CQ_VBR = Can u explain what the "CQ" part means?

[Blacklotus]

here's the question

if i have a video and i set the encoding in TMPGenc to CQ_VBR with a bit rate of say 1500 and "quality of 70"
how will it differ from the same setting but with 100 quality (yes, i know its larger, but by how much extactly and what does the quality setting do? makes the average bitrate higher? what?

[Vejita-sama]

Take a look at:

http://www.vcdhelp.com/tmpgencexplained.htm

It's Constant Quaility Variable bitrate (CQ_VBR).

[Blacklotus]

Yes, I am quite aware of that explanation, but i am wondering what the difference is between quality 70 and say 100 in terms of how it calculates the bitrate. does it just make the bitrate the max all the time? or what? what is an IDEAL setting for best quality for the file size.

[Scumbag]

In essence, after about CQ of 75, TMPG starts deciding that the requisite bitrate is at the limit of SVCD spec - so that the effect is that there is no difference between a MPEG with an upper limit of 2600 (approx) and a CQ of 80 or 100.

Only if you go outside of SVCD spec in terms of the upper rate will the higher CQ values have any effect.

For me, the best tradeoff between speed and quality is to use 2-pass VBR calculating the avg bitrate via the calculator you can find here, and motion search set to high quality.

This will generate a file that fills the available space, and provides the best possible quality for that space (except for use of highest setting on motion search - but that takes vastly longer for minimal improvement IMHO)

My DVD player also plays SVCDs out of spec, so I change the max bitrate when encoding to double the avg. I find this helps in really high action scenes. You have to make a call whether you want to do this yourself - it will lower compatibility.

regards,

jr

[Blacklotus]

Tks Scum.

actually, i am interested in doing this with XVCDs not SVCD so CQ_VBR is my best option (according to the Sefy template) I am just wondering how to calculate the space it will take up AND which quality setting will be the best to use for say a 120 min movie on 2 80 min cds (yes i intend to crank the max bitrate up a bit, say to 1600 or so)

[VidGuy]

That's the issue with CQ - you can't predict in advance how much space. It depends on the amount of action in the movie - so about all you can do is build up a rough idea over time based on experience, and if your video comes out too long, drop the quality level.

[Scumbag]

2-pass VBR is just as applicable to xVCD as xSVCD. You just do it with the MPEG1 encoder rather than the MPEG2 encoder.

I do it when I have an interlaced source (typically an NTSC region 1 DVD) that just looks really crappy when converted to 480x576 and played on my PAL TV.

Taking it to 352x288 seems to de-interlace it and look better.

However, when I want to fit lots on a single CDR I find the best results come from using the CVD specs - namely 352x576 or 352x480. My player accepts an SVCD format disc at both those resolutions.

Dropping the audio to 160 and with an average video bitrate of 1197 in TMPG (1169 * 1.024) fits you 80 mins on an 80 minute CDR with really quite acceptable quality, especially for Disney type animations for the kids, which is what I typically use it for.

jr