iOS: How to Have a Certain Action Occur for a Specific Time Duration?

In my app I'm using AVAudioPlayer objects to hold the mp3 files. I have several occasions where I wish to lower the sound level of the files while they are being played.

I understand some of what I'm supposed to be doing, but I don't understand how I define the duration and how do I command that something will happen only for that duration.

I'm looking for something like this:

AVAudioPlayer * aud1 = [I have a method to get the file];
AVAudioPlayer * aud2 = [I have a method to get the file];
NSTimeInterval * aud1_ti = aud1.duration //I haven't tried this yet 开发者_StackOverflow社区- is this the right way to get the mp3 play duration?
[aud1 play];
[aud2 play];
while (aud1_ti)
     aud2.volume = 0.5;
aud2.volume = 1.0

To say it in words - I wish that while aud1 is playing, aud2 volume will be reduced in half; and once the file had reached its end the aud2 volume will get back to its full level. I couldn't understand from the documentation how to do that.

Can anyone assist?

---

Rather than basing this off of the duration what you probably want to do is have the delegate of your AVAudioPlayer respond to – audioPlayerDidFinishPlaying:successfully: and reset the volume at that time. On a very, very basic level you will have something like this:

- (void)startPlaying {
     self.aud1.delegate = self;
     [self.aud1 play];

     self.aud2.volume = 0.5;
     [self.aud2 play];
}

- (void)audioPlayerDidFinishPlaying:(AVAudioPlayer *)player successfully:(BOOL) {
     if (self.aud2) {
          self.aud2.volume = 1.0;
     }
}

Note, the code above is obviously incomplete but should point you in the right direction.