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()
}
待续....
代码地址 LZAVPlayer
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