Alright, inasmuch as this theme was taken up by a couple of seniors a couple of weeks ago on another thread, I'd like to throw in my two bits on this issue and perhaps get a few concrete answers that I failed to get the last time around here.
I'll ask the following:
a - Is it true that the economy in size that DivX should offer over DVD is of the order of 10-1 for a given 'quality'level? Under the best conditions I can only get a compression of about 3-1 before the artifacts kick in.
b - Are there variables that I ignore that can account for superior compression vs quality ratios from commercial DVD sources as oppposed to Mini DV captures.
c - on the topic of DV captures, what are the relative merits of encoding directly from the nearly pristine DV source to DivX vs transitting via the DVD intermediary step?
d - what on par is the percentage quality one may expect to gain by fine tuning an XviD encode (two-pass, quarter pixel, global motion, etc.)as compared to a straight off the shelf single pass encode?
e - Is de-interlacing a technique that can seriously degrade quality if incorrectly used (to blend or not to blend)?
Having asked the questions, I'll just add in my limited experience (and frustration) in this domain. I've almost exclusively used encoding programs (Pinnacle Studio, Virtualdubmod, AoA ripper, etc.) to attempt to reduce mini DV home movies into a more compact format. My results have been very mixed. To be sure the 1/4 size compacting of the DV into DVD works just fine. Yet I've noticed if I take that one step beyond to the mpeg4 format I can either transform the source DV file straight to mpeg4 in which case the colour and contrast are adequately preserved yet with horrific problems of artefacting, or I can recode via the DVD stage to improve clarity and minimize 'boxing' yet suffer the consequences of reduced contrast, faded colour and a slight tint toward the green end of the spectrum. And regardless of what I do, anything under a bitrate of 2000 produces an encode of such mediocre quality that I wonder if it is simply worth the effort not to just cut another backup DVD.
However, when I see some of the encodes other people have done on commercial movies off of DVDs I admit to being quite impressed. Now granted a lot of those encodes cheat by cropping to the excess, such that a 1500mb movie in a widescreen format would translate to nearly double that in a 4/3 (5/4) format with the same quality. Still, those encodes nearly always seem clear and crisp with hardly an artefact to be seen. The only possible major variable that I can detect is that those tight movie encodes are invariably far inferior in resolution to that of the DVD format (e.g. 640x or even 520x). Yet, the couple of times I've tried going beneath the DVD 720x threshold, I got just that...beneath DVD quality. And the two-pass route everyone seems to tout has never improved things much form me more than 10-15% to boot.
In short, is there a fundamental difference in approach that I should be using that has escaped until now. Or is in fact 3-1 compression as good as I should expect. Perhaps, I'd been overrating the prowess of DivX tech all along. Thanks to anyone with any thoughts on all this.
