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Memory cards support portable video

Posted: 16 May 2003 ?? ?Print Version ?Bookmark and Share

Keywords:memory card? pda? wireless multimedia? pcmcia? compact flash?

Wireless multimedia relies on complex video software/server technology, which in turn relies on complex processing to generate streaming video and audio. One product category that will clearly become wireless multimedia-capable is the PDA. To create a PDA-based system that is capable of good-quality two-way video communication will take enhancements to the computing capabilities of the system.

One approach to delivering this additional performance is to take advantage of the ubiquitous small-form-factor interface standards such as the PCMCIA formats and Compact Flash, which the latest generation of PDAs support.

A big challenge in delivering a compelling product solution is the limitation of these interfaces when it comes to the data bandwidth requirements of large-resolution motion images. However, advances in video data compression and decompression promise to alleviate this problem partly or completely.

Unfortunately, video codecs such as MPEG-4 are developed for processors that cannot deliver the combination of quality, cost and performance demanded in a mass-market solution. Consequently, the nature of the challenge logically shifts to accelerating the use of codecs in more-sophisticated processors.

Why is the delivery of multimedia services on a wirelessly connected Internet-centric computing appliance such a difficult problem? And what can be done to solve it?

While a wirelessly connected PDA has a screen to view images, as well as speakers and microphones to reproduce and capture audio, it does not come with a video-input capture capability. Since these devices are designed to be cost-effective, they use the most economical processor they can. The problem is that to do two-way streaming video at a market-acceptable quality requires processor power and compression/decompression hardware and software.

When Media Works looked at ways to solve the problem of MPEG-4 video capture, transmission and playback on current PDA devices, our first step was to develop the missing video-input capture capability.

This was accomplished by developing a PCMCIA-based VGA-resolution camera. We chose a sensor that provided sufficient frame rate and image size. Although a PDA cannot display a VGA image, the user may want to wirelessly send the image over the Internet to a PC user who has the capability to view it. PCMCIA was the chosen format just for ease of development, but Compact Flash is another target. The initial architecture passed the full image data over the PCMCIA bus to the PDA, where software was used for encoding outgoing images and decoding incoming ones.

The initial results provided acceptable 7fps to 12fps QCIF (176-by-144 pixels) images - a view of what the local user sees and an image of what is being sent to the local user. These results were acceptable as a proof of concept, but the image size needed to be increased to satisfy the transmission to a PC. Also, the frame rate had to be faster to make the video more fluid.

Digging up solutions

The next generation needed architectural changes to solve these issues. Since we are looking at augmenting PDAs without video capability, we still needed to provide a PCMCIA- or CompactFlash-based VGA-capable camera. However, to increase performance, the bus bottleneck and compute performance limitations needed to be overcome.

This is accomplished by having the encoder reside on the camera side of the interface. Depending on the image sequence, the encoded version can be less than one-tenth the data rate of the original.

The encoding is the more computationally intensive task since encoding requires partial decoding capabilities. Our solution was to develop an encoder for the camera leveraging configurable-processor technology. This new architecture also lends itself to the next generation of products that will add wireless capability to the camera. The decoding will remain in software on the PDA. With this approach, we believe that CIF-resolution images at 30fps and VGA images at greater than 20fps are possible on a wireless PDA.

- Larry Przybylski

Chief Software Engineer

Media Works Technology Corp.

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