Though the RC has been out for some time, and other builds before it, most of the multitasking features have gone relatively untested as they require applications to explicitly use APIs for background functionality. We were excited to play around with background audio today when Pandora released its iOS 4.0 tested, background-audio packing update. As far as we're aware, Pandora Radio is the first and only application in the app store right now supporting background audio playback.

The natural first test was to determine what impact background audio playback has on the battery life of our iPhone 3GSes. To do so, we loaded up our test page which cycles through a loop of article pages and galleries - simulating typical web browsing use - and left pandora playing in the background. Anand was testing over 3G, while I tested WiFi.

After about an hour of testing, I noticed that audio had begun skipping on my iPhone. To be completely honest, at first I thought this was part of the song I was listening to. Then I suspected some sort of buffering issue, but audio stuttering continued to get worse. Finally I decided to interrupt the test and try switching applications, when I noticed the phone had become unresponsive, rejecting all input. Mashing buttons did nothing, including the lock button. It looks like the following, and sounds like a techno song:

While I was sending the video to Anand, his iPhone 3GS running the exact same test but over 3G developed the same audio loop issue, forcing him to reboot. My iPhone eventually fixed itself after about 5 minutes of skipping, resuming audio playback and becoming responsive again. It's still playing right now, but Safari has begun crashing periodically while Pandora is playing in the background. Luckily, the audio has not started skipping again.
It’s difficult to tell at this point whether the issue lies with Pandora or iOS 4.0. Considering normal iPod playback works in the background just fine and possibly uses the same API, it’s entirely possible this a Pandora problem - especially considering it released just today, and this is a new feature. The other possibility is that the combination of our Safari page load test and Pandora in the background is using too much RAM, though iOS 4.0 is supposed to close background applications as the device gets low on RAM.
It also plausible that there's a problem with the scheduler in iOS 4.0. The combination of CPU load from our script, audio playback, and the fact that my iPhone eventually resumed being responsive leads us in that direction.
Either way, background Pandora streaming has become something of a poster child for demonstrating to end users that multitasking works - its execution needs to be flawless before the launch of iPhone 4.


View All Comments

  • sxpert - Tuesday, June 22, 2010 - link

    sounds awfully like a slow winding memory leak somewhere...
    after a while, the entire RAM of the device is consumed by the leaking application, and kaboom goes the device
  • kring - Tuesday, June 22, 2010 - link

    I think it's an audio issue in general, I was playing angry birds for about an hour and I notice the audio breaking up and a bit of a delay scrolling back and forth across the screen. I bet there's some sort of issue with the way it handles all audio now.

    I wasn't multi tasking either. on 3GS
  • blwest1978 - Tuesday, June 22, 2010 - link

    I listened to pandora last night for over an hour in the background while using safari and other apps and never once got a skip.

    I have a feeling we've just reported one incident, not a trend.
  • groove11joel - Wednesday, June 23, 2010 - link

    FWIW, I'm getting tons of skipping while listening to Pandora. I never experienced it before upgrading. I'm on a 3G phone. It's seemed generally more sluggish since the upgrade as well. Reply
  • Kensei - Tuesday, June 22, 2010 - link

    I live in Japan and just received a Pandora update this morning (June 23). I suppose a follow up should be done to see if this fixed the problem. Reply
  • CZroe - Wednesday, June 23, 2010 - link

    Where were you when I seemed the be the only human alive complaining about A2DP ant playing well with WiFi on the same 3G iPhone? It was vastly improved with the 3GS but after the buffer cleared it was impossible to use, say, Pandora over WiFi and listen over A2DP. Reply
  • Drizzt321 - Wednesday, June 23, 2010 - link

    I don't think Pandora is the only background audio app. I think the KCRW streaming player does so as well. At least, that's what I keep hearing when they advertise it on the radio.

    KCRW is a NPR station in Santa Monica, CA that has a very eclectic mix of independent musicians and programming.
  • jur9103 - Thursday, June 24, 2010 - link

    That happen also to me when playing youtube video. I had to hard restart the phone iPhone 3GS. Hope for fix soon. Reply
  • jamesx4 - Friday, July 30, 2010 - link

    After my iOS4 upgrade I started seeing the exact same thing on my 3G. Pandora runs fine for a while then begins to skip or stutter. Eventually, phone becomes unresponsive. A reset brings me back to iPhone goodness until I run Pandora again for a while. Also, notice stuttering with a couple of games that I didn't see before upgrade, namely Angry Birds and Fruit Ninja. Not sure if I can tie the stutter in the games to sound yet. Reply
  • kcvmsu - Saturday, July 31, 2010 - link

    I have both Pandora and Slacker. I have the problem you mention with Pandora skipping. It happens to me after listening for several minutes. I also have Slacker and it doesn't skip but will stop playing a song and skip to the next song. Both apps will "hang" eventually. I have another app where I listen to the sports radio show of Dan Patrick. It doesn't have the problem however I don't listen as long to it as I do the music apps. Reply

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