iPhone - why does AVAudioPlayer currentTime return a negative value?

Question

Hi

When does the AVAudioPlayer's currentTime method return a negative value? The audio file is playing (I am putting in a check before getting currentTime) but making a call to currentTime returns a negative value.

Any ideas? Thanks

if(thePlayer != nil && [thePlayer isPlaying]){
    double playerTime = [thePlayer currentTime];
    NSLog(@"Player Time: %f", playerTime);
}

Output

Player Time: -0.019683

Answer 1

Are you testing this on the simulator? There are several bugs with AVAudioPlayer on the simulator. One is that the currentTime can be a very large positive or negative number. Even if you set the currentTime to a particular number, it will still often show something different. As far as I know this is only an issue on the simulator and not when running on a device.

Here is the code I use to set the currentTime property of an AVAudioPlayer instance:

- (void)safeSetCurentTime:(NSTimeInterval)newTime {
self._player.currentTime = newTime;
if (self._player.currentTime != newTime)
{
    // code falls through to here all the time
            // the second attempt _usually_ works.
    [self prepareAudioForPlayback];
    self._player.currentTime = newTime;
    //NSLog(@"Set time failed");
}

}

Answer 2

Are you still having this problem? I'm seeing the same thing. On the device, even when I specifically set the currentTime to 0. I can log the currentTime and it is zero. But when I play, it still jumps back about .04 seconds and then starts.

Did you find a solution?

Answer 3

I believe this issue is fixed the iOS4 beta 2 SDK release, so you shouldn't see it on the iPhone. See here. However, I think we're stuck with the problem on the iPad until iOS4 is available on that device.

Anyone know of a workaround? Any way to predict how the current time will be incorrectly reported, so a correction factor can be applied? What I'm seeing is that the current time is reported to be a few seconds behind the actual playback time (which could be negative, if you're near the start of he audio), and it tracks along with the correct position. So perhaps there's some offset that can be applied whenever the app is used on an earlier iOS version?

Answer 4

I found a workaround that fixes the problem on the iPad, which is workable until iOS4 is released for the iPad and fixes the issue.

Keep hold of the audio buffer, and when you're about to resume playback after pausing/stopping, reload the audio buffer into the AVAudioPlayer instance, set currentTime to where you want playback to resume from, and then resume playback.

Works perfectly for me, and reloading the audio buffer seems very fast.