So, the bitrate that we select within DVDA, is that the max, min, or average? (I would assume average.) How does DVDA determine the other two?

And, this may be a rhetorical question, but why did Sony (or SoFo) program DVDA for VBR but not give us the ability to choose all three values?

Rob

So, the bitrate that we select within DVDA, is that the max, min, or average?

The first question is easy: It is the average.

How does DVDA determine the other two? ... why did Sony (or SoFo) program DVDA for VBR but not give us the ability to choose all three values?

I don't know the answer, but I can guess. Here's my guess: Because it doesn't matter. As long as the min and max are within DVD spec legal limits, I don't think it matters much for most practical encoding. I have read many posts about people worrying about setting the max bitrate too high and creating disks that won't play on some players, but I've never seen even one actual experiment to prove this, and the mpeg.org site specifically debunks this.

Most likely, the min and max numbers are the same as the default Vegas min/max, which in the DVD Architect template are 192,000 and 8,000,000 bps.

Here's a link to a document describing DVD spec and maximum bitrates:

mpeg.org

Well the the real difference between CBR and VBR is:

VBR: analizes each video's frame and adjust the best quality for that frame, each frame is analized individualy (this task repeats for all frames in the video) For this reason a video with VBR is more big than a video with CBR.

CBR: no analises each frame, only adjust a value and a quality for all frames in the video (this task repeats for all frames in the video)
For this reason a video with CBR is less big that a video with VBR.

CHANGE VBR TO CBR or viceverse take A LOT TIME in a P4.

Juan

Things I know to be true...

Average bitrate for vbr is theoretically the same size as cbr.

cbr is better than 1-pass vbr at high bitrates, i.e. 8.0 mbps or higher.

2-pass vbr MAY be better than cbr, even at higher bitrates.

This is why I encode in Vegas, not DVDA.

Here's my guess: Because it doesn't matter. As long as the min and max are within DVD spec legal limits, I don't think it matters much for most practical encoding.

Sounds reasonable. I may change the average bitrate when using VBR, but I pretty much never change the default min and max values.

Rob

The way I understand it, encoding using either cbr or vbr results in a video (file) that is the same size. The two factors that determine video size is the length of the video...and the bitrate. Once you determine what you want the bitrate to be, say 8000bps, you then choose how you want to utilize that bitrate.

Think of bitrate like a budget. With cbr, the encoding will be consistant throughout the video...regardless of whether it needs to be as high, or low as set for the best quality. With vbr, scenes with lots of motion, action gets more bitrate budget where it's needed most while scenes with little motion can make do with less bitrate and still maintain quality.

It's kinda like having $1000.00 budget to buy your video gear. With a cbr budget, your tripod and tapes will cost the same as the camera, the money is spread out evenly, whereas with a vbr budget, more of the money goes to where it's needed the most, like the camera while less is 'spent' on the tripod etc.

Doc