How to deliver 3D content

Adrian Pennington looks at the technical implications for broadcasters wanting to offer stereoscopic 3D content.

Broadcasters the world over are launching, planning or investigating launching 3DTV services and those in the region are no exception. Al Jazeera Sport has already aired select matches of the FIFA World Cup in 3D while E-Vision and Du also aired Al Jazeera's 3D feed over their respective cable networks.

Other operators and broadcasters are looking to follow suit, among them OSN and the Abu Dhabi Media Company (ADMC), which is building a new presentation, production and playout facility for sports programming.

All are, of course, subscription-based services since 3D, as with HD a few years ago, is easier to monetise as a pay TV proposition. Indeed, public service or free to air commercial broadcasters still find investment in high-definition channels a challenge to justify.

The contrast is evident in the UK where Sky is set to launch Europe's first 3D channel on October 1, while the BBC is taking a watching brief on the format's emergence and remains uncertain of its value to mainstream programme making.

"Is 3D central to the future of TV or peripheral?" questions Danielle Nagler, the BBC's head of HD and 3D. "There's no answer now or likely in the next couple of years."

The BBC is trialling 3D content and has a variety of R&D projects in the works, including an examination of the under-researched psychological effects of stereoscopy.

Mike Darcey, BSkyB's chief operating officer argues that pay TV businesses can grasp new technologies faster than FTA broadcasters, "since to them it looks like additional cost and doesn't add new monetisation opportunities," he says.

Sky's investment in 3D is a loss leader in the sense that there is more value to be gained by reducing churn with a bundled 3D offer, than in attracting significant new revenue from a separate paid service.

"With HD, we took the view that it was best was to introduce a premier tier and to charge additionally for that, but we are earlier in the development cycle with 3D than we were with HD," says Darcey.

"We are still very much feeling our way, seeing how demand grows and it's too early to see how it can be monetised."

The differing business interests between FTA and pay TV channels directly feeds into the technical considerations of how 3D TV can be rolled out.

There are broadly two possible paths for delivery of 3D broadcast services. The first, with which operators can get services up and running quickly and the one adopted by Sky, Orange, ESPN and DirecTV, is termed Frame Compatible Plano-Stereoscopic.

In this system, the left and right HD images are multiplexed (i.e squeezed either side by side, into a chequerboard pattern or split top/bottom) on leaving the broadcaster into a single HD signal which is decoded back into 3D by the viewer's TV set on reception. This system has the advantage of requiring only that the consumer invest in a new 3D-compatible TV with very little other investment - including crucially no change to the set-top box - required by the broadcaster.

The downside is that by compressing two HD signals into one, the resultant 3D image loses up to half of its original resolution.

Of more concern to FTA broadcasters is that this route denies universal viewing of 3D transmissions. This version cannot be viewed properly on a conventional 2D set (the picture would be hopelessly blurred) and requires broadcasters to operate two separate services (for 2D and 3D), which often necessitates two expensive, bandwidth-intensive satellite transponders.

"Colour television would not have got off the ground if the picture wasn't able to be viewed on legacy black and white sets, and it's a similar situation here," observes Bill Foster, senior technology consultant, Futuresource Consulting.

In the longer term, the industry, including Sky and others, would prefer to move to what's called a Service Compatible format in which the left eye signal is broadcast as a standard MPEG picture while the data for the second eye is derived using the left as reference (this is also called 2D+Delta or 2D+ Difference). Such a system would require new decoders to be built into the set-top box.

Stereoscopic 3D content would, however, be viewable at Full HD resolution and would simply look like a normal image on a 2D set.
"While frame compatible has limitations in terms of the viewing experience (notably resolution), it is a good compromise, allowing broadcasters to get a sense of consumer take-up and build on existing HD infrastructure," says Ian Trow, director of broadcast Solutions, Harmonic.

Both methods do incur a bandwidth overhead, requiring more than a normal 2D broadcast, with the variation largely dependent on the type of content.

"Broadcasters need to service new 3D and legacy 2D viewers; therefore, saving costs by reducing the bandwidth needed is one of the key factors," explains Manuel Gutierrez Novelo, CEO of TD Vision, which invented and patented the 2D+Delta method.

"Instead of using 200% (100% to service 2D and 100% to send frame-compatible 3D), the 2D+Delta method works with around 130%-140% bandwidth," he claims.

However, the move to Full HD 3D channels would require a massive upgrade to infrastructure, beginning with contribution circuits, but eventually encompassing the entire broadcast centre.

"It will be a challenge to manage production of a whole channel, including continuity and commercials, remotely from an OB truck where most 3D events are currently produced," notes Foster.

"You'd want the incoming left and right feeds to be ingested within a stereo-capable broadcast HQ rather than created side by side at the point of capture."

Lukas Kernell, the general manager of thematic channels for the Netherlands-based playout provider Digital Media Centre, part of Cello Media, is tackling these issues head on.

It aired the US Masters Golf tournament in 3D for Dutch cable operator UPC and worked with Orange to broadcast the French Open in 3D. "Although our part of the chain is substantially simpler compared to acquisition and post, there are issues," he says. "Subtitling is an area that requires urgent development, particularly for providers that cater for distribution over multiple territories and in multiple languages. An industry-wide solution for 3D subtitling is essential."

Monitoring will prove another challenge once the transition is made from event-based 3D to a fully fledged consumer proposition.

"Not only do we need to invest in monitoring for 24/7 transmission, but we also need to know what are we monitoring," says Kernell. "Clients will expect a certain quality level, but how can we measure that? A lot of work needs putting into standards to be able to deliver a product to clients and their customers that fits all expectations."

Standards are essential to grow the global 3D market - not least because CE manufacturers of Blu-ray discs and players, PVRs and TVs need unified specifications to build to.

In June, Europe's DVB Project agreed the commercial requirements for Frame Compatible stereo TV and it has begun to consider a set of similar specifications for Service Compatible modes.

Dovetailing with its work is the SMPTE's development of a file format needed for producing and transporting 3D TV in the studio. Meanwhile, the HDMI consortium has agreed formats for inputs to 3D displays with the introduction of HDMI v1.4a. The 3D@Home consortium is seeking to get display manufacturers to agree to an interoperable shutter glass signalling system.

Further generations of technology will see the introduction of auto-stereoscopic (no glasses) displays, which work by transmitting multiple stereo-pairs rather than a single stereo pair. Another generation yet may involve recording a continuous object wave passing through a given area.

With that, we're into the realm of in home holographic displays. Which could be half a century or more away. Even the most far sighted broadcast engineers don't have that on their radar.