AVPlayer seeking and periodicTimeObservers

Hi all,

We are using AVPlayer to play our audio only HLS streams and are seeing what looks like a threading issue with the currentTime() method on AVPlayer vs the times reported by using the periodicTimeObserver.

Here's the scenario:

1. A class registers as a periodicTimeObserver using 0.1 seconds as the desired time interval.

2. Lets say the current time (as reported to the periodic observer) reaches 8.8 seconds.

3. On a separate thread, we have the player seek to the currentTime() + 2 seconds.

4. Within the completion block of the call to seek, we read & report what the new currentTime() is

5. While this is happening, you still listen to the periodicTimeObserver callbacks.

6. You'll notice the time reported by the call to currentTime() within the seek completion block is actually AFTER the currentTime() as reported by the periodicTimeObserver.

Here it is in code:

let underlyingPlayer: AVQueuePlayer = ...
underlyingPlayer.seek(to: newPosition, toleranceBefore: kCMTimeZero, toleranceAfter: kCMTimeZero, completionHandler: { [weak self] success in
     let time = underlyingPlayer.currentTime
     print("After seeking, the current time is \(time)")

     completionHandler?(error, time)
})

// periodic time observer is set up as the following with an interval of 0.1 seconds
let underlyingTimeObservingQueue = DispatchQueue(label: "com.company.player.timeObserver.queue", qos: DispatchQoS.userInitiated)

let valueInterval = CMTimeMakeWithSeconds(interval, 1000)
    return underlyingPlayer.addPeriodicTimeObserver(forInterval: valueInterval, queue: underlyingTimeObservingQueue) { time in
      print("periodic time is \(CMTimeGetSeconds(time))")
      return block(CMTimeGetSeconds(time))
    }
}

When you run this, here's the output we receive:

periodicTime is 7.701181537

periodicTime is 7.801130009

periodicTime is 7.900316636

periodicTime is 8.000758814

periodicTime is 8.100601498

periodicTime is 8.201145766

periodicTime is 8.301150409

periodicTime is 8.401138697

periodicTime is 8.501144148

periodicTime is 8.601161655

periodicTime is 8.701154072

periodicTime is 8.800160082

After seeking, the current time is 10.88 <----------------- This is the result returned by the seek call's completion block

periodicTime is 10.736309528

periodicTime is 10.736393196

periodicTime is 10.801075743

periodicTime is 10.900429325

periodicTime is 11.000907073

periodicTime is 11.100982256

periodicTime is 11.201173809

periodicTime is 11.300147113

periodicTime is 11.401182831

periodicTime is 11.500769324

periodicTime is 11.600593684

periodicTime is 11.701193966

periodicTime is 11.800258566

periodicTime is 11.900176181

periodicTime is 12.000423167

This seems like a bug within AVPlayer, but wanted to check here before filing it.

We couldn't really find any workarounds for this, but here's what we tried so far:

1. Unregistering all periodicTimeObservers right before seeking, and adding them back in the seek completion handler

2. Dispatch_sync the call to currentTime() within the seek method's completion block

However, none of these solutions fixed the problem.

Does anyone have any ideas about what's going on?