Re: [dvd::rip] what is the effective ratio?

flash@xxxxxxxxxxxxxxxxxxx wrote:

> Is there any link or docs that explain the effective ratio vs physical ratio 
> in the clip and zoom tab? I can't figure out how they relate and what the 
> effective ratio means and does.

Hmm, interesting that it took so long until someone asks this 
question... it's indeed a good question... ;)

At first I have to say: when I "invented" this two terms my 
understanding of DVD aspect ratios wasn't fully developed as it is now 
(for my excuse: this was in the really early days of dvd::rip ;). With 
other words: today I'd name these things different resp. would do a 
completely different approach (and I plan to do that).

Ok, having that said I try to clarify things... ;)

In general the term "physical ratio" means the width divided through the
height of the actual image. E.g. 720/480 = 1.5.

"Effective ratio" tries to say "the movie's aspect ratio which should be
achieved if it's played". Everything clear? ;) Ok...

On a NTSC DVD a 16:9 movie is recorded at 720x480 (=1.5) which is 
obiously not 16/9 (=1.77). That means we don't have square pixels (as 
used on a computer monitor or TV screen). A DVD player scales the image
accordingly so the pixels are square again and a circle is a circle and
no ellipse. The whole thing is called "anamorphic" recording.

If you use dvd::rip's auto presets dvd::rip takes care to scale the 
image right. And to give the user the feeling that a 4:3 movie is now 
scaled correctly dvd::rip prints an "effective ratio" of "4:3" (or 
"16:9" if it's a 16:9 movie) under the 2nd image (which shows the scaled
image).

The 3rd image shows the 2nd image wich clipping applied, that's why you
get the same "effective" ratio - because the ratio (resp. "pixel 
squarness") is affected only by scaling operations. The physical ratio,
of course, changes - but that's not important.

So what do we learn from that?

1. The printed physical ratio is not important at all

2. The effective ratio of clip1 is useless at all
   (because it's not useful until scaling is applied)

3. The printed effective ratio of the zoom and clip2 states
   should be the same as the aspect ratio the movie is encoded at,
   otherwise the image is distorted in some way

What I learn is that it's time to change these things on the GUI. I 
think the term "pixel ratio" would be better and should be 1.0 at the 
end - telling the user that he has square pixels, what's finally the 
goal of all this.

Hope this helps in some way... ;)

> How can the effective ratio stays the same when the physical ratio change so 
> much between zoom and second clipping? And why does the efective ratio not 
> change to 16:9 considering 1.82 is much closer to 16:9 (1.7777) than 4:3 
> (1.3333)

To answer this directly: it looks your movie is recorded at 4:3 (which 
is anamorphic as well, because 720/480 != 1.333 = 4/3). In the meantime
we know the physical ratio of clip2 is useless at all, only the 
effective ratio value is important. Since dvd::rip prints "4:3" here 
everything looks perfect in my eyes ;)

Regards,

Joern

-- 
LINUX - Linux Is Not gnU linuX
pgpnbAiJiFehC.pgp
Description: PGP signature