AVAssetDownloadTask iOS13

Question

Tried iOS13.0 and iOS13.1 and still not working, I tried both AVAggregateAssetDownloadTask and AVAssetDownloadURLSession but none of them working. Not any delegate was called to tell me error of finish, and I found downloaded cache was only 25Kb what was not the right size.

The error is:

Error Domain=AVFoundationErrorDomain Code=-11800 "The operation could not be completed" UserInfo={NSLocalizedDescription=The operation could not be completed, _NSURLErrorFailingURLSessionTaskErrorKey=BackgroundAVAssetDownloadTask <AFDCA3CC-FA49-488B-AB16-C74425345EE4>.<1>, _NSURLErrorRelatedURLSessionTaskErrorKey=(

    "BackgroundAVAssetDownloadTask <AFDCA3CC-FA49-488B-AB16-C74425345EE4>.<1>"

), NSLocalizedFailureReason=An unknown error occurred (-16654)}

Answer 1

Found out AVAssetDownloadURLSession can only download HLS with master playlist structure which contains codec attribute into EXT-X-STREAM-INF m3u8 meta on iOS 13+.

I have no idea if this is a bug or function restriction. (m3u8 meta have no CODECS attribute can be played with AVFoundation, but can't be downloaded with AVAssetDownloadURLSession)

Anyway, the solution is:

If you have HLS master playlist:

add CODECS attribute into your #EXT-X-STREAM-INF in m3u8 meta. e.g.

#EXTM3U
#EXT-X-VERSION:3
#EXT-X-STREAM-INF:BANDWIDTH=63701,CODECS="mp4a.40.34"
playlist.m3u8

If you haven't HLS master playlist yet:

You have to make a master playlist even if you're not supporting adaptive streaming.
The master playlist is the only m3u8 which can contain #EXT-X-STREAM-INF hence CODECS attribute.

Answer 2

So, I found out that the 'AVAssetDownloadTask' had some error in calling delegates in iOS 13 (13.1,13.2.13.3). Finally, in iOS 13.4.1, Apple has fixed this error and now delegates have called after setting delegate and starting the task. Below is what I used to start downloading the m3u8 file from the server and saving it as an Asset to play later offline.

func downloadVideo(_ url: URL) {
    let configuration = URLSessionConfiguration.background(withIdentifier: currentFileName)

    let downloadSession = AVAssetDownloadURLSession(configuration: configuration,
                                                    assetDownloadDelegate: self,
                              delegateQueue: OperationQueue.main)
    // HLS Asset URL
    let asset = AVURLAsset(url: url)

    // Create new AVAssetDownloadTask for the desired asset
    let downloadTask = downloadSession.makeAssetDownloadTask(asset: asset,
                                                             assetTitle: currentFileName,
                                                             assetArtworkData: nil,
                                                             options: nil)
    // Start task and begin download
    downloadTask?.resume()
}

I tried this on iOS 12 and iOS 13.4.1 and it is working as expected. Also, it was already on the Apple Developer Forums here. Hope this helps someone.