从 AVPlayer 播放器定期时间观察器块更新 MPNowPlayingInfoCenter 中的播放时间的问题

Question

I have an issue with updating playing info. Please have a look at the attached gif. In the end of the record playback sets to incorrect value.

I update the value by the key MPNowPlayingInfoPropertyElapsedPlaybackTime from the timer block. I check if the value is valid, convert it to seconds and set the value. Value for MPMediaItemPropertyPlaybackDuration is set from the initializer.

The closest solution I could find is to set the playback time again in playerDidFinishedPlaying func. In this case the progress slider goes to the end but I still can see that it jumps back for a moment.

Here is an implementation of player:

import AVFoundation
import MediaPlayer

class Player {
    var onPlay: (() -> Void)?
    var onPause: (() -> Void)?
    var onStop: (() -> Void)?
    var onProgressUpdate: ((Float) -> Void)?
    var onTimeUpdate: ((TimeInterval) -> Void)?
    var onStartLoading: (() -> Void)?
    var onFinishLoading: (() -> Void)?

    private var player: AVPlayer?
    private var timeObserverToken: Any?
    private var durationSeconds: Float64 = 0

    private static let preferredTimescale = CMTimeScale(NSEC_PER_SEC)
    private static let seekTolerance = CMTimeMakeWithSeconds(1, preferredTimescale: preferredTimescale)

    private var nowPlayingInfo = [String : Any]() {
        didSet {
            MPNowPlayingInfoCenter.default().nowPlayingInfo = nowPlayingInfo
        }
    }

    init(url: URL, name: String) {
        self.nowPlayingInfo[MPMediaItemPropertyTitle] = name

        let asset = AVURLAsset(url: url)

        onStartLoading?()

        asset.loadValuesAsynchronously(forKeys: ["playable"]) { [weak self] in
            guard let self = self else { return }

            let durationSeconds = CMTimeGetSeconds(asset.duration)

            self.durationSeconds = durationSeconds
            self.nowPlayingInfo[MPMediaItemPropertyPlaybackDuration] = Int(durationSeconds)

            let playerItem = AVPlayerItem(asset: asset)

            let player = AVPlayer(playerItem: playerItem)
            player.actionAtItemEnd = .pause

            self.player = player

            self.configureStopObserver()
            self.setupRemoteTransportControls()

            self.onTimeUpdate?(0)
            self.onFinishLoading?()
        }
    }

    func seek(progress: Float) {
        guard let player = player else { return }

        let targetTimeValue = durationSeconds * Float64(progress)
        let targetTime = CMTimeMakeWithSeconds(targetTimeValue, preferredTimescale: Self.preferredTimescale)

        let tolerance = CMTimeMakeWithSeconds(1, preferredTimescale: Self.preferredTimescale)

        player.seek(to: targetTime, toleranceBefore: tolerance, toleranceAfter: tolerance)
    }

    func playPause() {
        guard let player = player else { return }

        if player.isPlaying {
            player.pause()

            onPause?()
        } else {
            let currentSeconds = CMTimeGetSeconds(player.currentTime())

            if durationSeconds - currentSeconds < 1 {
                let targetTime = CMTimeMakeWithSeconds(0, preferredTimescale: Self.preferredTimescale)

                player.seek(to: targetTime)
            }

            player.play()

            onPlay?()
        }
    }

    private func configureStopObserver() {
        guard let player = player else { return }

        NotificationCenter.default.addObserver(self,
                                               selector: #selector(playerDidFinishedPlaying),
                                               name: .AVPlayerItemDidPlayToEndTime,
                                               object: player.currentItem)

    }

    @objc private func playerDidFinishedPlaying() {
        guard let player = player else { return }

        let currentSeconds = CMTimeGetSeconds(player.currentTime())

        self.onTimeUpdate?(TimeInterval(currentSeconds))

        // self.nowPlayingInfo[MPNowPlayingInfoPropertyElapsedPlaybackTime] = Int(currentSeconds)
        // self.nowPlayingInfo[MPNowPlayingInfoPropertyPlaybackRate] = player.rate

        onStop?()
    }

    func handleAppearing() {
        subscribeToTimeObserver()
        configureAndActivateAudioSession()
    }

    func handleDisappearing() {
        unsubscribeFromTimeObserver()
        deactivateAudioSession()
    }

    private func configureAndActivateAudioSession() {
        let audioSession = AVAudioSession.sharedInstance()

        try? audioSession.setCategory(.playback, mode: .default, options: [])
        try? audioSession.setActive(true, options: [])
    }

    private func deactivateAudioSession() {
        guard let player = player else { return }

        player.pause()

        try? AVAudioSession.sharedInstance().setActive(false, options: [])
    }

    private func subscribeToTimeObserver() {
        guard let player = player else { return }

        let preferredTimescale = CMTimeScale(NSEC_PER_SEC)

        let interval = CMTimeMakeWithSeconds(0.1, preferredTimescale: preferredTimescale)

        timeObserverToken = player.addPeriodicTimeObserver(forInterval: interval, queue: nil, using: { [weak self] time in
            guard let self = self else { return }

            let timeIsValid = time.flags.rawValue & CMTimeFlags.valid.rawValue == 1
            let timeHasBeenRounded = time.flags.rawValue & CMTimeFlags.hasBeenRounded.rawValue == 1

            if !timeIsValid && !timeHasBeenRounded {
                return
            }

            let currentSeconds = CMTimeGetSeconds(time)

            self.onTimeUpdate?(TimeInterval(currentSeconds))

            self.nowPlayingInfo[MPNowPlayingInfoPropertyElapsedPlaybackTime] = Int(currentSeconds)
            self.nowPlayingInfo[MPNowPlayingInfoPropertyPlaybackRate] = player.rate

            let progress = Float(currentSeconds / self.durationSeconds)

            self.onProgressUpdate?(progress)
        })
    }

    private func unsubscribeFromTimeObserver() {
        if let token = timeObserverToken, let player = player {
            player.removeTimeObserver(token)
        }
    }

    private func setupRemoteTransportControls() {
        let commandCenter = MPRemoteCommandCenter.shared()

        commandCenter.changePlaybackPositionCommand.addTarget { [weak self] event in
            guard
                let self = self,
                let player = self.player

                else { return .commandFailed }

            if let event = event as? MPChangePlaybackPositionCommandEvent {
                let targetTime = CMTimeMakeWithSeconds(event.positionTime, preferredTimescale: Self.preferredTimescale)

                player.seek(to: targetTime, toleranceBefore: Self.seekTolerance, toleranceAfter: Self.seekTolerance)

                return .success
            }

            return .commandFailed
        }

        commandCenter.playCommand.addTarget { [weak self] event in
            guard
                let self = self,
                let player = self.player

                else { return .commandFailed }

            if !player.isPlaying {
                player.play()
                self.onPlay?()

                return .success
            }

            return .commandFailed
        }

        commandCenter.pauseCommand.addTarget { [weak self] event in
            guard
                let self = self,
                let player = self.player

                else { return .commandFailed }

            if player.isPlaying {
                player.pause()
                self.onPause?()

                return .success
            }

            return .commandFailed
        }
    }
}

private extension AVPlayer {
    var isPlaying: Bool {
        return rate != 0 && error == nil
    }
}

Answer 1

You don't need to set the elapsed time over and over again.
Just update elapsedTime when you start playing a new asset or after seeking.
If you set playbackRate properly (default should be 1.0), nowPlayingInfoCenter updates the time itself.

Answer 2

I have exactly the same problem. To mitigate it I update the now playing info (playback rate/duration/position) when the player's timeControlStatus property becomes paused . Something like this:

    observations.append(player.observe(\.timeControlStatus, options: [.old, .new]) { [weak self] (player, change) in

        switch player.timeControlStatus {
        case .paused:
            self?.updateNowPlayingInfo()
        case .playing:
            self?.updateNowPlayingInfo()
        case .waitingToPlayAtSpecifiedRate:
            break
        default:
            DDLogWarn("Player: unknown timeControlStatus value")
        }

    })

This way I don't have the unpleasant jump back you're talking about.

Answer 3

I had the same problem...

For me, I'd update the playback time in the background when the player's currentTime variable was set to a different time.

Since it was my app updating the value without input from the user, it just never worked. I was pretty convinced I'd never get it working.

FINALLY - something that worked for me. First a couple rules.

1. Always keep your own copy of the whole info dictionary and update that.
2. Set the whole info dictionary at the same time (IE don't set individual keys on the MPNowPlayingInfoCenter.default().nowPlayingInfo directly. It doesn't work as well as you'd like.) Update the whole thing.
3. DO NOT update the dictionary multiple times in succession or rapid-succession. So if you have methods to update the rate and playback time that frequently get called together, be very sure that you're only updating both keys in your local dictionary and setting the nowPlayingInfo once.

Eg - here is some code from me to ya'll for pondering.

class InfoCenter {

private static var info = [String : Any]()

class func initNowPlayingInfo(_ param: Any) {
    // setup your info dictionary here
    DispatchQueue.main.async(execute: {
        MPNowPlayingInfoCenter.default().nowPlayingInfo = info
    })
}

class func syncPlaybackRate(setInfo set: Bool) {
    DispatchQueue.main.async(execute: {
        if UIApplication.shared.applicationState != .inactive {
            if let player = player {
                info[MPNowPlayingInfoPropertyElapsedPlaybackTime] = player.currentPlaybackRate
                if set {
                    MPNowPlayingInfoCenter.default().nowPlayingInfo = info
                }
            }
        }
    })
}

class func syncPlaybackTime(setInfo set: Bool) {
    if UIApplication.shared.applicationState != .inactive {
        if let player = player {
            DispatchQueue.main.async(execute: {
                if let song = song {
                    info[MPNowPlayingInfoPropertyPlaybackProgress] = player.currentPlaybackTime / song.getEndTime()
                }
                info[MPNowPlayingInfoPropertyElapsedPlaybackTime] = player.currentPlaybackTime
                if set {
                    MPNowPlayingInfoCenter.default().nowPlayingInfo = info
                }
            })
        }
    }
}

}