Are You HD-Ready?


Established Member
19 June 2006

eremiah Golston and Gene Frantz
Texas Instruments High-definition (HD) video is about to arrive in a big way, as you can see by walking through any appliance store, where big signs announce that new TV sets are HDTV-ready or HDTV-compatible. With the lure of wider screens and higher resolutions fueling demand, and the supporting technology in place or being deployed, it is time for video system designers to investigate fully the issues of implementing HD. The market is getting ready for HD products, but are you as a designer HD-ready?
The Extent of HD
The first thing to acknowledge is that not all digital TV (DTV) is HDTV, and not all HD video is TV. There are standard-definition (SD) formats that digitally approximate traditional analog TV images, and low-definition (LD) formats for handheld screens and windowed images, as well as several HD formats for large screens. The right display for a given digital video application may not be the 1080i60 (1920×1080 at 60 interlaced fields per second) format that North American broadcasters are generally deploying for HDTV. This format, with its 16:9 wide-screen aspect ratio replacing the traditional 4:3, looks wonderful on a 40-inch screen or larger. But on a small screen for, say, viewing in the back seat of a car, it is difficult to see any difference in quality between HD and SD.
And HDTV is only the beginning, or perhaps it would be better to say, it is only an important application for HD, which includes a variety of applications for stored, streaming and live video, as well as broadcast television. Videoconferencing may find an HD format such as 720p30 (1280×720 at 30 progressive frames per second) satisfactory, while the same resolution with twice the frame rate (720p60) may provide the best solution for fast motion and non-stop action of sportscasts. Other formats may be more desirable for other types of applications or for viewing on unconventional displays such as wide computer monitors.
More Than Meets the Eye
Other factors besides display are involved, too. HD products generally package surround sound along with a high-resolution display, and designers should not ignore the advantages of advanced audio. Great sound can make a so-so image seem better, while the effect of a great image is diminished by inadequate sound. The system’s audio requirements are at least as important as its video requirements.
Digital video systems have to process not only the display output, but also the compressed signal input. Video compression/decompression (codec) algorithms are almost always lossy, meaning that the decompressed image is less well defined than the uncompressed original. Pushing compression beyond the ~60:1 ratio normally supported by the Main Profile of H.264/MPEG-4 AVC risks revealing flaws in the image that show up much better on HD displays. With excessively high levels of compression, it may be better to choose a smaller display and lower-resolution format.
Higher compression comes at a price, though that price may be essential to HD systems, where the sheer volume of data puts bandwidth and storage at a premium. 1080i60 video has 6× the amount of data as decompressed SD video, so in raw terms the system has to provide 6× the processing throughput and memory. MPEG-4 and other advanced codecs demand higher performance than older codecs, pushing processing and memory requirements even farther. Clearly, HD is more expensive to implement than SD. On the other hand, semiconductor costs fall quickly, so designers must make one more tradeoff: is it better to pay to implement HD now, or stay with SD for one or two product generations until component prices drop and market demand rises?
Successful HD systems may have to support a variety of audio and video codecs. A transition from MPEG-2 to MPEG-4 is upcoming for video broadcast and distribution, and competing standards such as WMV9/VC-1 and China’s AVS will also claim their share of applications. Systems such as set-top boxes (STBs) may have to deal dynamically with any number of codecs and codec variations, as well as interface to entertainment and gaming consoles and transcode video for home computer networks. High performance and programming flexibility are the keys to addressing these diverse video market trends.
Selecting a Processing Platform
A highly integrated digital signal processor (DSP) is designed to provide the high level of real-time performance needed for codecs and HD-scale data streams. If the processor also integrates a RISC core, it can simplify programming and efficiently partition performance between the DSP for signal processing and the RISC for control, communications and applications. Processor architecture can also offset some of the additional cost of implementing HD by integrating additional memory, advanced multichannel DMA, essential high-speed communications, and video peripherals that support camera inputs at the front end and display outputs at the back end. Programmability supplies the flexibility needed to support a variety of codec and display standards, and it also allows the system to be scaled readily to accommodate new functionality or address new market segments. When the processing technology includes a comprehensive, easy-to-use software platform with audio-video application programming interfaces (APIs) and standard codec algorithms, it can simplify development and help save time to market.
An example of media processing hardware and software with these features is DaVinci™ technology from Texas Instruments. In addition to providing the hardware features described above, DaVinci technology also abstracts the complexity of programming the underlying hardware for greater versatility and ease of use. The software architecture allows application developers to program only the RISC, and essential video modules including peripheral drivers, memory management and codecs have already been created. With support from a variety of standard development tools and innovative techniques for faster debugging, the DaVinci open platform can cut video system development time by more than half.
Facing the HD Challenges
System developers have to understand the design challenges that come with the new high-end video technology. Even with its variety of formats, HD may not be right for all digital video products. When it is, though, designers need to consider the additional performance and cost requirements, the balance between audio and video, and the versatility of the system for supporting various codecs, displays, interfaces and applications. The real question is not how to implement HD, but how to achieve the best possible display for the system, given the bandwidth and storage constraints and the target manufacturing cost. When you know the answer to that question, you’ll be HD-ready.
Jeremiah Golston
Distinguished Member Technical Staff