AVAudioEngine incorrect time management and callback for AVAudioPlayerNode - ios8

Question

I have a serious issue with the new audio engine in iOS8. I have an application, which is built with AVAudioPlayer and I am trying to figure out a way to migrate to the new architecture, however I bumped into the following problem (which I'm sure you would agree, is a serious and basic obstacle):
My header file:
AVAudioEngine *engine;
AVAudioMixerNode *mainMixer;
AVAudioPlayerNode *player;
My m file (inside the viewDidLoad):
engine = [[AVAudioEngine alloc] init];
player = [[AVAudioPlayerNode alloc] init];
[engine attachNode:player];
NSURL *fileUrl = [[NSURL alloc] initFileURLWithPath:[[NSBundle mainBundle] pathForResource:#"test" ofType:#"mp3"]];
AVAudioFile *file = [[AVAudioFile alloc] initForReading:fileUrl error:nil];
NSLog(#"duration: %.2f", file.length / file.fileFormat.sampleRate);
[player scheduleFile:file atTime:nil completionHandler:^{
AVAudioTime *nodeTime = player.lastRenderTime;
AVAudioTime *playerTime = [player playerTimeForNodeTime:nodeTime];
float secs = (float)playerTime.sampleTime / file.fileFormat.sampleRate;
NSLog(#"finished at: %.2f", secs);
}];
mainMixer = [engine mainMixerNode];
[engine connect:player to:mainMixer format:file.processingFormat];
[engine startAndReturnError:nil];
[player play];
The above code initializes the engine and a node, then starts playing back whatever file I'm using. First it prints out the duration of the music file, then, after finishing playback, in the callback function, it prints the current time of the player. These two should be the same or in a worst case scenario, very, very close to each other, but this is not the case, the difference between these two values is very big, e.g.
duration: 148.51
finished at: 147.61
Am I doing something wrong? This should be fairly straight forward, I've tried with different file formats, file lengths, tens of music files, but the difference is always around or just under 1 second.

Answer 1

Update:
As of iOS 11 you can specify the completionCallbackType: AVAudioPlayerNodeCompletionCallbackType
dataConsumed:
A completion handler indicating that the buffer or file data has been consumed by the player.
dataRendered:
The buffer or file data that has been rendered by the player.
dataPlayedBack:
A completion handler indicating that the buffer or file has finished playing.
More info: Documentation
Original:
According to Apple's documentation for scheduleFile:atTime:completionHandler:
It is possible for the completionHandler to be called before rendering
begins or before the file is played completely.