ios - 响应没有 'Content-Lenght' header 时的 AVURLAsset

Question

我的 iOS 应用程序使用 AVPlayer 从我的服务器播放流式音频并将其存储在设备上。
我实现了 AVAssetResourceLoaderDelegate，所以我可以拦截流。我将我的方案(从 http 更改为假方案，以便调用 AVAssetResourceLoaderDelegate 方法:
func resourceLoader(_ resourceLoader: AVAssetResourceLoader, shouldWaitForLoadingOfRequestedResource loadingRequest: AVAssetResourceLoadingRequest) -> Bool
我遵循了本教程:

http://blog.jaredsinclair.com/post/149892449150/implementing-avassetresourceloaderdelegate-a

在那里，我把原来的方案放回去，并创建一个从服务器提取音频的 session 。当我的服务器提供 Content-Length 时，一切正常。 (音频文件的大小，以字节为单位)流式音频文件的 header 。

但有时我会在无法提前提供其长度的情况下流式传输音频文件(比如直播播客流)。在这种情况下，AVURLAsset 将长度设置为 -1并失败:
"Error Domain=AVFoundationErrorDomain Code=-11849 \"Operation Stopped\" UserInfo={NSUnderlyingError=0x61800004abc0 {Error Domain=NSOSStatusErrorDomain Code=-12873 \"(null)\"}, NSLocalizedFailureReason=This media may be damaged., NSLocalizedDescription=Operation Stopped}"
我无法绕过这个错误。我试图走一个hacky方式，提供假的Content-Length: 999999999 ，但在这种情况下，一旦下载了整个音频流，我的 session 就会失败，并显示:
Loaded so far: 10349852 out of 99999999 The request timed out. //Audio file got downloaded, its size is 10349852 //AVPlayer tries to get the next chunk and then fails with request times out
有没有人遇到过这个问题？

附言如果我保留原件 http AVURLAsset 中的方案，AVPlayer 知道如何处理这个方案，所以它可以很好地播放音频文件(即使没有 Content-Length )，我不知道它是如何做到的，没有失败。此外，在这种情况下，我的 AVAssetResourceLoaderDelegate 从未使用过，因此我无法截取音频文件的内容并将其复制到本地存储。

这是实现:

import AVFoundation

@objc protocol CachingPlayerItemDelegate {

    // called when file is fully downloaded
    @objc optional func playerItem(playerItem: CachingPlayerItem, didFinishDownloadingData data: NSData)

    // called every time new portion of data is received
    @objc optional func playerItemDownloaded(playerItem: CachingPlayerItem, didDownloadBytesSoFar bytesDownloaded: Int, outOf bytesExpected: Int)

    // called after prebuffering is finished, so the player item is ready to play. Called only once, after initial pre-buffering
    @objc optional func playerItemReadyToPlay(playerItem: CachingPlayerItem)

    // called when some media did not arrive in time to continue playback
    @objc optional func playerItemDidStopPlayback(playerItem: CachingPlayerItem)

    // called when deinit
    @objc optional func playerItemWillDeinit(playerItem: CachingPlayerItem)

}

extension URL {

    func urlWithCustomScheme(scheme: String) -> URL {
        var components = URLComponents(url: self, resolvingAgainstBaseURL: false)
        components?.scheme = scheme
        return components!.url!
    }

}

class CachingPlayerItem: AVPlayerItem {

    class ResourceLoaderDelegate: NSObject, AVAssetResourceLoaderDelegate, URLSessionDelegate, URLSessionDataDelegate, URLSessionTaskDelegate {

        var playingFromCache = false
        var mimeType: String? // is used if we play from cache (with NSData)

        var session: URLSession?
        var songData: NSData?
        var response: URLResponse?
        var pendingRequests = Set<AVAssetResourceLoadingRequest>()
        weak var owner: CachingPlayerItem?

        //MARK: AVAssetResourceLoader delegate

        func resourceLoader(_ resourceLoader: AVAssetResourceLoader, shouldWaitForLoadingOfRequestedResource loadingRequest: AVAssetResourceLoadingRequest) -> Bool {

            if playingFromCache { // if we're playing from cache
                // nothing to do here
            } else if session == nil { // if we're playing from url, we need to download the file
                let interceptedURL = loadingRequest.request.url!.urlWithCustomScheme(scheme: owner!.scheme!).deletingLastPathComponent()
                startDataRequest(withURL: interceptedURL)
            }

            pendingRequests.insert(loadingRequest)
            processPendingRequests()
            return true
        }

        func startDataRequest(withURL url: URL) {
            let request = URLRequest(url: url)
            let configuration = URLSessionConfiguration.default
            configuration.requestCachePolicy = .reloadIgnoringLocalAndRemoteCacheData
            configuration.timeoutIntervalForRequest = 60.0
            configuration.timeoutIntervalForResource = 120.0
            session = URLSession(configuration: configuration, delegate: self, delegateQueue: nil)
            let task = session?.dataTask(with: request)
            task?.resume()
        }

        func resourceLoader(_ resourceLoader: AVAssetResourceLoader, didCancel loadingRequest: AVAssetResourceLoadingRequest) {
            pendingRequests.remove(loadingRequest)
        }

        //MARK: URLSession delegate

        func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
            (songData as! NSMutableData).append(data)
            processPendingRequests()
            owner?.delegate?.playerItemDownloaded?(playerItem: owner!, didDownloadBytesSoFar: songData!.length, outOf: Int(dataTask.countOfBytesExpectedToReceive))
        }

        func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive response: URLResponse, completionHandler: @escaping (URLSession.ResponseDisposition) -> Void) {
            completionHandler(URLSession.ResponseDisposition.allow)
            songData = NSMutableData()
            self.response = response
            processPendingRequests()
        }

        func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError err: Error?) {
            if let error = err {
                print(error.localizedDescription)
                return
            }
            processPendingRequests()
            owner?.delegate?.playerItem?(playerItem: owner!, didFinishDownloadingData: songData!)
        }

        //MARK:

        func processPendingRequests() {
            var requestsCompleted = Set<AVAssetResourceLoadingRequest>()
            for loadingRequest in pendingRequests {
                fillInContentInforation(contentInformationRequest: loadingRequest.contentInformationRequest)
                let didRespondCompletely = respondWithDataForRequest(dataRequest: loadingRequest.dataRequest!)
                if didRespondCompletely {
                    requestsCompleted.insert(loadingRequest)
                    loadingRequest.finishLoading()
                }
            }
            for i in requestsCompleted {
                pendingRequests.remove(i)
            }
        }

        func fillInContentInforation(contentInformationRequest: AVAssetResourceLoadingContentInformationRequest?) {
            // if we play from cache we make no URL requests, therefore we have no responses, so we need to fill in contentInformationRequest manually
            if playingFromCache {
                contentInformationRequest?.contentType = self.mimeType
                contentInformationRequest?.contentLength = Int64(songData!.length)
                contentInformationRequest?.isByteRangeAccessSupported = true
                return
            }

            // have no response from the server yet
            if  response == nil {
                return
            }

            let mimeType = response?.mimeType
            contentInformationRequest?.contentType = mimeType
            if response?.expectedContentLength != -1 {
                contentInformationRequest?.contentLength = response!.expectedContentLength
                contentInformationRequest?.isByteRangeAccessSupported = true
            } else {
                contentInformationRequest?.isByteRangeAccessSupported = false
            }
        }

        func respondWithDataForRequest(dataRequest: AVAssetResourceLoadingDataRequest) -> Bool {

            let requestedOffset = Int(dataRequest.requestedOffset)
            let requestedLength = dataRequest.requestedLength
            let startOffset = Int(dataRequest.currentOffset)

            // Don't have any data at all for this request
            if songData == nil || songData!.length < startOffset {
                return false
            }

            // This is the total data we have from startOffset to whatever has been downloaded so far
            let bytesUnread = songData!.length - Int(startOffset)

            // Respond fully or whaterver is available if we can't satisfy the request fully yet
            let bytesToRespond = min(bytesUnread, requestedLength + Int(requestedOffset))
            dataRequest.respond(with: songData!.subdata(with: NSMakeRange(startOffset, bytesToRespond)))

            let didRespondFully = songData!.length >= requestedLength + Int(requestedOffset)
            return didRespondFully

        }

        deinit {
            session?.invalidateAndCancel()
        }

    }

    private var resourceLoaderDelegate = ResourceLoaderDelegate()
    private var scheme: String?
    private var url: URL!

    weak var delegate: CachingPlayerItemDelegate?

    // use this initializer to play remote files
    init(url: URL) {

        self.url = url

        let components = URLComponents(url: url, resolvingAgainstBaseURL: false)!
        scheme = components.scheme

        let asset = AVURLAsset(url: url.urlWithCustomScheme(scheme: "fakeScheme").appendingPathComponent("/test.mp3"))
        asset.resourceLoader.setDelegate(resourceLoaderDelegate, queue: DispatchQueue.main)
        super.init(asset: asset, automaticallyLoadedAssetKeys: nil)
        resourceLoaderDelegate.owner = self

        self.addObserver(self, forKeyPath: "status", options: NSKeyValueObservingOptions.new, context: nil)

        NotificationCenter.default.addObserver(self, selector: #selector(didStopHandler), name:NSNotification.Name.AVPlayerItemPlaybackStalled, object: self)

    }

    // use this initializer to play local files
    init(data: NSData, mimeType: String, fileExtension: String) {

        self.url = URL(string: "whatever://whatever/file.\(fileExtension)")

        resourceLoaderDelegate.songData = data
        resourceLoaderDelegate.playingFromCache = true
        resourceLoaderDelegate.mimeType = mimeType

        let asset = AVURLAsset(url: url)
        asset.resourceLoader.setDelegate(resourceLoaderDelegate, queue: DispatchQueue.main)

        super.init(asset: asset, automaticallyLoadedAssetKeys: nil)
        resourceLoaderDelegate.owner = self

        self.addObserver(self, forKeyPath: "status", options: NSKeyValueObservingOptions.new, context: nil)

        NotificationCenter.default.addObserver(self, selector: #selector(didStopHandler), name:NSNotification.Name.AVPlayerItemPlaybackStalled, object: self)

    }

    func download() {
        if resourceLoaderDelegate.session == nil {
            resourceLoaderDelegate.startDataRequest(withURL: url)
        }
    }

    override init(asset: AVAsset, automaticallyLoadedAssetKeys: [String]?) {
        fatalError("not implemented")
    }

    // MARK: KVO
    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        delegate?.playerItemReadyToPlay?(playerItem: self)
    }

    // MARK: Notification handlers

    func didStopHandler() {
        delegate?.playerItemDidStopPlayback?(playerItem: self)
    }

    // MARK:

    deinit {
        NotificationCenter.default.removeObserver(self)
        removeObserver(self, forKeyPath: "status")
        resourceLoaderDelegate.session?.invalidateAndCancel()
        delegate?.playerItemWillDeinit?(playerItem: self)
    }

}

Answer 1

您无法处理这种情况，因为对于 iOS，此文件已损坏，因为标题不正确。系统认为您将播放常规音频文件，但它没有关于它的所有信息。您不知道音频持续时间是多少，只有当您有直播时。 iOS 上的直播是使用 HTTP 直播流协议(protocol)完成的。
您的 iOS 代码是正确的。您必须修改您的后端并为直播音频提供 m3u8 播放列表，然后 iOS 将接受它作为直播流，音频播放器将开始播放轨道。

一些相关信息可以找到here .作为一个在流媒体音频/视频方面经验丰富的 iOS 开发人员，我可以告诉你，播放直播/VOD 的代码是一样的。