The Future of Blu-ray: Compatibility, Compression, Confusion

By Wesley Fenlon

Speaking with the shepherds of the Blu-ray disc format, we investigate the technical and practical possibilities for physical media as high frame rate and 4K movies start to hit the household.

It's 2009, and the Blu-ray Disc Association has a problem. Hollywood is gaga over 3D. Coraline and Monsters vs. Aliens try to sell families on 3D early in the year, while My Bloody Valentine 3D and The Final Destination grab the teenage market. And then in December, James Cameron's Avatar becomes the box office phenomenon Hollywood expected it to be. Thanks to 3D ticket premiums, the movie goes on to earn $2.7 billion worldwide. But Blu-ray doesn't do 3D...yet. So the Blu-ray Disc Association set out to update the specification for an install base of 10 million households.

"Blu-ray is unique in that it's the first package media format I've worked with--and I've worked with every one since LaserDisc back in 1980s--it's the first one we've had with an adaptable format," says Andy Parsons, a Blu-ray Disc Association spokesperson and Senior VP at Pioneer. "No one changed the CD spec to add functionality. No one changed DVD spec to add functionality. When 3D came along, we said 'we'd like to add 3D. Is it technologically feasible, is it possible?' "

Indeed it was. On December 17, 2009, the day before Avatar opened in the United States, the Blu-ray Disc Association announced it had finalized a specification for Blu-ray 3D. The Disc Association went from investigating the possibility of 3D Blu-ray to releasing that specification in eight months. "That was a world record, I think," adds Parsons. He's proud, and with good reason--it took less than a year to add a new dimension to Blu-rays, something that had never been done with CD or DVD or VHS or LaserDisc.

But now it's three years later, and 3D is still a divisive medium. It no longer has the easy selling power to guarantee a movie like My Bloody Valentine 3D a $100 million box office. On December 12, 2012, Peter Jackson's The Hobbit hit the silver screen, bringing with it the most significant technological advance since Avatar sold the world on 3D. The film was shot and released at 48 frames per second, double the traditional frame rate of a century of cinema.

But this time, there's no new Blu-ray spec waiting to usher in a generation of high frame rate films. And despite the proliferation of 4K TVs at this year's Consumer Electronics Show, there's no specification for 4K Blu-ray, either. There's no doubt that Blu-ray will evolve again to keep up with Hollywood's next big thing. But will it be 4K? Or HFR? Or H.265?

As Parsons explains, adding any of those features to Blu-ray will be a whole lot of work.

Where's my 48 fps Hobbit Blu-ray?

Avatar was huge for 3D, but Cameron didn't have to justify 3D all by his lonesome. In ushering in a new frame rate, The Hobbit doesn't have the same pull that 3D did. A relatively small percentage of theaters actually showed the film at 48 fps, and many viewers had trouble adapting to high frame rate footage (but that's another story). It's not too surprising, then, that we won't be seeing The Hobbit on Blu-ray at 48 fps--at least, not anytime soon.

"If you go in and add something like HFR to the spec, you want to make sure it works," says Parsons." That responsibility lies with the "format extension study task force," which the Blu-ray Disc Association established in 2012. It's a new group, but they're doing the same work that the BDA had to do back in 2009, when it weighed the prospect of 3D Blu-ray: Studying "technical feasibility, market demand evaluation, and impact on the install base." 50 million US households are now equipped with Blu-ray players.

Market demand evaluation is an easy one to figure out, here: One movie won't cut it. But what about technical feasibility? Trickier to diagnose.

HDMI doesn't support 48 fps, and TVs would need a firmware update to properly process the signal anyway.

"[We were able to] make [Blu-ray 3D] in such a way, that it...could play like a 2D disc in a 2D player," Parsons says. "If they had a 2D player it would turn out 2D, if you had a 3D player it would play in 3D...Perhaps we could do something like that with HFR." But, he adds, "Not all studios made 3D discs work that way." Some movie studios--Disney, for example--choose to release their films in combo packs, and those 3D versions won't play on 2D disc players.

If possible, the BDA wants to avoid adding features that will only work on certain players. 3D is, for the most part, backwards compatible. But HFR isn't just a problem for the Blu-ray Disc Association to solve. The current HDMI spec doesn't specify support for 48 fps (it can do 50, which isn't quite the same), and TVs would, best case scenario, need a firmware update to properly process the signal. In other words, even if you got a 48 fps Blu-ray, you might not be able to watch it.

Compatibility is just one headache. Data is another.

"[High frame rate] would require a lot more data, because each frame is different," Parsons says. "You do get some temporal efficiencies, because one frame doesn't look all that different from the next. It's called inter-frame efficiency. I don't know if it's two times data capacity, or 1.8, or 1.6, that's something the techies will have to look at. If you're encoding more efficiently, maybe it would not require more than one disc."

Parsons says they could add more layers to discs, but that would, of course, be a compatibility problem--nobody's Blu-ray player can read a triple-layer disc. 48 fps films would likely have to be split across multiple discs, especially when they're long (the 2D 24 fps Return of the King already takes up two discs, for example).

48 fps could mean up to double the data of 24 fps, but 4K is an even tougher problem. Most studios put their movies out on dual-layer Blu-ray discs for a mere 2,073,600 pixels (1080p resolution). How can they deal with 8,294,400 pixels?

The problem of 4K, the promise of H.265

The road to 2160p is a long one because, well, 4K is a lot of data. Right now, only a ton of compression could fit that on a dual-layer Blu-ray disc, but it's hard to say how much of a problem that really is--movie studios aren't exactly in a rush to put their movies out at 4K, anyway.

"It's kind of a chicken and egg problem," Parsons says. "So, at this point, it's very very early stages of 4K. It just was born, really. Does it make sense economically for [movie studios] to build up a catalog? If people start buying [4K] TVs, it will be incentive for studios to get that content out."

The other side of that argument--why buy a 4K TV when there's no 4K content?--isn't a new problem for the media business, but it's one that always takes time to solve. "Nobody goes out to buy this because it looks cool. They need content to justify that expenditure," Parsons says. (Well, almost nobody. Early adopters with money to burn usually end up doing exactly that, when it comes to new technology.)

"When HDTV was still being brought to market, it was the same way," Parsons continues. "Pioneer introduced the first plasma panel in 1998. It was $25,000. No one could afford to buy that. You could buy a car for that, a nice car. We said 'yeah, we get that, we're not trying to sell to consumers right now.' Broadcast channels didn't really go online until many years later. So in some respects its kind of a repeat of the same thing with 4K. It remains to be seen how fast the uptake will be on that." Coincidentally, Sony's first 4K TV released last year also cost $25,000.

There is, possibly, a solution that doesn't require adding layers to Blu-ray discs to store all those extra pixels of information: H.265, the successor to the video codec that Blu-ray and 80 percent of web video currently uses. In the industry, H.265 is mostly referred to as HEVC, or High Efficiency Video Coding. HEVC received International Telecommunication Union approval on January 25th, and promises more efficient encoding of video, lowering the required bitrate by as much as 50 percent compared to H.264.

With basic math, it's hard to see how 4K could fit on a dual-layer Blu-ray disc. But simple arithmetic isn't the full story.

"That is certainly one possibility of delivering 4K, for example," Parsons said, but he admitted he knew little about the codec--the Blu-ray Disc Association currently has no plans to implement HEVC.

Doing some basic math, it's hard to see how 4K could ever fit on a dual-layer Blu-ray disc. The 4K resolution means quadruple the data of 1080p--even with a 50 percent compression increase with no quality loss, there's a big gap. But simple arithmetic doesn't cover the full story.

A paper on HEVC states "one of the most promising application areas for HEVC is the coding of high-resolution video," which it backs up with tests comparing HEVC to H.264 and older formats. The tests saw bitrate savings as high as 67 percent on higher resolution videos.

Gary Sullivan, a co-chair of the team developing HEVC, doesn't rule out the possibility of H.265 fitting 4K videos onto Blu-ray discs. "To me, it seems like that is quite feasible," he writes in an email. Yes, that would require new Blu-ray players--something the Blu-ray Disc Association is certainly in no hurry to push onto the market--but there is a silver lining. "Regarding backwards compatibility, in practical terms, I think that nearly all products that support HEVC will also support [H.264] AVC," Sullivan writes. "However, they are separate designs, and the HEVC standard does not explicitly require decoders to support the prior standard."

And how does the math work out? "When the pixel count goes up, the necessary bit rate does not go up in direct proportion to the pixel count, because the spatial correlation of the signal increases," Sullivan writes. "Here we have the pixel count going up by a factor of 4, which might make the data rate needed for a given compression codec go up by perhaps a factor of roughly 3 instead of a factor of 4. Maybe less than 3, but that seems like a good guess."

Sullivan estimates that a typical Blu-ray film uses a very high bitrate--around 45 megabits per second--for 1080p video, or "more than what is really needed to deliver good HD quality today without using HEVC." He equates a 45 megabit HEVC bitrate to about a 30 megabit H.264 1080p bitrate. He's not far off from the official Blu-ray specs, which currently dictate a maximum 40 mbps bitrate. "Maybe if you want to put 6 hours of content on the disc instead of just one feature film, things might start to get more challenging, but that seems like plenty for an ordinary movie," he writes.

4K Blu-ray looks to be a long way off, but it's not quite as hopeless as we expected.

4K Blu-ray looks to be a long way off, but it's not quite as hopeless as we expected. Parsons sees it as a more likely solution than web delivery. "People talk about, you could just stream 4K," he says. "Well, not really. If you check out the average bandwidth of the US household being six megabits per second, no way you're going to squeeze that down. Package media is the best way to deliver that."

As a member of the Blu-ray Disc Associations, Parsons obviously has a vested interest in 4K being a selling point for Blu-ray and not, say, Netflix. But he also makes a good point about 4K streaming. The average US household's broadband connection hovers around the 7 mbps mark, which barely cuts it for 1080p streaming, let alone 4K. And streaming won't match the quality of a disc-based media, at least not until networks are much, much more robust.

But streaming has one huge benefit: it works a la carte. If Blu-ray adopts H.265, it affects an install base of 50 million. If Netflix decides to start streaming 4K video, only customers with gigantic fiber connections will take advantage of the feature, while everyone else will happily stick with their 720p streams. For once, early adoption may not cost anything at all.