Optimizing DVD - Causing Degradation?

alastairbrown wrote on 7/31/2003, 5:50 AM
This follows on to a problem I have noted with a deteriaration in text quality on an 16 min Autolooping DVD I made. To make it Autoloop I set the pre-rendered MPEG as the background image on my otherwise empty menu. When I went to make disc it warned me that my file size was 1.2Gb which was bigger than the max 1Gb allowed. Used the optimize feature and the resulting disc had very poor text quality compared to the original mpeg. Even a virtually identical disc I made on my old Pinnacle Studio 8 setup was better.

My question is, am I right in saying that optimizing the disc will simply re-encode the mpeg at a lower bit-rate resulting in the reduced quality I am seeing. Can't imagine re-rendering an already rendered MPEG is the best thing for it. Must be asking for trouble? Would I be better to let it optimize the original avi?

Comments

BillyBoy wrote on 7/31/2003, 8:56 AM
It would be better to know up front how big your project is going to be and not try to squeeze more on to a single disc that can be held without recompressing. Sorry guys, I just chuckle when I see people post, oh my goodness... I can't get my project on the disc. You got 4.7 GB space, for Pete's sake! I swear, if the capacity of DVD discs were 20GB somebody would be asking hey, how can I get 21GB worth of material on it.

As for your question, if you know up front you're trying to sqeeze more on a disc that it can hold OF COURSE bring in a AVI so you don't recompress and MPEG which is already recompressed. That applies to video. For the audio portion, it isn't that big a deal. Unless you have ears like Spock from Star Trek, you'd be hard pressed to detect the minor change in quality.
jeffcrow wrote on 7/31/2003, 6:36 PM
Optimize is a really bad name for that, because if you slide the bitrate slider to the left, you are cranking up the compression, which will make it look worse. I think they meant you are optimizing the size to fit on the disk. If you slide it to the right, yes you are reducing the compression, but you are forcing it to rerender, and rerendering an already compressed mpg2 file is not optimizing it. Playing with compression under "Optimize" is not a good idea, keep your content well under the limit (or DVDA will "optimize" it automatically, the size that is, not the quality) and let DVDA do the rest.

Like Billyboy said, if you are going to have to increase compression to get something to fit, render it to avi instead of mpg. Otherwise you are taking your original image, which was degraded by encoding it to mpg, then forcing a re-render, which will degrade it more, and then turning up the compression, which degrades it yet again. The avi will prevent 2 of those 3 degrading steps. Better yet, edit it to be shorter, then you eliminate the third step, if it can be edited shorter of course.

So yes, "optimizing DVD" does cause degradation. You are optimizing the length of the content not the quality, (you are doing so by degrading the quality), regardless of which way you slide the slider.
alastairbrown wrote on 8/1/2003, 12:29 AM
Agreed. I re-made my disc without optimizing it and the text is as clear as I'd hoped.

For the record, the max size of a single or all menues is definetely 1Gb which equates to around 15mins of video?

Just so that, in future I know not to make self looping demos any longer.