Cache HLS video while playing with AVAssetDownloadTask

问题

I am trying cache an HLS stream while I am playing it. I was following the Apple documentation on this (the section Playing Offline Assets):

https://developer.apple.com/library/archive/documentation/AudioVideo/Conceptual/MediaPlaybackGuide/Contents/Resources/en.lproj/HTTPLiveStreaming/HTTPLiveStreaming.html#//apple_ref/doc/uid/TP40016757-CH11-SW1

I've implemented the following method - which should make my HLS streams download while playing:

func downloadAndPlayAsset(_ asset: AVURLAsset) {
    // Create new AVAssetDownloadTask for the desired asset
    // Passing a nil options value indicates the highest available bitrate should be downloaded
    let downloadTask = downloadSession.makeAssetDownloadTask(asset: asset,
                                                             assetTitle: assetTitle,
                                                             assetArtworkData: nil,
                                                             options: nil)!
    // Start task
    downloadTask.resume()

    // Create standard playback items and begin playback
    let playerItem = AVPlayerItem(asset: downloadTask.urlAsset)
    player = AVPlayer(playerItem: playerItem)
    player.play()
}

The problem is it just doesn't download the video, only plays the stream. I've also implemented the delegates, but then none of them get called:

func urlSession(_ session: URLSession, assetDownloadTask: AVAssetDownloadTask, didLoad timeRange: CMTimeRange, totalTimeRangesLoaded loadedTimeRanges: [NSValue], timeRangeExpectedToLoad: CMTimeRange)

func urlSession(_ session: URLSession, assetDownloadTask: AVAssetDownloadTask, didFinishDownloadingTo location: URL)

func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?)

Rather strangely, I noticed that the next time I open the app, the assetDownloadURLSession.getAllTasks returns pending tasks for my downloads from the last session. So it doesn't download the streams but it does add them to a pending queue. Do you know what would be the rationale behind that? I had a theory that the stream being downloaded and the live stream use different quality so it does need to be redownloaded in the right quality. So I created an HLS stream for testing with just one quality but the result is still the same.

If I remove the lines assigning the AVPlayerItem to AVPlayer the download starts and all the delegates gets called. So the download on its own work, but anytime I try to play it just stops.

Thanks for help!

Tomas

回答1:

Did that happened on iOS13 or newer? https://forums.developer.apple.com/thread/121097 If so, we met the same problem maybe, and Apple just hasn't given us any hits

来源：https://stackoverflow.com/questions/58206226/cache-hls-video-while-playing-with-avassetdownloadtask