MPEG Quality vs. Bit Rate

[timwerx]

I've used UVS for 3 years now and am quite happy with the results it has given. One thing I cannot understand, however, is the correlation between "quality" and "bit rate," which is customizable in the "Make Movie Manager."

I decided to play around and experiment with it. I took a captured DV movie and edited out the commercials, leaving me with a 1-hour 35-minute movie to transcode into MPEG for DVD. For kicks, I set the "quality" setting at 100, and the (variable) bit rate at 5500. The resulting MPG movie is 4.5 GB; in other words, a bit too much for one disc.

So, I'm wondering, what do I crank down? The quality setting? The bit rate? Before I had the quality at 80 and the bit rate at 4000, which left lots of room over for a movie of that length. I know that I can get the desired size by adjusting either one down, but which should take top priority?

I tried to find the answers to this on Ulead's site, but (as usual) the tutorials never seem to cover things to the technical level I'm interested in.

If anyone could clarify this correlation or point me to any online resources, I'd be much obliged.

Thanks.

[GeorgeW]

for sizing properly, focus on the BITRATE (the quality slider will just tell the encoder to take more time anlayzing the source material during the encoding step -- that's why you can move that slider towards Quality or Speed).

Your resulting filesizes will be determined by the chosen bitrate (for video plus all audio tracks, plus subtitles, motion menus, etc...). The bulk being the video, and then audio if you are using lpcm audio (mpeg and ac3 audio will use less space).

Here is a bitrate calculator that will help you determine the best CBR bitrate, or VBR Avergae bitrate:
http://www.videohelp.com/calc.htm

p.s. -- out of personal preference, I try to keep the total used disc space to about 4gb (leaving about .37gb on the table). The dvd5 disc burns from the inner circle towards the outer edges, and the outer edges have been known to become problematic (due to handling, scratches, material degrading, etc...)

[THoff]

The Quality setting controls the amount of time spent on identifying motion vectors. The more time is spent on identifying sections of the image that have simply shifted, the greater the potential output quality. But, as GeorgeW said, it does not affect the size of the file, that's entirely a function of the selected bitrate.