A CPU Bound Case: Streaming YouTube Videos

Bandwidth enables new usage models, it's what we saw on the desktop and it's what we're seeing in the mobile phone market as well.  Streaming video to mobile phones is a definite bandwidth consumer, and something that's truly enabled by 3G wireless technologies - but at what cost to battery life?

On the Blackjack we used the YouTube Mobile site (m.youtube.com) with a hack to enable playback on Windows Mobile 5.  We played back the same video over and over again until the battery died.  Unfortunately the longest video we could find on YouTube Mobile that was stressful enough for our test measured around 5.5 minutes, meaning that by the end of the 3+ hour process we were ready to die. 

Things were a bit easier on the iPhone as its YouTube implementation has a larger selection of videos, including our test video which was over 40 minutes long, thus requiring fewer clicks on our part to keep the video looping. 

Our YouTube test is a little misleading when it comes to the iPhone because there's more than one variable being changed here.  When switching between Wi-Fi and EDGE on the iPhone, the YouTube client automatically requests a different quality video depending on what wireless connection you're using.  The stream over Wi-Fi looks absolutely beautiful, while over EDGE you get a much lower bitrate stream that's more reminiscent of what YouTube looks like on the web.  The problem with this is that we're unable to measure the impact of Wi-Fi vs. EDGE alone, as the flipped results show (EDGE outlasting Wi-Fi). 

Looking at the Blackjack results helps us make sense of the iPhone's behavior.  Streaming video from YouTube is predominantly CPU bound, so much that the primary determinant of battery life is the CPU itself, not driving the wireless antennas.  The end result is that while 3G draws more power than EDGE, the difference is around 6% because the CPU is eating the vast majority of the power budget and its role is identical regardless of whether the phone is running in 3G or EDGE mode. 

If we assume that the same CPU bound limitation exists on the iPhone, the fact that while decoding lower quality video the iPhone would last longer makes sense.  Lower quality video means a much lighter load on the iPhone's CPU, thus resulting in longer overall battery life.  In this case, the significant reduction in quality results in an equally significant increase in battery life (37% or close to an extra 1.5 hours). 

Still an Impact while Mostly Idle? The Email Test The Real Shocker: Impact of 3G on Talk Time


View All Comments

  • James Fixen - Tuesday, July 15, 2008 - link

    Had a good laugh: a smart Dutch dude became so angry that his battery of his iPhone 3G drained, that he asked some manufacturers in Linkedin to built him a rechargable, strong but small battery without funny cases or cables. The product will be out in two weeks and gives, almost 70% more energy (1770 mAh) than earlier devices, f.e. Kensington or iSound (1000 mAh). Reply
  • coco - Tuesday, July 15, 2008 - link

    Sure the battery on iPhone 3G is not that great, but what can we do? We want small size phones, powerful features and lengthy battery life.

    Just get a backup battery. I got mine from iPhoneck brands. Their new 3G backup battery is probably one of the better looking products in the market. Their website is www.iphoneck.com

  • abpages - Wednesday, May 28, 2008 - link

    Yep same here, i'm in Australia and would have bought an iPhone if it supported 3G. Such a shame. I ended up with a Samsung Blackjack and it's fantastic sofar.

    Ron Stark
  • edwinder - Sunday, July 22, 2007 - link

    Hi Anand,

    Stop defending the iPhone's lack of 3G. (You seem to keep justifying their lack of the 3G feature saying how they made a 'wise' choice). In other parts of the world, and its a very well known fact that 3G drains the battery tremendously. Yet every single phone has 3G and we work within their operating limits.

    From a technology/market demand/innovation perspective, adoption of new technologies will push the envelope that will benefit the end users (you and me). This pushes the manufacturer to keep innovating, unlike Apple, who decided to take one step back and provide less features and charge you a bomb for it, and you keep praising them.

    I'm disappointed.


  • peternelson - Tuesday, July 17, 2007 - link

    Despite the hype about the justification for using old wireless standards: ie physical space and power consumption aka battery life, I think there is another important factor they neglected to mention:

    Since 2G is less chips, less pcb assembly mounting and traces, and the chips themselves are simpler and more mature, THE OLD CHIPS MAKE IT CHEAPER TO MANUFACTURE THAN 3G.

    Simple as that. Reduced costs of production and parts make for bigger profits.

    That is the truthful reason, but they are not likely to admit that as a primary factor in the decision. It wouldn't be "cool" to tell people their equipment is outdated already.
  • Squuiid - Tuesday, July 17, 2007 - link

    I have an AT&T 8525 and disable 3G on it.

    When using MS Push I get less than 10hrs on it with 3G, I'm in NYC with full signal all day.

    On GSM it lasts all day till I get to charge it at night. So even thought I have the 3G capability, it is unusable due to ridiculous power consumption.

  • sprockkets - Saturday, July 14, 2007 - link

    Are you saying you can use edge to make voice conversations instead of GSM? I have never heard of that. So what about GPRS.

    The whole point of why you get less talk time over UMTS is because it is WCDMA and is inherit in the technology. Wikipedia it and see for yourself.

    While not real proof, if I use an edge connection for data, it sounds like a voice conversation over speakers. Sure you use edge for voice?
  • drwho9437 - Saturday, July 14, 2007 - link

    It is not clear to me from your webpage results that the faster connection wasn't largely impacted by the fact that it simply rendered more pages. That is what is the cost of rendering the page, not just getting the data.

    The talk time stuff is interesting, looks like something you could fix up in firmware easily though.
  • nvmarino - Friday, July 13, 2007 - link

    It would be helpful to know how long the battery lasted on both phones with the screen on but doing nothing.

    And what the hell did you guys talk about for 9 hours, anyway?
    "Can you hear me now?"



  • kennyb - Saturday, July 14, 2007 - link

    Excellent article. The first time i saw an iPhone i knew Apple wouldn't allow a user-replaceable battery. Why? It would ruin the iPhone's aesthetics. If you've ever bought a Mac before you'd understand. I expect Apple to incorporate a really slick mechanism to open the chassis without uglifying the iPhone sometime soon.

    Also, when i heard that 3G would not be supported, i immediately thought about [chip]space. Maybe EL Stevo mandated that the iPhone not exceed "X" mm thickness. Hey, it happened with the Powerbook G4.

    Yeah, i want one. Yeah, i don't need one.

Log in

Don't have an account? Sign up now