简洁易懂的ResourceLoaderDelegate实现AVPlayer缓存边播边下 iOS swift5 《一》

最近在研究ios Swift 的 AVPlayer 边下边播，在网上找了很多相关内容，实现起来都比较复杂，对于自己实现参照太难，经过我的不懈努力，和耗费了很多精力，终于找到了比较简单易懂的方法，现在分享给大家，希望可以给遇到相同的问题的小伙伴以启发 from lizhi荔枝

1.说明

本篇文章主要讲述 ios AVPlayer 通过 ResourceLoaderDelegate实现下载数据，下一遍文章再讲述数据存储等。

通过AVAssetResourceLoaderDelegate 实现变下边播，只需要下载一遍的流量就可以。

2.方案思路

AVAssetResourceLoaderDelegate
首先了解一下AVAssetResourceLoaderDelegate所在的层：

ResouceLoader层次图

其中核心类：

• AVAssetResourceLoader：这个类负责多媒体（音视频）二进制数据的加载（下载），然后回调给上层Asset,让视频播放。但是这个类作为AVURLAsset是只读属性，但是它允许下面这个代理去如何加载数据资源。

• AVAssetResourceLoaderDelegate：它是一个协议，那么任何实现了该协议的对象都可以充当AVAssetResourceLoader的代理来指示视频数据的加载，既然数据资源可以有开发人员自行加载然后再回填给播放器，那么缓存就可以有自己控制了，OK，这就是我们这个方案的思路。

• AVPlayer 和 ResourceLoader 的数据流交互如下

  
  
  11_副本.png

3. AVPlayer 通过ResourceLoader 下载需要实现的方法

a.通过自定义scheme来创建avplayer，并给AVURLAsset指定代理 (LZAVPlayer)

    private func preparePlayer() {
        guard let url = URL(string: mediaUrl) else {
            return
        }
        //下载
        var component = URLComponents(url: url, resolvingAgainstBaseURL: true)!
        component.scheme = "LZStream"
        let streamUrl: URL = component.url!
        let urlAssrt = AVURLAsset(url: streamUrl)
        videoResourceLoader = LZResourceLoader(originalURL: url)

        guard let resourceLoader = videoResourceLoader else {
            return
        }
        urlAssrt.resourceLoader.setDelegate(videoResourceLoader, queue: resourceLoader.resourceLoaderQueue)
       let playerItem = AVPlayerItem(asset: urlAssrt)
        if player == nil {
            player = AVPlayer(playerItem: playerItem)
        } else {
            player?.replaceCurrentItem(with: playerItem)
        }
    }

b.代理实现AVAssetResourceLoader的代理方法（SUResourceLoader对象）

// MARK: - AVAssetResourceLoaderDelegate
extension LZResourceLoader: AVAssetResourceLoaderDelegate {
    public func resourceLoader(_ resourceLoader: AVAssetResourceLoader, shouldWaitForLoadingOfRequestedResource loadingRequest: AVAssetResourceLoadingRequest) -> Bool {
        // 启动下载任务，同时保留loadingRequest
        if  videoDownload == nil{
            videoDownload = LZResourceDownloader(originalUrl: originalURL)
        }
        print("--[shouldWait]-- loadRequest = \(loadingRequest)")
        videoDownload?.addDownload(loadingRequest: loadingRequest)
        return true
    }
    public func resourceLoader(_ resourceLoader: AVAssetResourceLoader, didCancel loadingRequest: AVAssetResourceLoadingRequest) {
        print("-- resourceLoader|didCancel")
        videoDownload?.removeDownload(loadingRequest: loadingRequest)
    }
}

c.通过urlsession下载数据

   func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive response: URLResponse, completionHandler: @escaping (URLSession.ResponseDisposition) -> Void) {
        if let loadingRequest = self.loadingRequests.first {
            self.fillInContentInformationRequest(loadingRequest, from: response)
        }
        completionHandler(.allow)
    }
    
    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
        if let loadingRequest = self.loadingRequests.first {
            loadingRequest.dataRequest?.respond(with: data)
        }
    }
    
    func urlSession(_: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
        print("--[urlSession] didCompleteWithError ")
        if error != nil {
            if let loadingRequest = self.loadingRequests.first {
                loadingRequest.finishLoading(with: error)
            }
            
        }else {
            if let loadingRequest = self.loadingRequests.first {
                loadingRequest.finishLoading()
            }
        }
        self.loadingRequests.removeFirst()
        self.loadNextToLoadedResource()
    }

d.填充响应数据loadingRequest

的contentInformationRequest

    //填充请求
    func fillInContentInformationRequest(_ loadingRestst:AVAssetResourceLoadingRequest,from response:URLResponse) {
        var contentLength = Int64(0)
        var isByteRangeAccessSupported = true
        var contentType: String = ""
        
        guard let httpResponse = response as? HTTPURLResponse else {
            return
        }
        // 将headers的key都转换为小写
        var headers = [String: Any]()
        for key in httpResponse.allHeaderFields.keys {
            let lowercased = (key as! String).lowercased()
            headers[lowercased] = httpResponse.allHeaderFields[key]
        }
        isByteRangeAccessSupported = (headers["accept-ranges"] as? String) == "bytes"
        if let rangeText = headers["content-range"] as? String, let lengthText = rangeText.split(separator: "/").last {
            contentLength = Int64(lengthText)!
        }
        if let mimeType = response.mimeType,
           let aContentType = UTTypeCreatePreferredIdentifierForTag(kUTTagClassMIMEType, mimeType as CFString, nil)?.takeRetainedValue()
        {
            contentType = aContentType as String
        }
        
        loadingRestst.contentInformationRequest?.contentType = contentType
        loadingRestst.contentInformationRequest?.contentLength = contentLength
        loadingRestst.contentInformationRequest?.isByteRangeAccessSupported = isByteRangeAccessSupported
    }

e.填充data数据到loadingRequest （respondWithData）

func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
        if let loadingRequest = self.loadingRequests.first {
            loadingRequest.dataRequest?.respond(with: data)
        }
    }

f.如果完全响应了所需要的数据，则完成loadingRequest (finishLoading)

 func urlSession(_: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
        print("--[urlSession] didCompleteWithError ")
        if error != nil {
            if let loadingRequest = self.loadingRequests.first {
                loadingRequest.finishLoading(with: error)
            }
            
        }else {
            if let loadingRequest = self.loadingRequests.first {
                loadingRequest.finishLoading()
            }
        }
        self.loadingRequests.removeFirst()
        self.loadNextToLoadedResource()
    }

---

VIMediaCache 找到了 第三方库 很好的实现了该功能，可以直接用了， 高兴ing，

https://github.com/vitoziv/VIMediaCache

ZFPlayer 很好用的视频播放器 集成了 多种样式播放

https://github.com/renzifeng/ZFPlayer

代码地址 LZAVPlayer

知识需研究，码字很不易，请点赞支持，from 荔枝lizhi, ；转载请注明出处