Downgrading Your iPhone's Video Playback Quality to Save Power


A quick word of caution: the tech-savvy in the audience who demand the absolute best in performance from their video-playing gadgets — namely, the highest number of frames per second — may just want to skip over this next story. The rest of you (yes, even the non-iPhone crowd) may be interested in a relatively simple way researchers at the University of Maryland have found to conserve power (by as much as two-thirds) in these gadgets: reduce said frame rate by about 20%.

According to Gang Qu, one of the lead scientists on the study, people are generally willing to accept some level of "execution failure." Most contemporary digital video, he estimates, plays at a rate of about 30 frames per second; in the past, that number was closer to 24 frames per second for old movies. In other words, he believes that while the quality of video has increased over the last few decades, the demands of typical users have not: "That's about 80 percent. If you can get 80 percent of the frames consistently correct, human beings will not be able to tell you've made mistakes."Qu therefore argues that lowering the decoding standards for digital video — reducing the frames per second by six, for example — would have little effect on most viewers and would actually help lower a device's power consumption. He and his colleagues wrote an algorithm that would impose a series of time limits on the decoding process; were any of these to be exceeded, the decoding would thus be stopped. By tweaking the algorithm, they can even control the desired completion rate.

Previous attempts to lower the decoding rate had relied on an approach known as the "naive approach" — decoding 8 frames in a row and ignoring the next 2 — which, while introducing power savings, didn't effectively distinguish between frames that were hard to decode from those that were easy. The approach adopted by Qu and his colleagues introduced a 54% energy savings over the naive approach. "If you are using the current approach, which is going to keep on decoding everything, 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," said Qu.

Though the researchers caution that their study involved signals not quite identical to video signals — suggesting that video decoding may not yield such drastic results — they argue that their algorithm should still deliver superior energy savings. They do accurately model cell-phone voice decoding, however, meaning that your iPhone's battery life could be dramatically improved by using it (voice communication is almost as big a drain as video playback).

While there are no current plans to commercialize the approach, Qu hopes that the focus on energy conservation in multimedia devices these days will soon draw more corporate interest. "If we got some partners," he explained, "if they have a top engineer trying to work with us, this could be done in half a year." We're sure you iPhone users would appreciate that.

Via ::Technology Review: Saving Power in Handhelds (news website)

See also: ::Guardian's Top 10 Eco-Friendly Gadgets, ::Getting Ready for Earth Day: Save Electricity with Solar Gadgets
Image courtesy of kowitz via flickr