I was also curious as to what use the extra 50GB could be put to, so I wondered about what a max-bitrate encoding would take. Basically a BD superbit type concept.
This has the data transfer rate numbers for BD:
Blu-ray.com - Blu-ray FAQ.
The maximum bitrate for BD A/V is 54Mbps, but only 40Mbps of that can be used for video. The rest would, I assume, be mainly for audio tracks. So, I ran two sets of numbers, the first assuming 40Mbps video and just 2Mbps for audio, and the other using the entire available bandwidth. The results for the first case is that we have about 79 minutes per layer, and in the second case we have about 61 minutes per layer.
Going to the perennial long-movie example of LotR:RotK-EE (252 minutes), we see that it will probably fit snugly in 4-layers if it maxes out the video bandwidth available along with some lossless audio tracks. Granted, an intermission between disks is probably not a bad idea in that example, but I wouldn't complain about it all being on a single (4-layer) disk either. I could also image a more common 2.5-3hr movie with extras fitting on a 4-layer disk without any compromises to the movie.
Of course, in most cases, I'd expect that the same content would end up being fit onto a dual-layer disk by just scaling the A/V bitrate down as necessary. But, I can still hope that at least some films might want to go the max-quality route.
Then there's also the question of whether one 4-layer disk might be cheaper to manufacture, package, and ship, compared to two 2-layer disks. I honestly don't know the answer to that, but I could imagine it going either way.
-- Dave
