Quantcast CQmatic: First Time Using, Odd Result? - digitalFAQ.com Forums [Archives]
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08-01-2003, 08:54 AM
Thomas Davie Thomas Davie is offline
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It took me a while to download CQMatic because I simply did not understand what it was, or what it did. A little bit of reading (plus a lot of difficulty in getting the file size or CQ set correctly while using adaptive scripts) led me to take the plunge.

Here's the setup.

My copy of Harry Potter: Chamber of Secrets
----------------------------------------------------
Length: 160 minutes, 57 seconds
Full screen format
Average Bitrate from Moviestacker: 553
Using D2S 1.13b2, Avisynth 2.52, and a motion adaptive script.
Encoding to 352x240
Audio Bitrate set to 128
800 MB CD size

Without using CQMatic, D2S has a devil of a time getting the CQ right. I find I have to stop the program, recover and set the CQ to a fixed value of 17 (that's right). It then encodes and muxes to a final file size of ~759 MB. Using CQMatic 1.04, it selects a final CQ of 12.56 (this is with me feeding in the bitrate and time from Moviestacker into CQMatic, and loading the AVS file, and setting it to predict only).

So why the discrepancy? Is it just because of the non linearity of CQ? At this low level, it makes quite a difference in quality from 17 down to 12.56

Any ideas? Will the numbers chosen for manual selection and CQMatic selection get closer as the movie time gets smaller and average bitrate increase?


thanks for any ideas (and thanks for a fine program Kwag).

Tom
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08-01-2003, 10:32 AM
rhino rhino is offline
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a CQ of 12 seems very low. I did this film using Tok last month at 352x288 (PAL) with audio of 112kbps and the CQ was in the 60's using the MA script. At 352.240 I would expect good results with the MA script.

Cheers,
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08-01-2003, 12:11 PM
Thomas Davie Thomas Davie is offline
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Quote:
Originally Posted by rhino
a CQ of 12 seems very low. I did this film using Tok last month at 352x288 (PAL) with audio of 112kbps and the CQ was in the 60's using the MA script. At 352.240 I would expect good results with the MA script.

Cheers,
It is very low, but I'll change to 112kbps audio and see what difference that makes. Was your version of the movie widescreen or fullscreen?

I didn't use Tok. This is the procedure I used.

a) Started D2S with adaptive script
b1) As soon as TMPGEnc starts the trial encoding, I stop everything, fire up CQMatic, load the AVS file....or
b2) Let D2S zero in on the CQ, stop the procedure myself and recover, reload and continue, but setting a fixed CQ that I can find from watching the iterations.

In b1, I determine the movie length and average bitrate from Moviestacker and feed it in to CQMatic.


That's all that I can think of at the moment.

Tom
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08-01-2003, 12:53 PM
rhino rhino is offline
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The movie was wide screen which helps to get a better CQ. I use Tmpgenc to do all encoding so I have no experience of D2S.

Cheers,
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