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  #1  
09-18-2002, 02:31 PM
black prince black prince is offline
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Hi Kwag,

When testing KVCD-LBR, I used min bitrate = 64, max bitrate = 1150,
and cq_vbr = 20. As I increased max bitrate the filesize keep grow-
ing smaller until I put the largest size for max bitrate (10000).
Picture quality stayed the same. What is Tmpgenc doing with max
bitrate. I am not complaining, because this allowed me to raise cq_vbr.
My one minute test clips tested cq_vbr from 20 to 60 incremented by 5.
The filesize slowly decreased to a final decrease of 2.5mb. Will this work
all the time. I tested this on my DVD player and everything works fine.
What is your opinion?

Thanx

-black prince
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  #2  
09-19-2002, 11:55 AM
GFR GFR is offline
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It would be interesting to investigate this with BitRate Viewer.
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  #3  
09-19-2002, 01:16 PM
kwag kwag is offline
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Quote:
Originally Posted by black prince
Hi Kwag,

When testing KVCD-LBR, I used min bitrate = 64, max bitrate = 1150,
and cq_vbr = 20. As I increased max bitrate the filesize keep grow-
ing smaller until I put the largest size for max bitrate (10000).
Picture quality stayed the same. What is Tmpgenc doing with max
bitrate. I am not complaining, because this allowed me to raise cq_vbr.
My one minute test clips tested cq_vbr from 20 to 60 incremented by 5.
The filesize slowly decreased to a final decrease of 2.5mb. Will this work
all the time. I tested this on my DVD player and everything works fine.
What is your opinion?

Thanx

-black prince
Increasing the distance of the CQ_VBR (lowering the value) from a fixed MAX bit rate reference value, is similar to increasing the MAX bit rate from a fixed CQ_VBR value. If you look at the mpeg file with bit rate viewer, the higher the MAX from a fixed CQ, the higher the Q. So quality starts to drop. Same applies the other way around, if you lower the CQ_VBR value while maintaining a fixed MAX bit rate.

-kwag
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  #4  
09-19-2002, 02:47 PM
black prince black prince is offline
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Hi Kwag,

Are you saying that quality is lost when:

Max Bitrate is fixed and CQ_VBR decreases quality decreases.

-or-

CQ_VBR is fixed and Max Bitrate increases quality decreases.

If this is the case what is the best setting and which should be
adjusted (i.e. max and min bitrate or cq_vbr).


-black prince
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  #5  
09-19-2002, 03:05 PM
kwag kwag is offline
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Hi black prince,

The parameters I used on the LBR were chosen with these key points:
MAX bit rate of 1,150Kbps to keep maximum compatibility with most standalone DVD players.
Started with a low CQ_VBR value and increased to a point where further higher values produce larger file size, but not significant increase in quality. Thus, the value of 22 was chosen.
These values are, of course, specific to the GOP/Q. Matrix combination. Other GOP's and Q. Matrixes will throw quality and file size way off. So they were matched as the best "overall" result.

For example, if you use the KVCD 352x240 PLUS, and change the CQ_VBR value to 22, it will look worse that the LBR. That's because it uses a much longer GOP, which behaves differently at the higher CQ and longer GOP.
It really takes some time to find optimal values, because there are many variables involved ( GOP, Q. Matrix, MIN, MAX, resolution ).
If you want absolutely the best quality on the LBR, use a CQ_VBR value of around 28-30. You'll get something, which I think is as good or even better than the regular 352x240 PLUS, but you won't get 180 minutes on a CD-R, which was the main reason to create the LBR.

-kwag
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  #6  
09-19-2002, 09:27 PM
muaddib muaddib is offline
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Yep... I tried the 10000 max and I could see a decrease in quality.
I thought that (because the 10000max) the high action scenes would be perfect. But these are the ones that suffer more... I could see mosquitoes every where.
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  #7  
09-20-2002, 10:25 AM
black prince black prince is offline
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Thanks Kwag,

KVCD-LBR

I did have problems with action scenes when I encoded
"The Matrix". It's seems I didn't notice this with "U571"
because there were not many fast action scenes. I'll
go back to using max bitrate=64, max bitrate=1150
and cq_vbr between 20-30. I am trying to find ways to
increase picture quality and decrease file size. I didn't
mean to send anyone off on a wild goose chase.
Thanks for your explaination about the complexities of
Tmpgenc's min and max bitrate vs cq_vbr,GOP, and Q.Matrix.
I need to read more. I am curious about Q.Matrix and GOP.
Is there any good reading sources on this subject.

-black prince
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  #8  
09-20-2002, 10:52 AM
kwag kwag is offline
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Quote:
Originally Posted by black prince
I didn't
mean to send anyone off on a wild goose chase.
Not at all . That's what made KVCD a reality! Many crazy settings and experiments, and many "Nay" sayers in "other" forums that said it couldn't be done and pushed me to the limit, and now they're silent and can't make a single comment
Keep up experimenting, that's what makes this a lot of fun
I'm personally using CQ_VBR of 30 if the movie is around 2 hours or less. I'm getting better results with the LBR than with the regular 352x240 PLUS . So try CQ_VBR=30 for ~2 hours movie and CQ_VBR=22 for ~3 hour movie. Those numbers are working excelent for me

-kwag
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  #9  
09-20-2002, 10:58 AM
muaddib muaddib is offline
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Hi black prince!

I had already got into this "wild goose chase" before. Kwag took me out of there.
Look at this topic -> http://www.kvcd.net/forum/viewtopic....ighlight=crazy
I made some more tests after your post just to make sure... you know, never loose the faith.
Keep testing!
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  #10  
09-20-2002, 01:59 PM
black prince black prince is offline
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@Kwag and Muaddib,

Thanks for the encouragement. I didn't realize anyone else
was doing similar max bitrate tests. My stand-alone DVD
player is very flexible with bitrates and it plays all KVCD, while
others won't touch them. I Like pushing the envelope when it
comes to picture quality. These templetes are ideal for that.

I have a question (I hope it's not stupid). C3D is very good
at reducing noisy source, such as vhs capture, etc. My source
is DVD with no noise. How will it improve picture quality?
The settings I am using (1,0,0,7,7,0) are not having any effect
with the "misquito effect" at low cq_vbr settings. I am tempted
to re-encode a noisy KVCD-LBR using C3D, just to see if there is
improvement.

-black prince
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