The question sounds like a no-brainer, but please hear me out...

If HD-DVDs and BD's contain 1080 lines of resolution, then they obviously contain 480 lines of resolution. That begs the question: Why can't a DVD player extract (whatever you call it) 480 lines of info from a hi def disc and play it like a DVD?

I'm sure it has to do with programming, but that begs another question: Why didn't the makers of hi def discs design them so that they could play at 480i/480p on DVD players? This would have allowed consumers to buy new hi def discs, play them in SD on their existing DVD players, and then eventually play them in HD when they could afford to buy new equipment to take advantage of 1080i/1080p. (HD DVD combo discs sort of address this, but why do they have to have one side for SD and one for HD?)

The are completely different physical technologies. The laser for DVD is waaayy too wide to read the tiny lines of code on an HD disc of either type. Actually, the physical tech for both HDDVD and BD is essentially identical, only software is truly different.

And there isn't enough space to put both the HD and the DVD on one disc. Unless you do the hybrid dual-sided discs, which do exist. They are called Combo discs, you can find many threads here complaining about them.

That is incorrect.

HD DVD is based on AOD (it actually is AOD renamed to HD DVD after toshiba learned that BD was to be a 50 gig format with 1080p video and lossless audio, they dumped their Dual Layer DVD9 Low Bitrate VC-1 plans and adopted AOD), which is actually an evolution of DVD. Its why there are so many companys that can press HD DVD titles, DVD production lines can be converted to HD DVD, but not blu-ray.

Blu-Ray needs all new lines built from the ground up as it is all new technology. The only thing they share is that they are both using a blue laser to read the discs. Otherwise, they are pretty far off from each other technologically (AOD main strength is ROM discs, BD was designed initially for PC usage, which is why there has been blu-ray burners and discs (BD50 blanks are available already) and why there is hardly anything for HD DVD on this front).

...and Blu-ray was originally a recordable-only single layer format with no advanced video or audio codecs. Who cares? It's history.

Blu-ray and HD DVD have much more in common than not.

Well, Blu-ray isn't all new technology either. It's derived from Sony's own PDD format which was circulated in business circles for professional storage. In fact, Blu-ray is the "consumer" version of what PDD is. Which is another interesting topic in and of itself.

Recycled technology. But Joe's original question was why these new HD formats don't play in standard DVD players. The answer is simple, as given above, which is, different laser wavelength.

Joe, the reason why you don't see much forethought from manufacturers, is because they want you to upgrade to an HD DVD or BD Player. They don't want you to play their HD discs in your older machine. They want you to play them in a new machine. However, you can play SD DVDs in HD DVD players so it's a little consolation.

Well, that's wrong. HD video takes up a lot more space than is available on a dual-layered DVD. For HD content to play on a standard DVD, you'd either have to use a great deal more compression, or the willingness of the consumer to have movies spread over multiple discs.

For example, a dual-layered DVD could hold only 85 minutes of HD video, and that's using one the newer, more efficient codecs. Using the MPEG-2 codec used by existing DVD players, it would hold even less.

That is kind of like asking why a PS2 will not play PS3 games or why an XBox will not play XBox360 games. I mean advancement is advancement - you have to pay to play. I could give you facts like some above, but even if the laser was not different, they would still probably make you buy a new machine - that's the way CEs work.

An HD copy of Star Wars will fit onto a DVD-9. Granted, it has to be compressed with VC-1 with an average bitrate of 13.0 mbps, but it'll fit.

I mean it would fit. Hypothetically.

You're not understanding me. Of course it's more content. But why do you think they designed such a format in the first place. It wasn't because of the good of their hearts. It was to break away completely from older players so you'd have to buy new ones. Truth be told, you could have amazing quality from SD DVDs if only the movie companies would have wanted to do it.

Also, has anyone actually checked the amount of space these movies take up on an HD DVD or BD? Are we actually seeing burned movies running at 20GB on the disc? Because with SD DVD, you'd have a dual layer disc, and theoretically, you'd have about 7.5GB of movie to play with, but more than often, the movie companies only put around 3.5GB of movie content on there.

So, it might be a good idea to check how many GB are actually the movie on a HD DVD and BD disc before we unconditionally say HD DVD and BD would be incompatible. Not saying this would be exclusive, but merely indicative of the movie companies and marketing, and that's just one aspect of this "HD" thing.

I've steered clear of AVS lately (where a lot of the discussions of GB size of discs and everything are) but I seem to remember some of the earlier discs getting to at least 12GB.

It may be worth mentioning that you can watch the new discs on a standard definition TV at 480i/p if you want. Of course you need the new player for reasons mentioned above. There are some people who have 480p projectors that claim there is a noticeable difference between DVD and HD DVD/BD despite the limited resolution.

I still think the intent of the OP's question is being overlooked. The way I read it is, he's thinking of things like PC games, where you can set the resolution lower or higher depending on your graphics card. Laser width issue aside, it seems like a pretty insightful question to me.

Yeah, but DVD players still can't read the disc. The only way to get DVD players to read anything is to put in in DVD format. Which either means a HD DVD/DVD combo disc (one format on each side), or a layered disc with a DVD layer and an HD DVD layer.

Neat idea, but the whole thing would still be an entirely new format. First of all, the disc itself would have to determine how it was being viewed. You couldn't have legacy DVD players do it -- it's not in their specifications. And since the DVD spec calls for MPEG-2 encoding, you couldn't use advanced video codecs like VC-1 or AVC. The space required for such a file would be more than what the DVD spec could accommodate (thus the need for a format with more disc space, requiring either larger discs or, as in the case of HD DVD and Blu-ray, a smaller laser capable of reading more in the same small space).

Someone please correct me on this, but aren't PC games vector-based images which link to different files for things like texture and lighting? Files like that would be quite a bit different (read: much smaller) than the compressed bitmap images of current video codecs.

Currently they can't, no. Again, what I'm getting from the OP's question is why wasn't the hi-def format piggybacked onto the current format so we could do thing like play new PC games on a slightly older PC, just with a bit of a resolution hit.

Are the new codecs that much better at compressing? Or were they just necessary for dealing with such large amounts of data?

Say you wanted to play a game on a DVD-Rom disc in your computer which only has a CD-Rom drive. Would it work?

For that matter, why can't you listen to movie soundtracks off your DVDs on a CD player?

Doesn't work. Different technologies. Not compatible.

Both, actually. Yes, the new codecs can compress more efficiently than MPEG-2. Also, they are practically necessary for achieving good quality and play length on HD DVD at least. BD can get by with MPEG-2 due to higher bandwidth and disc space (with BD-50), and quite a few BDs use MPEG-2, but the new codecs should be encouraged so as to fit more on the discs. We finally have a format that can present something like Lawrence of Arabia on one disc, and I'd be somewhat disappointed if it had to be split up just because they decided to use MPEG-2.

I'm not sure the PC games analogy is a good one considering we're dealing with nearly 10 years of technology advancement between DVD and the new formats. Most adjustments for a game involve the graphics card anyway which is just one part of the system. You couldn't run a modern game on a PC from 10 years ago no matter how you set the detail sliders.

In any case, copy protection enhancement alone would necessitate a new format.

Not what I was asking at all. I'm asking about scaling the resolution, like on PC games, which Drexl addresses in the next post.

I realize a large part of the reason we have the hi-def formats is so the studios can sell us the same product all over again, but it seems to me if something like the OP mentioned had been built into the format in the first place, there might be few more sales to people like, myself, for example. I am happy to sit out this format war until a winner is decided, but if I could play the discs on my current setup, then I might have started buying the advanced format discs and maybe give my format of choice a little extra boost in the war.

The direct equivalent to scaling back your game resolution because you have a crappy monitor/video card is playing an HD DVD/BR on a non-HDTV...it will display just fine. In both cases, you still have to be able to read the media...your old floppy disk drive isn't going to read a CD/DVD game...and your old DVD drive is not going to read a HD DVD/BR.

Not to be aknolly anal, but has anyone actually checked to see how large a file a movie is on an HD disc?

The OP's question was like asking why an LD player couldn't also play DVDs, or even VCDs.

The reason why a DVD player could never play a HD disc is threefold:

1) Different physical structure.

Others have already gone into this aspect, and we seem to be kinda stuck on it. However, just to go over it again, both of the new HD formats use a new, thinner laser wavelength to store more information. However, BD also stores the info at a different depth, which requires a different focal point for the laser. Also, the requirement for a faster bitrate means that the discs spin faster as well.

However, let's say that the discs weren't physically different. In fact, HD DVD spec allows for the use of standard DVD discs to store HD content if wanted:
http://en.wikipedia.org/wiki/HD_DVD#Disc_structure

The physical structure of the disc isn't the only hindrance though, there's also:

2) The information's in a different format.

This includes, but is not just, the new and different codecs for encoding the video and audio. It might even be the same codec as DVD (MPEG2, DD), but at a higher bitrate than the DVD spec allowed for. Or look at DTS HD, which contains a DTS core that matches DVD spec, but a DVD player would have no idea how to extract that core from the DTS HD track. Also, video on HD discs are usually stored progressively; DVD only stores video interlaced. Aside from the codecs, the way it's stored on the disc is slightly different, and the way the menus load and run are different as well.

But let's say that not only are you using a DVD disc, but are using the two familiar DVD video and audio codecs, MPEG and DD, and that they're at the low bitrates needed for DVD compliance (the video would look like sh*t, but let's ignore that for now). The video is also interlaced instead of progressive. Let's even say you master the disc and it's menus and such according to DVD spec. You'd still run into the final, and most notable difference:

3) It's a different resolution

It's basic, but there it is. The OP asked about somehow "extracting" 480i from the 1080p video, but in order to do that, it'd have to recognize that 1080p even exists, and it'd have to be able to process that large resolution first before it could extract anything from it.

DVD players were not designed to process any resolution above 576i. Any resolution higher than that and it'll throw up. Now, this may be an odd thought in the days of upconverting DVD players, but remember that those DVD players are still just processing SD video first and upconverting later. For a PC analogy, think about how nearly any PC can play a youtube clip fullscreen, but to play an HD video you need a lot of processing power, even if you shrink the HD video to a postage-stamp sized window.


Basically, the change in resolution necessitated a format change, in and of itself. The format could've used the same physical disc, same codecs, etc., and because the DVD spec wasn't designed to handle HD video, a DVD player wouldn't be able to play it. Since a new format was needed anyway, the forums that developed the new formats changed other aspects as well to make the full use of the most advanced technology available today.

HD takes about 6 times the space of SD. Even with MPEG4, which is twice as capable as MPEG2, it won't fit on DVD. But that doesn't matter since DVDs have to be MPEG2, that's the specs for DVD. Sure, you could make a player that could read MPEG4 off a DVD as an option, but for Fox or Paramount to make a DVD disc, it must follow the specs to be compatible with all players. You just can't force the size of HD into DVD.

One significant difference between PC games and HD discs is that the PC game itself actually generates the video that the video card has to handle. If the video card can't handle a high resolution, no problem, the game can generate a lower resolution image for the video card to process.

With HD discs, the video image was already generated before being put on the disc, all the player has to do is process that image. The only way for multiple resolutions to be available is to have multiple, fully-generated video streams on the disc itself, which is in essence what a combo DVD/HD DVD disc is.

It couldn't have been built into the DVD format in the first place, because when the DVD format was finalized, the technology to handle HD video on a DVD-sized disc didn't exist yet; at least, not at anything resembling consumer-level affordability.

The thing is, the DVD spec is a strict one, that requires all DVD players to be able to play all DVDs, and all DVDs to work on all DVD players. In theory, a DVD produced today will work on one of the first DVD player produced 10 years ago. Now, in practice, this doesn't always work out, but it works out a hell of a lot better than with PCs. With PCs, a program is not required to be able to work on all PCs that were ever made. Hell, a PC program isn't even required to work on all PCs being made right now. And PCs aren't required to run all existent programs either. We accept it with PC software, but we wouldn't with consumer gear. How would you like it if the latest DVDs didn't work on your DVD player? Or the latest CDs?

Again, that's what combo DVD/HD DVD discs are; they've been around since the introduction of the HD DVD format.

Thanks for all the responses! Now I have to try to explain all of this to my friends and family who are just casual movie watchers and not really into home theater all that much.