|Originally posted by Oliver Klohs
you chose your words very carefully, but do you really think that with "normal" movie material it would be possible to differentiate between 15 and 22 mbps when the transfer is carefully done with variable bitrate ?
I do not think there is a need to go above 15 Mbit/sec. Indeed, I think discs can look superb at even lower average data rates. Before folks attempt some bodily harm on me, let me explain :-):
DVDs are not encoded like web video or what consumers use to encode video. The tools are sophisticated and use multi-pass encoding. The video is first automatically encoded at a (variable) data rate that is somewhat lower than the amount of space needed. Then an experienced operator will examine the output scene by scene, and carefully up the data rate on fames that look suboptimal. This process substantially improves the quality, yet the overall data rate only increase by a few percentage points. Reason is that movies have comparatively little difficult content. Most of the movie is slower moving, easier to encode content.
Another reason the above works effectively is that HD-DVD has a peak rate of 30 Mbit/sec. This means one can let a difficult scene use such a high rate and as long this doesn't last minutes non-stop, the overall movie size does not change significantly. 30 Mbit/sec will produce awesome quality with a codec like VC-1.
Assuming the operator knows what he or she is doing, the resulting quality of the above process should be indistinguishable from the original to even experienced viewers.
So yes, I believe 15 Mbit/sec is more than enough and actual discs (regardless of whether they are BD or HD-DVD) may even use lower data rate when using advanced codecs such as VC-1.
Is there a case where you need higher bit rate? Sure, basketball scenes come to mind. Assuming you are encoding 90 minutes of camera pans left and right with no close ups, and want to be able to count the hairs in each audience member, you may need more than 15 Mbit. My sense again is that regardless of format, no one is going to care about this scenario :).