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.
CONSERVE POWER
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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