Sample Code

Using AVFoundation to Play and Persist HTTP Live Streams

Play HTTP Live Streams and preserve streams on disk for offline play back.

Download

Overview

This sample provides a catalog of HTTP Live Streams (HLS) that you can play by tapping the row in the table corresponding to the stream. To manage the download of an HLS stream, tap the accessory button associated with the stream in the row in the table. Tapping the accessory button causes a transition to a new view controller which provides an interface to initiate a download, cancel an already running download, or delete a downloaded HLS stream from the device.

The sample creates and initializes an AVAggregateAssetDownloadTask for the download of an HLS stream. Only the default media selections for each of the asset’s media selection groups are downloaded (these are indicated in the HLS playlist EXT-X-MEDIA tags by a DEFAULT attribute of YES).

NOTE

  • This sample does not support saving FairPlay Streaming (FPS) content. For a version of the sample that demonstrates how to download FPS content, see FairPlay Streaming Server SDK.

Play an HTTP Live Stream

AssetListTableViewController is the main user interface of this sample. It provides a list of the assets the sample can play, download, cancel download, and delete. AssetListManager provides a list of assets to present in the AssetListTableViewController.

AssetPlaybackManager is responsible for playing downloaded assets, and it uses key-value observing (KVO) to monitor playback-related changes to the AVURLAsset, AVPlayer, and AVPlayerItem objects it manages. A player item’s status emits a KVO change notification when its status changes. The app monitors these changes and initiates playback when the status property indicates the player item is ready to play. The app observes the AVURLAsset isPlayable property to determine whether an AVPlayer can play the contents of the asset in a manner that meets user expectations. The app also observes the player currentItem property to access the player item created for a given stream.

The StreamListManager class manages loading and reading the contents of the Streams.plist file in the app bundle.

To play an item, tap one of the rows in the table. Tapping the item causes a transition to a new view controller. As part of that transition, the table view creates an AssetPlaybackManager and assigns the appropriate asset to it, as shown in the following example:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    super.prepare(for: segue, sender: sender)

    if segue.identifier == AssetListTableViewController.presentPlayerViewControllerSegueID {
        guard let cell = sender as? AssetListTableViewCell,
            let playerViewControler = segue.destination as? AVPlayerViewController else { return }

        /*
         Grab a reference for the destinationViewController to use in later delegate callbacks from
         AssetPlaybackManager.
         */
        playerViewController = playerViewControler

        // Load the new Asset to playback into AssetPlaybackManager.
        AssetPlaybackManager.sharedManager.setAssetForPlayback(cell.asset)
    }
}

Assigning an asset to the AssetPlaybackManager causes it to create an AVPlayerItem for the asset, removing any previous asset in the process:

private var asset: Asset? {
    willSet {
        /// Remove any previous KVO observer.
        guard let urlAssetObserver = urlAssetObserver else { return }
        
        urlAssetObserver.invalidate()
    }
    
    didSet {
        if let asset = asset {
            urlAssetObserver = asset.urlAsset.observe(\AVURLAsset.isPlayable, options: [.new, .initial]) { [weak self] (urlAsset, _) in
                guard let strongSelf = self, urlAsset.isPlayable == true else { return }
                
                strongSelf.playerItem = AVPlayerItem(asset: urlAsset)
                strongSelf.player.replaceCurrentItem(with: strongSelf.playerItem)
            }
        } else {
            playerItem = nil
            player.replaceCurrentItem(with: nil)
            readyForPlayback = false
        }
    }
}

The AssetPlaybackManager uses KVO to monitor the AVPlayerItem object’s status, and initiates playback when the status becomes ready to play:

playerItemObserver = playerItem?.observe(\AVPlayerItem.status, options: [.new, .initial]) { [weak self] (item, _) in
    guard let strongSelf = self else { return }
    
    if item.status == .readyToPlay {
        if !strongSelf.readyForPlayback {
            strongSelf.readyForPlayback = true
            strongSelf.delegate?.streamPlaybackManager(strongSelf, playerReadyToPlay: strongSelf.player)
        }
    } else if item.status == .failed {
        let error = item.error
        
        print("Error: \(String(describing: error?.localizedDescription))")
    }

Download an HTTP Live Stream

AssetPersistenceManager is the main class in this sample that demonstrates how to manage downloading HLS streams. It includes methods for starting and canceling downloads, deleting existing assets from the user’s device, and monitoring the download.

When the user initiates a download by tapping the accessory button in the corresponding stream’s table view cell, an instance of AssetPersistenceManager calls the following function to create an AVAggregateAssetDownloadTask object to download multiple AVMediaSelection for the AVURLAsset of the HLS stream:

func downloadStream(for asset: Asset) {

    // Get the default media selections for the asset's media selection groups.
    let preferredMediaSelection = asset.urlAsset.preferredMediaSelection

    /*
     Creates and initializes an AVAggregateAssetDownloadTask to download multiple AVMediaSelections
     on an AVURLAsset.
     
     For the initial download, we ask the URLSession for an AVAssetDownloadTask with a minimum bitrate
     corresponding with one of the lower bitrate variants in the asset.
     */
    guard let task =
        assetDownloadURLSession.aggregateAssetDownloadTask(with: asset.urlAsset,
                                                           mediaSelections: [preferredMediaSelection],
                                                           assetTitle: asset.stream.name,
                                                           assetArtworkData: nil,
                                                           options:
            [AVAssetDownloadTaskMinimumRequiredMediaBitrateKey: 265_000]) else { return }

    // To better track the AVAssetDownloadTask, set the taskDescription to something unique for the sample.
    task.taskDescription = asset.stream.name

    activeDownloadsMap[task] = asset

    task.resume()

    var userInfo = [String: Any]()
    userInfo[Asset.Keys.name] = asset.stream.name
    userInfo[Asset.Keys.downloadState] = Asset.DownloadState.downloading.rawValue
    userInfo[Asset.Keys.downloadSelectionDisplayName] = displayNamesForSelectedMediaOptions(preferredMediaSelection)

    NotificationCenter.default.post(name: .AssetDownloadStateChanged, object: nil, userInfo: userInfo)
}

NOTE

  • You cannot save a live HLS stream while it is in progress. If you try to save a live HLS stream, the system throws an exception. Only Video On Demand (VOD) streams support offline playback.

Cancel an HTTP Live Stream

Tap the accessory button in the corresponding stream’s table view cell to reveal the accessory view, then tap Cancel to stop downloading the stream. The following function in AssetPersistenceManager cancels the download by calling the URLSessionTask cancel() method.

func cancelDownload(for asset: Asset) {
    var task: AVAggregateAssetDownloadTask?

    for (taskKey, assetVal) in activeDownloadsMap where asset == assetVal {
        task = taskKey
        break
    }

    task?.cancel()
}

Remove an HTTP Live Stream from Disk

Tap the accessory button in the corresponding stream’s table view cell to reveal the accessory view, then tap Delete to delete the downloaded stream file. The following function in AssetPersistenceManager removes a downloaded stream on the device. First the asset URL corresponding to the file on the device is identified, then the FileManager removeItem(at:) method is called to remove the downloaded stream at the specified URL.

func deleteAsset(_ asset: Asset) {
    let userDefaults = UserDefaults.standard

    do {
        if let localFileLocation = localAssetForStream(withName: asset.stream.name)?.urlAsset.url {
            try FileManager.default.removeItem(at: localFileLocation)

            userDefaults.removeObject(forKey: asset.stream.name)

            var userInfo = [String: Any]()
            userInfo[Asset.Keys.name] = asset.stream.name
            userInfo[Asset.Keys.downloadState] = Asset.DownloadState.notDownloaded.rawValue

            NotificationCenter.default.post(name: .AssetDownloadStateChanged, object: nil,
                                            userInfo: userInfo)
        }
    } catch {
        print("An error occured deleting the file: \(error)")
    }
}

Measure Playback Performance

PerfMeasurements contains utility code to measure key performance indicators (KPI) during streaming playback. This code makes use of the AVPlayerItemAccessLog for many of its calculations. An AVPlayerItemAccessLog object accumulates key metrics about network playback and presents them as a collection of AVPlayerItemAccessLogEvent instances. Each event instance collates the data that relates to each uninterrupted period of playback.

NOTE

  • You can view the various performance indicators in the console during playback.

For example, here’s the code to calculate the total time spent playing the stream, obtained from the AVPlayerItemAccessLog:

var totalDurationWatched: Double {
    // Compute total duration watched by iterating through the AccessLog events.
    var totalDurationWatched = 0.0
    if accessLog != nil && !accessLog!.events.isEmpty {
        for event in accessLog!.events where event.durationWatched > 0 {
                totalDurationWatched += event.durationWatched
        }
    }
    return totalDurationWatched
}

See Also

HTTP Live Streaming

About the Common Media Application Format with HTTP Live Streaming

Understand the Common Media Application Format as it applies to HTTP Live Streaming