I guess it has to do with dynamic range, I'll try to be brief and keep it straight and simple: given a format's dynamic range, one can go for a mid-high dynamic range soundtrack and keep average levels consistently high while saving some threshold for stuff like explosions, thunder storms and crahes, or go to a full-high dynamic range soundtrack, in such this case average levels will be low but action scenes levels will be thunderous (a good example of this is the DTS soundtrack of Spielberg's War Of The Worlds). My opinion on this soundtrack is that it was done both ways, keeping average levels (scenes with dialogue, ambient noise, busy streets) high, but lowering them down on high impact scenes (car crashes, bombs exploxions...) so they don't distort, that may be the reason why you find level to be incosistent. On soundtracks like this one, action scenes will see dialogue both lowered and masked by high level signals. Dolby Digital took prevision of this by implementing Dialogue Normalization, a set of instructions on the data stream (metadata) that "tells" the decoder to increase or decrease the level of the center channel, where most dialogue comes, depending of the overall level of the soundtrack at a given moment. I wonder if Dialogue Normalization was used on this soundtrack. You can try to compress dynamic range by using Night Mode on your A/V receiver (it uses to have several levels, experiment) or DVD player, this should make levels more consistent. One good example of a full-high dynamic range soundtrack is Star Wars Revenge of The Sith, were average levels are kept low but action scenes make use of full dynamic range with expolsions, laser shots and ships crashing. Mid or low dynamic range soundtrack examples are in general remixes of old films to 5.1.
It's bad encoding and/or Sony is using some anti-piracy scheme that doesn't play well with many combinations of equipment.
If you Google, you'll find several complaints about this disc.
DVDs have sufficient bandwidth so that the dynamic range should *not* be a problem. There is no excuse for such a shabby sounding audio track. Many A/V amps and receivers have a compression mode for "late night" or "apartment" viewing, and they don't sound anywhere near as bad as this soundtrack.
The disparity between the upper and lower extent of the dynamic range of an affected scene will *not* be abated by any small compression of consumer or home theater gear.
What has resulted is a DVD with a shoddy soundtrack that sounds bad to almost anybody, rather than one that can sound really good on better equipment, and pretty good on a TV. There are far too many great sounding DVDs around to conclude that Sony had to make some compromise, and that this particular one sounded good to any of their engineers.
The DVD contains an .exe program that is not normally found on DVDs. As I played my DVD on a Sony player and a Mac, the .exe didn't do anything that I know of. Sony already tried to mess with computers when used to play some Sony copy-guarded CDs with a root-kit installed. They had to back pedal big time when that was made public. So there may be some additional software on the Disk that's causing trouble, as well.
The special features disc (Disc 2) is just fine. In fact, even the trailers on the first disc play perfectly. It's not a limitation of a DVD's dynamic range. It's either a defective disc, or given the aforementioned symptoms, it's very possibly Sony's ARCCoS copy protection.
It's also noticeable during the card game when chips are tossed onto the table. Basically any time there is background music and conversation, and a sudden click or bang happens, the audio is ducked for a few seconds to a much lower level and then slowly returns to where it was. It's super annoying.
I've also been seeing this problem on my home theater system (Denon receiver/Polk speakers). Sound suddenly drops noticeably without any rhyme or reason. I've seen it during the opening scene, and the title sequence. Unfortunately, it's too jarring to continue so I've not watched any further. I've even rented another copy of the disc, and it too had the problem, in the exact same places as my copy.
As a test, I tried playing it on my Windows PC (without installing Sony's software-based player) and the 2.0 track seemed to work fine. So, perhaps it's a problem with the encoding on the 5.1 track.
Maybe the new replacement Casino Royale DVD is offering customers dissatisfied with the original release will be better sonically as well as with DVD playability. See information below, from the Internet Movie Database. --- Sony Recalling New DVDs http://imdb.com/news/sb/2007-04-18 Sony Pictures Home Entertainment has discovered the source of a problem in their recent DVD releases that prevented them from being played on some players, including some manufactured by the consumer electronics division of Sony itself. The company said the problem was caused by an update of its copy-protection system, which it continually updates in order to derail potential hackers. Among the DVD movies affected were the new James Bond film Casino Royale, The Pursuit of Happyness and Stranger Than Fiction. Sony said that anyone who had purchased one of the discs and has experienced problems playing it may receive a replacement disk free of charge by phoning 800-860-2878.