determining Q of a multi-pass VBR encode

[calyx]

Is there a way I can interpret the Q value for an encode using multi-pass VBR? I know I can open up rebuild.ecl (yeah, I'm just using CCE through DVD-RB) of a project set to 1-pass VBR (OPV) and it displays the Q for each VTS, whereas if you open a multi-pass VBR version of rebuild.ecl it displays the bitrate for each VTS.

I'd like to see if there is some calculation, tool, whatever, in order to put a quantitative descriptor on the quality of each VTS, so that I can compare them easier.

I don't even know if its possible, or even logical, I'm just experimenting with 1-pass VBR in DVD-RB, and for some rather long movies, the Q value is suprisingly low.

I'm going to go ahead and reencode it using OPV and compare them visually, but I'd still like to see how much of a quality difference there is numerically.

Or maybe I'd be better off comparing the actual bitrates for each VTS, but still, one number would be easier :)

[RB]

Originally posted by calyx
Is there a way I can interpret the Q value for an encode using multi-pass VBR? I know I can open up rebuild.ecl (yeah, I'm just using CCE through DVD-RB) of a project set to 1-pass VBR (OPV) and it displays the Q for each VTSThis is just the Q factor specified in the ECL for OPV encode, it is not the actual average quantization factor resulting from the multipass VBR encode. To see the actual average quantization factor, you need to click the "Bit allocation" button in each items settings. Note the "average Q factors" you see there are not the CCE "Q factor" you specify for an OPV encode.

[calyx]

Ahha, I see what you mean.

Let me get a few things straight.

So those "avg. Q factors", those are my actual average quantization factors, correct?

Now I see how I can do this with an AVS that is set to multipass mode, but what about one with the mode set to 1-pass VBR? Since those Q factors displayed without clicking the bit allocation button are just the Q factors specified in the ECL by CCE/DVD-RB, I'd like to be able to view the actual avg. quantization factors & bit allocation for AVS files set to 1-pass as well.

[RB]

Same procedure. But just to be sure, you really can't know the final avg. quantization beforehand. IOW, by performing an OPV encode with "Q 30", you can't know what the resulting "real" quantization factor (displayed after clicking Bit Allocation) will be.

[calyx]

Yeah, that makes sense.

So if I wait until after I do the encode, and then switch the mode from 1-pass to multipass, and then click bit allocation, I will be viewing the actual avg. quantization factor for the 1-pass encode, correct?

And thx for all the insight you've provided, even after doing backups for almost 2 years I'm little more than a hack at this.

[RB]

Originally posted by calyx
So if I wait until after I do the encode, and then switch the mode from 1-pass to multipass, and then click bit allocation, I will be viewing the actual avg. quantization factor for the 1-pass encode, correct? Correct.

[calyx]

Thx for your help RB, I do appeciate it :)