Hi Stu,
The DVD spec states very clearly what is expected of a DVD disc when it is inserted into a DVD player. Burned DVDs introduce variations that can fall outside of the DVD spec. They do this at a much higher rate than stamped (replicated) discs. Physical variations (does the data surface have the proper reflectivity?), logical variations (is all the information about the disc arranged in the proper order and in the proper place on the disc?) and application variations (are there any bursts of data that exceed the limit for DVD?) are the result of manufacturing issues with blank media, hardware and firmware issues with the DVD burners and authoring/encoding issues with the software that was used to author the disc. Not to mention that writable discs come in at least 4 different flavors: DVD +/- R and DVD +/- RW.
You will have fewer variations from high-quality blank media, fewer variations from name-brand burners that are updated with the latest firmware, and fewer variations from professional-level authoring packages (although system and other software conflicts can ruin the performance of even high-priced authoring software).
Add to that the fact that some DVD players are better than others. Pioneer can charge $1000 for its Elite DVD player, while Magnavox can charge $30 for its cheapest DVD player. What makes the Pioneer worth so much more than the Magnavox? More features. Better workmanship inside. Better error-correction circuitry. Better lasers. Better drive motors. And so on. The Elite will most likely play anything you throw at it, including DVD-Audio discs. The Magnavox might play the Memorex disc that you recorded with the DVD burner that you bought at last week’s swap meet and that you authored with Joe Bob’s free DVD authoring program that you downloaded from spyinyoursoft.com, but then again, it might not.
I know that’s not a one-sentence answer, but the simple fact is that there are too many variables in “homemade” discs to ensure full compatibility with all DVD players. Many of the variables that I mentioned are removed when you have your discs replicated at a masering facility.
-Jeff
The Focal Easy Guide to Adobe Encore DVD 2.0