Electronic Design

Success In Portable Video Starts With A Balanced Design

Designers of the latest multimedia marvels face a slew of seemingly conflicting requirements, such as size, resolution, and power.

Planning to design a portable streaming-video product? Be prepared, because several design challenges stand in the way. The wide selection of hardware and software that’s available may seem like an advantage, but sorting through those choices can be daunting.

Today, designers have to balance a number of factors— increased memory capacity, greater processing power, wider networking bandwidths, display type, and power-supply architecture— as they tailor their designs for specific applications (Fig. 1). Beyond the balancing act, they must make these components fit together seamlessly, minimize development costs, and expedite time-to-market.

These demands grow more challenging as DVD players, iPods, nanoPods, 3.5G and 4G phones, iPhones, etc., look to add or enhance streaming-video capability. For example, tiny mobile phones with 2-in. screens can now handle streaming video.

Naturally, media-content service providers are anxious to cash in on these opportunities. Several companies offer services that stream video to mobile devices in addition to their IPTV services, which stream video to the home.

Still, designers have to figure out how to manage and display incoming video streams from multiple sources. Moreover, issues like video compression, decompression, coding, decoding, video degradation, jitter, digitization, codecs, streaming methods, and network transports will all affect video quality, user satisfaction, and the product’s ultimate success.

Of all the issues crucial to portable video design, the processor and the software framework reign supreme. On the one hand, the processor must be powerful enough to satisfy performance demands. On the other, it must be able to operate within a software framework that reduces development time as well as reliance on third-party development tools and intellectual property (IP).

Another two-sided situation involves memory: The processor has to support large amounts of memory with minimum impact on the processor’s performance and programming complexity. But it can’t impose a large burden on the power supply, or the user’s viewing time will be short-lived.

Designers of these mobile devices can choose from generalpurpose processors, DSPs, media processors, ASICs with customizable cores, and application-specific standard products (ASSPs). They can even use FPGAs to configure a processor for a portable video product.

“Software compatibility is a big design issue,” says Greg Mar, worldwide technology manager for Texas Instruments’ DaVinci application program interface (API). “You need the latest processors that can enable digital video and have the flexibility to meet different requirements.”

Mar points to the TI DaVinci DM355 processors, which feature lots of processing power for less than $10 each in OEM lots, as an example (Fig. 2). “A design engineer needs software that can work ‘out of the box’ and support an operating system of choice,” he says. “Designers don’t need to relearn what they already know. Working with the right development platform is the key.”

TI’s OMAP3525 and OMAP3530 use DaVinci technology for DSP video-centric portable applications. “The DaVinci and OMAP platforms are flexible enough to allow the user a choice of display, be it internal to the product or external to a TV set,” says Kevin Hawkins, TI’s OMAP marketing manger.

The DaVinci and OMAP platforms are based on the superscalar, 600-MHz, ARM Cortex-A8 core, which has four times the processing power of 300-MHz ARM9 devices. The ARM is a 32-bit RISC core and is the most widely used processor in embedded systems found in portable video products. Marvell’s XScale processor family also uses this core.

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Meanwhile, ARM RealView Development Suite 3.1 Professional tools target use in ARM’s cores for mobile-phone multimedia products. ARM itself has demonstrated prototype mobile multimedia phones based on its processors with Google’s Android operating system. The OS may pave the way for Google’s Open Handset Alliance, a group of mobile and technology leaders who share the vision of changing the mobile experience for consumers.

The ARM core’s popularity is evidenced by the number of companies allying their products with it. Samsung, for example, sampled a mobile application processor that combines an ARM 667-MHz core in mobile-phone multimedia products.

Many IC chip manufacturers offer powerful supporting chips for multimedia processors. For instance, the STn8815 Nomadik multimedia processor engine from STMicroelectonics adds the Linux operating system to Trolltech’s WQtopia application environment.

Configuration flexibility and scalability are very important qualities in a processor, particularly in processors with a multicore architecture. The VRaptor multicore from ARC International scales to meet high-definition median processing requirements (Fig. 3). It supports multiple ARC-configurable CPUs with media extensions, multiple vectorized 128-bit single-instruction multiple-data (SIMD) processors, high-performance streaming I/O, and domain-specific accelerators.

Choosing a software operating system certainly has a major impact on design considerations. It also affects the likelihood of third-party applications. And, it can influence the product’s overall cost in terms of software investment and the choice of a processor.

The right software development environment can go a long way toward making a designer’s job easier. Environments that integrate processors, development tools, software, and systems expertise enable designers to work at a high level of system abstraction. Linux and Microsoft’s Windows Mobile platform are the two primary players. Thanks to its iPod and iPhone, Apple is key as well, though it doesn’t allow third-party participation in its core IP technology.

Though it’s based on proprietary software, Microsoft’s Mobile platform brings a lot to the table. It is easy to use, supports many industry standards, and provides substantial support for multimedia content. On the flip side, it involves higher licensing costs and sacrifices flexibility for customization and differentiation.

Linux’s future looks bright because it is open-source software. The use of a commercial Linux operation system can streamline software development. Commercial Linux-based packages are available from companies like Monta Vista Software and Wind River Systems (Fig. 4).

The newest addition building on the Linux kernel is the aforementioned Android operating system from Google. Texas Instruments, Qualcomm, and others have showed off early implementations of the Android operating system. The newest product manifestation of Android is Google’s Googlephone.

Digital rights management (DRM) is another major issue. DRM is a layer of security that protects the digital audio and video content from illegal use or infringement by others on copyrighted DRM schemes. It can limit how, when, and where a user can reproduce audio/video content media. DRM, which is generally implemented before the content is encoded when data rates are lower, is easier to use than after encoding.

Microsoft’s Vista operating system employs DRM software. Its protected-video- path (PVP) system can prevent DRMrestricted content from being used while unsigned software is running. It can also encrypt information transmitted to a display or a graphics card, making it more difficult to use unauthorized media content.

More high-performance video codecs are emerging for media-centric portable products. The latest, like the MPEG-4 codec, enables a range of new products and services. Scalable, portable video “jukeboxes” now on the market can handle broadcast-quality streaming video. And, as with anything else, backward-compatibility is very important. Does an MPEG-4 codec, for example, support MPEG-3 and MPEG-2 codecs?

The driving force behind high-definition streaming video is the Advanced Video Codec High Definition (AVCHD) standard. In 2006, Sony and Panasonic introduced this high-definition recording format, which uses an MPEG-4 AVC (H.264) video codec. It can take advantage of various storage media, including 8-cm recordable DVD discs, a hard disk, or flash-memory cards. The format competes with other handheld video-camerarecording formats, particularly HDV and MiniDV.

H.264 video codecs can provide more than twice the compression ratio of the older MPEG-2 codecs. They deliver MPEG- 2-quality video recording, but in less space. Fujitsu Microelectronics America, Algo Embedded Systems Pvt. Ltd., Silicon Hive B.V., W&W Communications, and Mobilygen all produce H.264 codecs.

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However, H.264 is not for everyone. Editing and converting these files eats up a good amount of memory and processing resources. Decoding and re-encoding AVC is much more resource-intensive than similar processing on an MPEG-2 codec.

Furthermore, AVCHD employs long- GOP (group of pictures) frame storage. While space-efficient, this method introduces challenges into the editing and decoding of material. (GOPs are individual frames of pictures that are grouped together and played back so the viewer registers the video’s spatial motion.) Yet, similar to the burden MPEG-2 placed on home PCs at the outset (even needing special PCI decoder cards), AVC’s challenges will be overcome with time, especially with multicore CPUs.

Various support tools for codecs are available, such as the Hantro 8190 multiformat register-transfer-level (RTL) video decoder from ON2 Technologies. The company uses ARM’s NEON processor to optimize the performance of several ON2 video software codecs.

It’s important to understand that a compression standard defines only how to decode a compressed stream. It doesn’t define how the encoding is to be done. Thus, two implementations of the same standard will not return the same compression ratio or the same image quality, nor will they constrain the bit rate with the same limits.

In general, portable video products like advanced mobile phones use two kinds of memory: volatile and nonvolatile. The former stores data during operation, while the latter, which is primarily some kind of flash, typically stores the operating system and applications code.

Mobile RAM should be used for portable video products that handle multiple complex functions. In this arena, processing power, flexibility, speed, density, and bandwidth are prime requisites. In fact, dual-data-rate (DDR) versions of mobile RAM will prove even better.

To meet the low-cost and small-size requirements of portable video products, a number of designers have turned to code shadowing. In this case, code is stored in a lower-cost NAND flash memory. During startup, the code is loaded from the NAND memory into the volatile memory, which then executes it. Although this results in slightly longer boot-up times, it does speed overall operation.

Power is a scarce resource in portable video products, particularly when they’re battery-operated. Choosing a powerful processor that can deliver high-definition streaming video without dissipating large amounts of power can be very challenging. Fortunately, this area is getting a much-needed boost thanks to several technology advances.

According to Nvidia, its APX 2500 offers the lowest powerdissipation, high-definition computing on a chip (Fig. 5). It delivers around 10 hours of 720p high-definition video on connected Windows Mobile phones.

Designers also can minimize power consumption by using circuit components like video amplifiers designed for low-voltage operation. Instead of the usual 3.3 V, the MAX9509 video amplifier IC developed by Maxim Integrated Products operates from just 1.8 V. It reduces power consumption by more than 75% versus other typical video amplifier ICs, according to the company.

Maxim credits its Direct- Drive technology for this advance. Further power is saved because the amplifier turns on only when an input signal is present but the load is disconnected, such as when an output video jack gets unplugged from a portable media product. Once the load is reconnected, the amplifier turns on.

Power can also be saved by choosing the right display. Active-matrix LCDs are the most common type of display in portable video players. Full-color streaming-video LCDs require white LED backlighting that must be very efficient. Typically, this can be achieved via LED arrays.

Now emerging, organic LEDs (OLEDs) require no backlighting and offer lower power dissipation. OLEDs are also more reliable, and they weigh less. Moreover, they deliver good image quality and contrast levels, and yet they can be produced using less-costly processing methods. But to be fully competitive with LCDs, more work needs to be done.

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Sony has exhibited a flexible prototype OLED for portable devices, offering a 2.5- in. diagonal. This display is just 0.3 mm thick, and it can show 16.8 million colors at a resolution of 120 by 160 pixels. It’s based on depositing thin-film transistors (TFTs) directly onto a plastic substrate.

Considering all of the other recent advances in portable video, today’s displays still leave something to be desired. Consumers aren’t likely to enjoy watching feature-length movies or TV shows on such tiny screens for lengthy periods of time. Instead, today’s consumers want to share their media with friends and family via large-screen displays (e.g., TV). In addition to a more pleasant viewing experience, this transfer also reduces the portable device’s power consumption.

The best transfer method is through a high-definition media interface (HDMI) connection. But HDMI transmitters tend to be power-hungry, making them difficult to use in battery-powered applications.

Bucking that trend is a low-power HDMI transmitter from Analog Devices dubbed the ADV7520NK. According to ADI, the device’s active power dissipation is more than half as much as other devices on the market, and its 18-µW standby power consumption is less than 25% of competitive devices.

Finally, video technology for portable media devices is very dynamic, so it’s tough to accurately assess where things will stand in even a year or two. Consider this year’s International Consumer Electronics Show, held in January in Las Vegas, where LG Electronics showed off its Mobile Pedestrian Handhelds (MPHs) while Samsung unveiled its Advanced VSB devices.

These products are prototypes of portable video products that may come out within a year. They’re designed to receive U.S. TV broadcasts. Yet each employs a different decoding method to modify the broadcast signal for reception by mobile phones and other portable media devices.

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