. one that is already decryped and on your HD). The very fact that it does not have to decrypt and that it is working with files on a HD (which is much faster than a DVD-Rom) allows it to work more quickly.


An Mepg encoder, such as TmpGenc, CCE or MainConcept has much more work to do to re-encode than what a transcoder does.