I download movies from the Internet. Each movie is between 0.7-1.5 G.
Most of them are in AVI format (divx or xvid). I have DVD burner and I
can curn them into a DVD, 2 hours per one DVD -R. Alternatively, I
know how to burn them, as VCD, into DVD media, so I have 3 movies per
one DVD media.
The question is: Do I have any differences in quality or other aspects
between the 2 methods? Are there any advantages to dedicate 1 DVD
media per movie, while I can burn 3 movies, as VCD's?
I was told that since the movies downloaded are already compresses, It
is not possible to "increase" the quality bu burining as DVD, whic
will require a lot of space. Is this correct?

Hello there dealeng!

There is probably no benefit to burning to any particular format. The
movies are already compressed, and in fact, have had a lot of
information stripped from them already. This technique is known as
"lossy compression". It relies on the fact that the human eye looks
more at some things than others: for instance, the eye will be more
drawn to lines and edges, than it will to textures. This means, for
example, you'll be more likely to notice the shape of someone's face,
rather than the texture of their hair. Similarly, you're eye will be
drawn first to a moving vehicle, rather than a parked one. So when the
DivX or xvid codecs compress the video, they throw away some
information judged less important, or they reduce the quality of an
area judged "boring" to the eye, in order to save space.

So if you convert them to any other format at all, other than the one
you downloaded them in, it's likely you're going to lose even more
information (unless you pick a lossLESS format, which would take
several DVDs to fit one movie on). If the choice must be between DVD
and VCD, then DVD usually loses less information than VCD, and I would
pick this format.

I hope this helps! If anything's unclear, then please use the "request
clarification" feature before rating this answer.

Regards,

--seizer

References:

http://whatis.techtarget.com/definition/0,,sid9_gci214453,00.html
http://www.atis.org/tg2k/_lossy_compression.html

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Request for Answer Clarification by dealeng-ga on 18 May 2003 02:36 PDT

Thanks.
I understood it in general but not speciaifically to my case:
While concerting AVI to VCD, do I loose someting?
Sizes are about the same (700 mega AVI will become 700-800 mega
VCD(mpeg1))
What about by converting AVI to DVD? Do I loose someting?
I believe that there should be no real difference. Is this correct?
I also believe that, for movies, burning DVD will give you advantage
and better quality if you copy a DVD or using DV camera but not for
files downloaded via the internet. Is this correct?

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Clarification of Answer by seizer-ga on 18 May 2003 03:20 PDT

Hello again!

Every movie file is compressed with something called a codec. DivX,
VCD (MPEG1), and DVD (MPEG2) are all different ways of doing this
compression.

So if you imagine a raw, uncompressed source - such as the original
reels of a film. If you compress from the reel to DivX, you lose
something. If you compress from the reel to VCD, you lose other
things. If you do the same to DVD, you lose another different set of
information.

If you THEN convert from an already compressed source, to another
compressed source, you lose even more information.

So yes: converting from AVI to VCD will lose more quality (although
you may not be able to notice it), and converting from AVI to DVD will
also lose quality (though yet again, you may not be able to see this).

You're right about DVD being better quality - but don't forget, you
can never increase the quality of the original source: you can only
hope it stays the same, or doesn't degrade too much.

Hope this helps,

--seizer

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Request for Answer Clarification by dealeng-ga on 18 May 2003 04:11 PDT

Thanks.
I regret but I still need more clarification:
I can not burn and watch movie in DVD player, connected to the TV AVI
format. So I HAVE to convert it. The question is if by coverting to
VCD i am loosing more then by coverting to DVD and if this is
something that I can notice.

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Clarification of Answer by seizer-ga on 18 May 2003 06:04 PDT

Yes - if you're playing it in a standalone DVD player, burning as a
DVD will produce a better quality copy than using VCD - and you
probably will be able to notice the difference, especially in high
motion scenes.

(See here: http://www.studiomagicbymike.com/dvdvcd.html )

Hope that clears things up!

--seizer

This was an excellent and educational answer, seizer-ga. I would have
awarded you 5 stars if I had been the questioner.

Not necessarily, while the answer was certainly educational, he failed
to address some of the questions that had been asked. Yes,
recompression does result in further loss, but one must realize that
VCDs and DVDs have very different bitrates, resolutions, and
compression algorithms. Divx is a much more compressed format, and so
can store more information in a similarly sized file. It depends
largely upon the resolution of the original files, as you would want
to have one as close to that of the original as possible (if it is 352
x 240 you probably want to do VCD or have a border around the image or
have a XVCD or modified SVCD (upscaleing resolution can be nasty), the
same applies for vice versa).

Exactly:The answer was too general and did not answered my question in
full:
I was not asked about my current resolution fro example.
I also expected some idea about percentage of loss from XVID to VCD,
from XVID to DVD etc.
The answer also contradicts itslef by advising once that "the
difference is probably not notified" and once the opposite.