Quantcast Bitrateviewer: Value Considered as a Minimal for Quality? - digitalFAQ.com Forums [Archives]
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01-14-2004, 06:45 AM
Dialhot Dialhot is offline
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Hi all,

I'm not sure anymore about a little thing when I use bitrateviewer.

Let say I have two video, one with Qfactor = 5 and the other with Qfactor = 10. Which one is supposed to be the better ? In other word, the higher the Qfactor, the better the quality, or is it the opposite ?

An other question : is there a value considered as a minimal for quality acceptance ? I mean a value that you can say "above that, the video is good, under that it's awfull" ? Or perhaps a range value insteed of a single value ?

In fact I need a documentation for that tool
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01-14-2004, 06:57 AM
incredible incredible is offline
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A bit precise now, but as a thread is read by all, this could discover some Quantisation secrets.

In regular, the Q should stand for quantsation and the more quantisation will be done, the more the quality gets worse.

Its like when you do very cutting settings on DCTfilter()
Just go with some more values from right to left set to zero and you will see the effect of Quantisation.

DCTfilter(1,1,1,1,1,1,0.5,0) and switch to this one:
DCTfilter(1,1,1,0,0,0,0,0) and you will see the effect of more quantisation ... Image gets more blocky means details are deleted Q value should flew up to the sky

Lets see what DCTfilter makes seen in case of a Matrix (the same effect)

DCTfilter(1,1,1,1,1,1,0.5,0):
"X" means Let it as it is,"-" means CUT and "/" means cut by half (saying and explaining it in "naive" words/visualisations, cause cracks would hit me now )

X X X X X X / -
X X X X X X / -
X X X X X X / -
X X X X X X / -
X X X X X X / -
X X X X X X / -
X X X X X X / -
X X X X X X / -




DCTfilter(1,1,1,0,0,0,0,0)

X X X - - - - -
X X X - - - - -
X X X - - - - -
X X X - - - - -
X X X - - - - -
X X X - - - - -
X X X - - - - -
X X X - - - - -


And if you see the Frequencies of the DCT Matrix you can assume what happens to the image:


And thats also very risky to let DCTfilter do very much cutting (as you already know), in that case you can go directly to encode at 352x576 cause you will see the more the Quantisation at the collums see from the right on, the more it looks like a just stretched 352x576 encoding real encoded at 704x576 Because you do cut vertical frequencies as you can see in the Matrix above, BUT as we see our Encoding on TV which is line based you wont see it that much. Do open the Very Low Bitrate Matrix of CCE and you see what I mean cause there the last vertcal collums will be cut by "99"

So what does an Encoder do if you let him do his job at a very low bitrate?
He won't respect the defined matrix values any more and does quantisize MORE = Blocks at high Bitrate Scenes



Dialhot, I think thats not the direct answer to your question but ...

I do not trust Bitrateviewer and its Q factor.

I used that to find out how much my maxbitrate decrease will influence the quality at kbit peaks.

But at some encodigs at high bitratepeaks where the Q factor says very very bad, the quality in Vdub or Zoomplayer was perfect, ... no blocks, no whatever. strange

mb1 a Mod at doom9.de did a review/comparison between Pinnacle DVDcopy and DVD2One ..... there he also did a test using Bitrateviewer and its Q factor given afterwards. Same thing bad Q kbit-Peak values but good quality on a real preview.

So I came to the conclusion ... (as you also most times do) trust your eyes, and maybe use this tool after encodings to see where bad quality "could" appear and check these parts using your prefered Softwareplayer to do a preview.

I don't know exactly the name of the Appl. but it could be that that one is called "parseMPEG" which contains an excellent mpeg checking engine: Q factor, vector visualisation, Macroblock matrix effectivity and so on.

Angel got on his site the name of the appl. but the site is down now.

Ill go to doom9.de to find out the name of that wonderful (and very expensive ) appl. in the thread of mb1.

Edit: I went there and looked in the review .... no name of that appl. is mentioned but a screenshot where you can assume what capabilities it gots:

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