AVPlayer not synchronized

Question

I'm really out of ideas so I'll have to ask you guys again...

I'm building an iPhone application which uses three instances of AVPlayer. They all play at the same time and it's very important that they do so. I used to run this code:

CMClockRef syncTime = CMClockGetHostTimeClock();
CMTime hostTime = CMClockGetTime(hostTime);
[self.playerOne setRate:1.0f time:kCMTimeInvalid atHostTime:hostTime];
[self.playerTwo setRate:1.0f time:kCMTimeInvalid atHostTime:hostTime];
[self.playerThree setRate:1.0f time:kCMTimeInvalid atHostTime:hostTime];

which worked perfectly. But a few days ago it just stopped working, the three players are delayed by about 300-400ms (which is way to much, everything under 100ms would be okay). Two of these AVPlayer have some Audio processing, which takes some time more than the "normal" AVPlayer, but it used to work before and the currentTime property tells me, that these players are delayed, so the syncing seems to fail.

I have no idea why it stopped working, I didn't really changed something, but I'm using an observer where i can ask the self.playerX.currentTime property, which gives me a delay of about .3-.4 seconds... I already tried to resync the players if delay>.1f but the delay is still there. So I think the audio processing of player1 and 2 can't be responsable for the delay, as the currentTime property does know they are delayed (i hope you know what I mean). Maybe someone of you guys know why I'm having such a horrible delay, or is able to provide me another idea.

Thanks in advance!

Answer 1

So, I found the solution. I forgot to [self.playerX prerollAtRate:]. I thought if the observer is AVPlayerReadyToPlay it means, that the player is "really" ready. In fact, it does not. After AVPlayer is readyToPlay, it has to be pre rolled. Once that is done you can sync your placer. The delay is now somewhere at 0.000006 seconds.

Answer 2

Full func to sync avplayer's across multiple iOS devices

private func startTribePlayer() {
    let dateFormatterGet = DateFormatter()
    dateFormatterGet.dateFormat = "yyyy-MM-dd"
    guard let refDate = dateFormatterGet.date(from: "2019-01-01") else { return }
    let tsRef = Date().timeIntervalSince(refDate)
    //currentDuration is avplayeritem.duration().seconds
    let remainder = tsRef.truncatingRemainder(dividingBy: currentDuration)
    let ratio = remainder / currentDuration
    let seekTime = ratio * currentDuration
    let bufferTime = 0.5
    let bufferSeekTime = seekTime + bufferTime
    let mulFactor = 10000.0
    let timeScale = CMTimeScale(mulFactor)
    let seekCMTime = CMTime(value: CMTimeValue(CGFloat(bufferSeekTime * mulFactor)), timescale: timeScale)
    let syncTime = CMClockGetHostTimeClock()
    let hostTime = CMClockGetTime(syncTime)
    tribeMusicPlayer?.seek(to: seekCMTime, toleranceBefore: .zero, toleranceAfter: .zero, completionHandler: { [weak self] (successSeek) in
        guard let tvc = self, tvc.tribeMusicPlayer?.currentItem?.status == .readyToPlay else { return }
        tvc.tribeMusicPlayer?.preroll(atRate: 1.0, completionHandler: { [tvc] (successPreroll) in
            tvc.tribePlayerDidPlay = true
            tvc.tribeMusicPlayer?.setRate(1.0, time: seekCMTime, atHostTime: hostTime)
        })
    })
}