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Raj Rajkumar, director of the Real-Time and Multimedia Systems Laboratory at Carnegie Mellon University, mentions that his colleague John Lehoczky and the University of Wisconsin's Parmesh Ramanathan have investigated approaches similar to Qu's. But he says that Qu's work is "the logical extension of earlier work. I think that what Gang did is very useful." Ramanathan adds that with Qu's approach, "my guess is that there will be considerable savings in power consumption. I think one can save quite a bit."
Indeed, the Maryland researchers' algorithm fared well in simulations, offering a 54 percent energy savings over the naive approach. "If you are using the current approach, which is going to keep on decoding everything," Qu says, "we are going to probably consume only slightly more than one-third of that energy. That means you can probably extend the battery life by three times."
Qu is quick to point out that the researchers' simulations involved signals similar, but not identical, to video signals; real video decoding might not produce such dramatic results. On the other hand, Qu says that more-recent video-coding standards call for frame rates higher than 30 frames per second. That means the decoding rate could drop below 80 percent, saving even more power.
And the simulations do accurately model cell-phone voice decoding. In some handheld devices--notably the iPhone--voice communication is almost as big a battery drain as video playback. Without the handy reference of a near-century of analog movies, however, user tolerance for error in voice is harder to gauge.
Qu says his and his colleagues' power-saving scheme could be implemented in either hardware or software, although in the near term, software would certainly be the cheaper option. He adds that the work has drawn some corporate interest, but that there are no plans to commercialize it at the moment. Nonetheless, "if we got some partners," Qu says, "if they have a top engineer trying to work with us, this could be done in half a year."
Novel pixel arrangement and a dynamic backlight could save power.
Spurred by competitor AMD's rapid success, Intel is shifting its strategy toward more power-efficient microprocessors.
Programmable analog circuits could drastically reduce the power needs and cost of electronics in portable devices.
If Gang Qu’s premise that the loss of 20 percent of presentation frames is undetectable is based on, as he said, “in old movie theaters, they played at 24 frames per second” as opposed to video delivery of 30 fps, it is fatally flawed.
The 24fps presentation rate for film does not throw away any frames since it is the same frame rate the film was recorded (exposed) at. In fact, in some circumstances of presentation certain frames may be projected twice providing an effective frame rate higher than 24 fps.
Film presentation cannot be directly compared to video presentation as he is suggesting. Film is presented as an all points at once per frame, and video is a serial line-by-line painting of the frame. In addition, there is the matter of interlace, which further complicates the issue of “frame rate.” Broadcast NTSC video has a frame rate of 29.97 fps, and a field rate of 59.94 fields per second. And still further there are groupings of four fields denoted as color fields, which carry important color timing information.
In order to save bandwidth when video is delivered with any of the current lossy compression techniques, as the previous poster noted, certain frames become critical in the rebuilding of the video image.
I’m afraid that Gang Qu’s algorithm would precisely target the most important frames in the stream and make a very noticeable mess of the viewing experience.
self-timed logic saves power automatically
Hi,
It's true that a lot of power is consumed running in 'idle time', because video decoders are designed to decode for worst-case conditions. In typical conditions several parts are only used 20% of the time and some maybe 60% of the time.
A video decoder developed with self-timed or asynchronous logic will automatically stop using power when there is no activity. This will save more power than the suggested approach in this article, while still being able to deliver the maximum quality.
Re: self-timed logic saves power automatically
Thanks for your suggestion. on every phone video decode engine (hardware) is power gating once decode is complete. Still we need to look at frame rate, comression techniques, reading the video files from memory and sending to decoder, how it's rendering on the screen and overall video software stack optimization and power gating all devices which aren't used duing play back etc.
Guest (famulla)
Sir
I have used the Apple cell phone. It is excellent, only priced a little high. What I would like to have on this is a void command,"sleep" and it goes to sleep not waiting for nay more time, like minimums set in the phones.
Firozali A.Mulla MBA PhD
Manufacturing in the United States is in trouble. That's bad news not just for the country's economy but for the future of innovation.
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jesup
17 Comments
Not practical - not even close
I'm afraid Qu doesn't understand modern video standards well. This won't work the way he envisions - he should have looked at real video standards before doing his research using non-video analogs.
Real video codecs use a combination of occasional stand-alone i-frames, and a series of predictive frames (p-frames and b-frames). Not decoding a frame will typically cause massive distortion of following (and in some cases preceding) frames, since video compression relies on being able to take advantage of the minimal change from one frame to the next.
I-frames (IDRs) are almost always the most expensive to decode, since by definition are stand-alone - they don't reference any other frames, and so include a lot more data to process. But i-frames are the worst ones to drop; that will mess up the entire sequence until the next i-frame.
You *may* be able to drop the last predicted frames right before the next iframe without distortion, but they're unlikely to be the most power-consuming frames. Dropping those p/b-frames is the only way you can save on power here without major distortion, but that's hardly his algorithm. You can encode video with frames that aren't use to predict later frames - but that reduces compression, and this requires purposeful compression for the target use, in which case you could simply not encode the extra frames in the first place.
So, basically, what Qu did has little to no relevance to the supposed target. It might be relevant with the odd/rare use where there aren't dependencies between one unit of processing and the next (motion-jpeg for example - but why would someone on a wireless device be using those?) He should take an introductory course in video compression, I'm afraid.
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