AVi etc to DVD Question

[Dj Demon]

Heres something i dont understand

When a film is encoded back up to dvd, origanal file is say 700mb and the output file is 4.2Gb

Where does the encoder get enough info to make a 4gb file, because the origanal quality has been reduced to get the 700mb file in the first place
Now u cant put back what isnt there so does it pad the encoded file with blank frames(Im guessing),or special data that u cant see??(still guessing)

And the second bit is..
If it is streching/padding/whatever why is it not possible to make a 700mb vob set and cut down on the time spent etc

Im sure there is a large technical explantion for this and hopefully someone can give me an easy ish answer

Dj Demon

[fmctm1sw]

Not real sure I follow your question but what about bitrate? File size is dependant on bitrate...

[mats.hogberg]

I'm not sure as to how you think this works, but basically it's like this in AVI to MPG (or any other format conversion):
The source file is read, and every frame decoded to a still image. The quality here depends on how the original encoding was done.
This still image is encoded using the target codec. How close this new encoded image resembles the image that was decoded from the source is determined by the bit rate - how many bytes each pixel gets.
The quality of the still image can't be determined by the encoder. It just tries to encode it to be as true to the still as possible.

/Mats

[Dj Demon]

Thanks for the explanation ive had a chat with my mate and we understand that now

So presumably thats why u cant make a 700mb vob set because the avi/etc has been upped in quality to fit the larger bitrate which creates a larger file?

[mats.hogberg]

the avi/etc has been upped in quality

Well, not exactly. Quality can never be "upped" when converting. What once was lost when the AVI was encoded is lost for good.
It's just that the DVD mpeg is closer to the AVI, than the AVI is to whatever was the original.
Also, the resolution is (usually) increased (which requires a higher bit rate to maintain quality). Add to that the fact that mpeg2 is not as efficient as DivX, Xvid and other mpeg4 codecs, you end up with a file that's like 4-5 times bigger, but doesn't look any better.

/Mats

[Icu2]

i would explain it like this..... Differant files types.. use differant converstions...have differant compression...uncompresd Avi is like 100mg per Min (well i dont think so but lets just pretend) and Divx or xvid is like 1 mg per Min.

Differant types differant codecs have differant size ouput files no matter on what the length of the original file.

A 10min file wont always b 1 gig no matter what you convert it to.

ICU2

i know u already understand but maybe sumone else reading this who has the same question might not so im just explaing best i can. Hope this helps sum more. or i proly have the question totaly wrong.

[Dj Demon]

No u got it right icu2

Thanks to all for the help