The latest rage in consumer electronics interconnectivity is the plug’n’play installation and configuration of displays, DVD players and other media sources made possible by HDMI (High Definition Multimedia Interface). Nearly 60 million consumer electronics devices sold this year will have HDMI capability, and the number is expected to grow to more than 250 million devices by 2009.
Even though a consumer electronics consortium developed the specification, professionals in the movie industry were the main motivators to include content protection in the HDMI standard. They were alarmed by the impact that peer-to-peer downloading and unauthorized file sharing had on the music industry, and were concerned about the extent of DVD pirating. As a result, creators and distributors sought a method to protect their rights. HDCP (High-bandwidth Digital Copy Protection), developed by Intel, has allayed the Motion Picture Association of America’s (MPAA) pirating concerns and is incorporated in the HDMI specification.
The concern then shifted to consumers who had already purchased HDTV displays without an HDMI interface. Producers and manufacturers wanted to switch over to these new standards, essentially ending analog distribution, but also wanted to avoid disenfranchising a loyal customer base. The solution was an agreement between the producers and manufacturers to delay analog shutoff until 2009, when HDMI will have penetrated the market enough to virtually eliminate the problem of component connectivity.
Bidirectional communication is at the core of HDMI technology. Information exchanged between sending and receiving devices minimizes the need for manual set up; this HMDI “handshake” should automatically negotiate video and audio formats. The information necessary to accomplish this is contained in the EDID (Extended Display Identification Data). The receiving device, usually a display, communicates its format capabilities to the sending device, and the content is sent in the specified format.
HDCP follows a multikey exchange algorithm used by many access control and rights management technologies that confirms authentication every two seconds. Because the authentication process happens so often, replacing a legal device with an illegal copying device is virtually impossible.
Home network connectivity
During the next few years, as DTV receivers and display prices continue to drop, consumers will purchase smaller displays with HDMI capabilities to replace analog televisions throughout their homes. HDMI facilitates distribution of audio and video content to any of these viewing locations.
This is fine now, but as enhanced and interactive DTV data services become more prevalent, the latest HDMI 1.3 specification cannot support these advanced features. Because much of this information, such as program guides, is conveyed in the transport stream PSIP data packets, it is not available downstream from the STB or ATSC receiver.
A downstream HDMI-connected digital television is also not able to provide many iTV features, because this information is contained in transport stream ACAP (Advanced Common Application Platform) or OCAP (Open Cable Applications Platform) packets.
Unfortunately, this means that HDMI will not facilitate tomorrow's home digital network. Will this open the door for Internet-delivered television (IPTV)? All the technology is in place for home distribution using IP. With IP, one wire with sufficient bandwidth can deliver content and interactive features to every network-connected device.
HDMI and device control
In the HDMI interface specification there is a single wire that is dedicated to automated device control. This wire acts as the Consumer Electronics Control (CEC) bus. A device tree is built (via auto-discovery) that maps the interconnection of HDMI media devices. Devices have both a physical address (PA) and logical address (LA).
The device that acts as the master is considered the root device, and is given the base PA of 0000 and LA of 0. PAs increment for each device (0, 1, 2, …), while LAs are derived from the level that a device occupies in the tree. For example, if a digital television is the master and is connected to a DVR, the DVR would have a PA of 1 and an LA of 1000, where 1 signifies that it is one level down and connected to the master. If an STB and DVD player are connected to the DVR, then the STB PA is 2 and LA is 1100. The DVD has a PA of 3 and an LA of 1200. Using this methodology, up to 10 devices can communicate with each other.
Clogging the data pipe
As with most digital media applications, transfer speed is essential. Theoretically, implementation of data services across HDMI using CEC is feasible; however, CEC has a limited data rate of 500b/s or less. An alternative method could be sending data during blanking intervals over HDMI. This would require a mechanism to parse the MPEG transport stream, extract data services packets and distribute them over HDMI to ACAP- or OCAP-capable devices.
HDMI 1.3 can support up to 1440 60p video and the emerging uncompressed Dolby TrueHD and DTS-HD audio formats. Content in these formats is too large to fit down any of the traditional content delivery pipes. This presents Internet and terrestrial broadcasters with a channel capacity problem. Cable and satellite operators have the technological means but would have to dedicate and bond multiple channels together to attain a sufficient aggregate bandwidth. This would reduce the number of DTV services that could be carried and would, in turn, diminish revenue.
Advanced codecs may solve the bandwidth problem, but receiving and presentation devices and content production infrastructures must still support the voluminous data requirements. Despite these roadblocks, the consumer electronics industry is still grappling with the viability of true 1080 60p content.
The evolution of HDMI
Somewhere down the line, there is an opportunity for forward-looking professional broadcast equipment and consumer device manufacturers to address the problem of getting DTV data services over HDMI. To do this, the ATSC, SMPTE, CEA and others need to better coordinate more standards development.
HDMI solves many of the problems inherent in consumer digital media system interconnectivity, but to facilitate the promise of DTV features, it must evolve to include more than just audio and video distribution and simple device control.
The HDMI future, Paul McGoldrick, Broadcast Engineering Magazine, Aug, 2006