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Mobile video tackles HD challenge

Posted: 01 Sep 2008 ?? ?Print Version ?Bookmark and Share

Keywords:video? mobile TV? multimedia processors? HDTV?

Imagine designing a cellphone with high definition (HD) video quality for watching TV shows, video clips or movies, recording once-in-a-lifetime family events or even playing console quality 3D games. A dramatic shift is happening in the wireless market, making it possible for designers to bring amazing HD-quality video to mobile devices. Advances have occurred in high-resolution mobile displays. The cost of mobile content storage is dropping rapidly. 3G mobile networks support broadband download speeds. And low-power media processing is improving dramatically. These technology advancements will enable the next generation of sophisticated cellphones and portable media products that leapfrog the capability of today's devices.

For the mobile video market to move beyond the early adopter phase, device manufacturers must push the limits of today's technology and embrace the future of HD mobile multimedia. This includes cellphones that can record and playback HD videos.

Today's grainy, low-resolution cellphone camcorders will be thing of the past. The advanced features available in today's digital still cameras!automatic exposure compensation, optics correction, image stabilization, red eye removal and face detection!will be featured in cellphones to capture high-quality still photos. 3D gaming performance will rival that of dedicated handheld video players. Finally, mobile devices will be able to play back HD video in almost any format and output it to an HDTV via an HDMI interface.

An HD consumer experience is a key component for the future of mobile multimedia. However, this opportunity to significantly alter the landscape of wireless multimedia comes with the difficult task of designing products to meet the stringent performance and power requirements to make mobile HD a reality. To get there, a fundamental shift in low-power multimedia processing must take place. Design engineers must adopt a new standard and consider the possibilities and challenges of HD, along with its processing architecture.

Popular video players and associated codecs are shown. (Click to view full image)

Onset of HD video
With the increase in cellular network bandwidths and the growing adoption of Wi-Fi, more consumers are downloading videos to their cellphones and mobile media players. The Internet serves as a primary source of videos. In January 2008, more than 9.8 billion videos were viewed online in the United States, one-third of them from YouTube. Other sources include video-sharing sites, music video sites and TV networks that offer episodes online.

For consumers to view these videos on their cellphones, mobile multimedia processors will need to recognize and support the many standards in which videos are encoded. The table shows the diversity of video codecs widely used today. Content compatibility will be critical to support the vision of "Any Content, Anywhere." To promote widespread mobile video adoption, users should not have to understand what format or resolution their devices support. Users may not be able to view an HD-encoded video on their cellphones at full HD resolution, but they will expect it to play, and they will want to view it in HD on their TV.

There is a general migration toward the H.264 video standard across many applications because of the improved codec efficiency. This video standard includes a broad set of profiles targeting all types of applications from low-resolution video conferencing to HDTV. For maximum compatibility, mobile devices should support H.264 baseline profile as well as the more compute-intensive main and high profiles, which use higher efficiency content adaptive binary arithmetic coding lossless compression. H.264 high profile provides improved quality for a given bit rate and has been selected as the primary video codec for HD Blu-ray disc.

While H.264 has evolved as the preferred video codec today, the successful mobile multimedia architecture will support future media standards as technology advances. By incorporating a level of software programmability, successful mobile multimedia architectures will support the rapid integration of new features and applications, as well as new and evolving video and audio codecs in the future.

The battery life of a cellphone or mobile media device is an essential consideration when designing for video playback. Decoding high-quality pictures from small file sizes takes a large amount of processing horsepower. For a mobile device to support multiple hours of video playback while preserving battery life, the mobile multimedia processor needs to decode video under 200mW, including graphics memory. A device that is power-efficient and requires only 160mW to decode 720p HD video will enable 6hrs of video playback from a typical 900mA-hr cellphone battery.

When thinking through the various use cases of mobile video playback, it is most likely that users want to view a video both on their cellphones and TVs. To do this, the multimedia processor must include a powerful scaler engine that can simultaneously scale and display images of dramatically different sizes. To cost-effectively support video playback on both analog and HDTVs, the processor should include on-chip analog circuitry to support a composite, S-video or HDMI interface.

Use of HD camcorders
In addition to decoding HD video so users can play it on their cellphones, the future of wireless technology will enable users to record high-quality HD videos with their mobile devices. Some of today's cellphones support video recording. However, it is done at low-resolution QVGA, which produces grainy, low-quality videos. While playing HD videos on a cellphone is a major advancement in the mobile multimedia space, using a mobile device to record videos in HD!far surpassing the quality of QVGA!represents even greater progress for the industry.

When considering the requirements to record a high-quality video with a mobile device, surprisingly enough, the image sensor is not the primary factor. Instead, efficient video encoding and image signal processing (ISP) are the most important considerations. Encoding video on a mobile device requires significantly more processing horsepower than decoding the same video.

A 1Mpixel image sensor can easily capture the 921,600pixels created by an HD 720p image (1,280pixels x 720pixels). The primary challenge is not with the sensor. The difficulty comes with the fact that these 1Mpixel frames must be recorded up to 30 times a second. This equates to a raw data stream of 264Mbit/s. Also, to include advanced features such as image correction, antishake, auto-focusing, denoising and exposure control that are required to produce a high-quality HD video, the ISP pipeline must be fast enough to process this data in real-time. With the proper video encoding and ISP architecture, and using H.264 high profile compression, 720p video can be compressed from an unworkable 264Mbit/s into a manageable 2Mbit/s to 5Mbit/s, which translates to approximately 2Gbyte/hr of recorded material.

Future mobile multimedia devices are expected to include 4Gbyte to 16Gbyte of content storage or more, as flash storage capacity rapidly increases and prices correspondingly decrease. It is feasible to support long HD record times from a storage perspective, as long as HD encoding can be done in power-efficiently.

It is not enough just to manage and compress large amounts of mobile video data!it must be accomplished at low enough power to preserve the battery life of the cellphone. Video encoding with H.264 High Profile with a power optimized multimedia architecture can accomplish this. High-quality HD recording can be achieved at less than 450mW processing power including graphics memory to enable multiple hours of video and audio recording on a cellphone with a standard battery. With this processor power profile, consumers will be able to record up to 3hrs of HD video on their cellphone. Camcorder functionality at HD quality in a cellphone will dramatically boost the level of user-generated content, which will propel adoption of mobile multimedia and further expand the popularity of Web-based video sharing.

- Robert Nalesnik
Senior Director of Marketing
Mobile Platforms Group
Broadcom Corp.

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