Why Space Matters

In the next-generation DVD format war, BluRay's main advantages seem to be disc space, and hypothetically increased studio support, though HD-DVD has still managed to release more movies thus far. Does space matter?  Is 50 GB on a dual layer disc going to provide a better home theater experience than 30 GB on a dual layer disc?   That's what we are here to discuss.

Before you Continue, Dear Reader.

Before you continue, dear reader, we must make some assumptions as to what these next-gen optical disc formats are all about.  "Money for manufacturers and studios" is the first thing to come to mind, but for the consumer the answer must be Better Sound, Better Video, Better Extras, Better Interactive Experience.

Codecs

How much space do the modern codecs take up on those high capacity discs?  This may be the only place on the Internet today where you can see these storage costs side by side:

We do some math to make comparing the numbers easier, for example the good ole Dolby Digital 5.1 bit rate is usually published as "641 kilobit per second" but we turn that into .641 megabit per second.

Space: The Final Frontier

Given the above numbers we can make quite a few observations right off the bat.  If encoded at a full 45mbit/sec two hours of HD video could take up almost 41MB of space.  Yet, we have three hour movies like King Kong on HD-DVD.  No, the rules of math are not special for optical disc formats.  The full bit rate supported by VC-1 is obviously not used to encode King Kong on HD-DVD.  Let's assume they saved some space for extras and used 28GB for the transfer.  Doing the math, they may have used a little over 20 MBit/second if it was video only, and obviously less given the Dolby 5.1 sound track.  Most authoring tools are also able to use different bitrates for different parts of the film, further saving on space.

Without having a working example of a film with "this scene was this bitrate" information, it's very hard to come up with an idea of how much space matters.  On paper, we can quickly see the extra space afforded by standard dual layer BluRay disks becoming an advantage in picture and sound quality. 

It seems that this ought to make BluRay the choice for the Home Theater enthusiast, even if not for the market at large.  I, for one, would like to see the highest bitrate possible used in video encoding, as I will be watching on a 106" screen and flaws may appear to me that are invisible on my buddy's 40" plasma.  I would also like to see as much space left over as possible for high quality audio.

Sources

DTS

Engadget HD

Wikipedia