AudioQueueStart() method can not play music in ios4 background

In the iphone 3.x platform, I use AudioQueueStart method to play music, but 开发者_运维百科on ios4 platform, once the program into the background,then no sound, but I notice that the app is still running in background, I've added into the info.list UIBackgroundModes/Audio and applicationDidEnterBackground methods

One thing to check is that the AudioSession is active first.

In my case, I had previously set the session to inactive between song changes before starting a new song:

AudioSessionSetActive(false);

Once I removed this AudioQueueStart works just fine from the background.