Video Streaming Fails when using AVAssetResourceLoader - ios

Question

We are using video streaming in our Swift IOS application and it works very well. The problem is that we would like to use AVAssetResourceLoader so we can make the requests to the streaming server using our own URLSession rather than whatever AVPlayer uses (I have been completely unable to find out what session AVPlayer uses or how to influence what session it uses.)
The exact behavior is that shouldWaitForLoadingOfRequestedResource is called once for two bytes on on the .m3u8 file then it is called again asking for the whole file, and then (based on the start time) the correct .ts file is requested. After we fetch the .ts file the video player simply doesn't do anything further.
This happens whether or not we use a sample streaming video file "https://tungsten.aaplimg.com/VOD/bipbop_adv_example_v2/master.m3u8" or our own server. The sequence is identical if we don't use AVAssetResourceLoader (we can tell from our server.) right up until the .ts file is requested. At that point when we don't use the custom loader the AvPlayer brings up the video and keeps requesting .ts files. If we comment out all other interactions with the AVPlayer including setting the initial time the behavior is identical so I am only going to include the code from viewDidLoad and shouldWaitForLoadingOfRequestedResource.
Again if we simply remove the "xyzzy" prefix so that AVAssetResourceLoader isn't used, everything works. Also, I guess importantly, if we target a video file that is not a streaming file everything works either way.
One more thing our transformation of the mime type for the .ts file produced some kind of weird dynamic uti, but this doesn't seem to have anything to do with the problem because even if we hardcode the uti the same thing happens.
override func viewDidLoad() {
super.viewDidLoad()
avPlayer = AVPlayer()
avPlayerLayer = AVPlayerLayer(player: avPlayer)
videoView.layer.insertSublayer(avPlayerLayer, at: 0)
videoView.backgroundColor = UIColor.black
url = URL(string: "xyzzy" + currentPatient.videoURL())!
let asset = AVURLAsset(url: url)
asset.resourceLoader.setDelegate(self, queue: DispatchQueue.main)
let item = AVPlayerItem(asset: asset)
let avPlayerItem = item
avPlayer.replaceCurrentItem(with: avPlayerItem)
videoScrollView.delegate = self
videoScrollView.minimumZoomScale = 1.0
videoScrollView.maximumZoomScale = 6.0
}
func resourceLoader(_ resourceLoader: AVAssetResourceLoader, shouldWaitForLoadingOfRequestedResource loadingRequest: AVAssetResourceLoadingRequest) -> Bool {
let urlString = loadingRequest.request.url?.absoluteString
let urlComponents = urlString?.components(separatedBy: "xyzzy")
let url = URL(string: urlComponents![1])
let request = loadingRequest.dataRequest!
let infoRequest = loadingRequest.contentInformationRequest
let task = globalSession.dataTask(with: url!) { (data, response, error) in
self.avPlayerThread.async {
if error == nil && data != nil {
let uti = UTTypeCreatePreferredIdentifierForTag(kUTTagClassMIMEType, response?.mimeType as! CFString, nil)
if let infoRequest = infoRequest {
infoRequest.contentType = uti?.takeRetainedValue() as? String
if request.requestsAllDataToEndOfResource == false {
infoRequest.contentLength = Int64(request.requestedLength)
} else {
infoRequest.contentLength = Int64((data?.count)!)
}
infoRequest.isByteRangeAccessSupported = true
}
if infoRequest == nil || request.requestsAllDataToEndOfResource == true {
loadingRequest.dataRequest?.respond(with: data!)
}
loadingRequest.finishLoading()
} else {
print ("error \(error)")
loadingRequest.finishLoading(with: error)
}
}
}
task.resume()
return true
}