Mediaset Backing ‘Third Way’ for 3DTV

While the two main commercial requirements for 3DTV standards have been defined within the DVB, covering Frame Compatible (phase 1) and Service Compatible (phase 2) technologies, Italian broadcasters are proposing a third, interim approach that makes Frame Compatible 3D services compatible with 2D televisions. If applied, the result would be that broadcasters can deliver one video stream that can be used for 3D viewing today but which can also present a full frame, upscaled HD picture to non-3D televisions.

The obvious drawback to this approach is that the picture reaching the TV screen is only half-resolution HD. However, the big prize for terrestrial broadcasters from combining 3D and 2D services into the same signal is that they do not have to simulcast.

Having to simulcast SD and HD makes life difficult enough for any terrestrial broadcaster that wants to maintain is position as a prestige content provider. Having to simulcast SD, HD and 3DTV would massively limit their possibilities for 3D television on digital terrestrial, due to bandwidth limitations. Broadcasters want to avoid splitting their audience between different channels, anyway.

Mediaset is one of Europe’s biggest broadcasters with its business divided between free-to-air content and a growing Pay TV business (now accounting for approximately 15% of revenues) called Mediaset Premium. The company is backing the new proposal, which has been outlined by the broadcasting associations HD Forum Italia and DGTVi, and which is listed in the latest version of Italy’s profile specifications document, HD-Book DTT 2.0. The proposal has now been presented to the DVB.

Marco Pellegrinato, Vice Direttore Ricerca e Progettazione Tecnica VIDEOTIME at Mediaset, says the broadcaster recognizes the benefits of 3DTV for consumers but has no plans for linear broadcast services today.

“One of the reasons is that very few people could enjoy 3DTV programmes due to the lack of 3DTV aware iDTV [integrated digital TV] sets,” he says. “Commercially speaking, it is not convenient. There is no critical mass. There is not a large enough customer base to launch a service.”

Mediaset also supports the full-resolution HD/3D service compatible mode that is outlined in the DVB’s phase two commercial requirements but the new proposal inside HD-Book DTT 2.0 could hasten the arrival of 3DTV over digital terrestrial.

“That would give broadcasters a chance to launch a 3DTV compatible channel that can be received by legacy HDTV sets. That maximises channel efficiency in terms of the potential viewer, so it represents an adequate customer base,” Pellegrinato explains.

According to HD Book DTT 2.0, annex M, the interim solution works with 1080i and 720p HDTV but cannot be used with the top-and-bottom Frame Compatible format due to the limited ability of many set-top boxes to perform vertical upscaling.

When the Frame Compatible signal is received by a set-top box connected to a 3D television, the set-top box (or integrated receiver decoder) recognises frame packing information and signals this via HDMI to the television to generate the 3D display. Frame cropping offsets and sample aspect ratio combinations needed for 2D service compatibility also form part of the signal but are ignored.

If the STB is connected to a 2D television, these frame cropping offsets and sample aspect ratio combinations are interpreted and instead it is the frame packing information that is ignored. The set-top box (or integrated receiver/decoder) outputs an upscaled, full frame 2D signal via HDMI to the television. For 2D compatibility, no additional PSI/SI signalling is needed beyond what is already defined for Frame Compatible 3DTV.

The new Frame Compatible 3D with 2D approach does require cropping and upscaling capabilities in HD set-top boxes that exceed the minimum requirements currently defined by DVB.

According to HD Book DTT 2.0, annex M: "Such service compatible modes give service providers the chance to transmit a single service that provides both Frame Compatible plano-stereoscopic 3DTV video and reduced-resolution (halved) HDTV video concurrently, whereas normally HDTV coverage with the same source content would be provided with a separate dedicated HDTV service."

Pellegrinato emphasises that this is only intended as an interim solution while a full-resolution 3DTV Service Compatible mode is developed. The full-resolution service compatible approach works on the basis of delivering a 2D service channel plus an extra Delta Channel that provides the differential between the left eye and right eye views, where this differential generates the ‘depth’. A standard HD television set (not 3D aware) can interpret and decode the 2D service element in isolation, in a standard HDTV frame (1920 x 1080) and render it in full HDTV resolution 2D. Mediaset expects this approach to be available for mass-market use by 2014/2015.

Mediaset is already delivering some 3DTV content, however, and using the digital terrestrial signal to do so, but not as linear broadcasters. As part of its Mediaset Premium service, the company is offering one 3D movie per month that is effectively ‘downloaded’ over-the-air, in what is technically termed datacasting. This is a commercial service, not a trial, and the first such movie was offered to Mediaset Premium subscribers last October.

Italian consumers can buy a Mediaset Premium set-top box (the Tele System TS7500HD) in retail to enjoy the Premium on Demand HD service, which provides a catalogue of 50 movies in any given week. 2D movies are broadcast to the hard disk, as well.

The format for this non-linear 3D content is Frame Compatible (side-by-side) and demonstrates Frame Compatible and 2D compatibility in practice, albeit for non-linear content. The set-top box detects the type of television it is connected to and varies the output accordingly. If it is connected to a 2D TV, it sends out the left side of the image, horizontally upscaled to reach full HD resolution. If the STB is feeding a 3D TV set, it sends out the side-by-side image.

By John Moulding, Videonet