我正在开发一个iOS应用，该应用可通过HLS播放经过FairPlay加密的音频，并支持下载和流式传输。在飞行模式下，我无法播放下载的内容。如果我在下载完成后从本地URL创建一个AVURLAsset，则asset.assetCache.isPlayableOffline返回NO，并且当我尝试以飞行模式玩游戏时，如果可以肯定，它仍然会尝试请求其中一个。 m3u8播放列表文件。
我的主播放列表如下：
#EXTM3U
# Created with Bento4 mp4-hls.py version 1.1.0r623
#EXT-X-VERSION:5
#EXT-X-SESSION-KEY:METHOD=SAMPLE-AES,URI="skd://url/to/key?KID=foobar",KEYFORMAT="com.apple.streamingkeydelivery",KEYFORMATVERSIONS="1"
# Media Playlists
#EXT-X-STREAM-INF:AVERAGE-BANDWIDTH=133781,BANDWIDTH=134685,CODECS="mp4a.40.2" media-1/stream.m3u8
#EXT-X-STREAM-INF:AVERAGE-BANDWIDTH=67526,BANDWIDTH=67854,CODECS="mp4a.40.2" media-2/stream.m3u8
流播放列表如下：
#EXTM3U
#EXT-X-VERSION:5
#EXT-X-PLAYLIST-TYPE:VOD
#EXT-X-TARGETDURATION:30
#EXT-X-MEDIA-SEQUENCE:0
#EXT-X-KEY:METHOD=SAMPLE-AES,URI="skd://url/to/key?KID=foobar",KEYFORMAT="com.apple.streamingkeydelivery",KEYFORMATVERSIONS="1"
#EXTINF:30.000181,
#EXT-X-BYTERANGE:470290@0
media.aac
# more segments...
#EXT-X-ENDLIST
下载资产：
AVURLAsset *asset = [AVURLAsset assetWithURL:myM3u8Url];
[asset.resourceLoader setDelegate:[FairPlayKeyManager instance] queue:[FairPlayKeyManager queue]];
asset.resourceLoader.preloadsEligibleContentKeys = YES;
AVAssetDownloadTask *task = [self.session assetDownloadTaskWithURLAsset:asset assetTitle:@"Track" assetArtworkData:imgData options:nil];
[task resume];
在委托人的URLSession:assetDownloadTask:didFinishDownloadingToURL:中：
self.downloadedPath = location.relativePath;
在委托人的URLSession:task:didCompleteWithError:中：
if (!error)
{
NSString *strUrl = [NSHomeDirectory() stringByAppendingPathComponent:self.downloadedPath];
NSURL *url = [NSURL fileURLWithPath:strUrl];
AVURLAsset *localAsset = [AVURLAsset assetWithURL:url];
if (!localAsset.assetCache.playableOffline)
NSLog(@"Oh no!"); //not playable offline
}
除了资产缓存报告无法离线播放之外，下载不会产生任何错误。但是，如果您切换到飞行模式并尝试播放下载的资产，它将正确地向资源加载器委托请求一个密钥（并且我使用的是持久密钥，因此可以在离线状态下正常工作），然后尝试请求media-1/stream.m3u8。
这里没有我要处理的陷阱吗？播放列表文件是否应该有所不同？我缺少的任务或资产上有一些财产吗？
答案 0 :(得分：1)
我认为在检查asset.assetCache.isPlayableOffline之前，您需要检查的东西很少。
func handlePersistableContentKeyRequest(keyRequest: AVPersistableContentKeyRequest) {
/*
The key ID is the URI from the EXT-X-KEY tag in the playlist (e.g. "skd://key65") and the
asset ID in this case is "key65".
*/
guard let contentKeyIdentifierString = keyRequest.identifier as? String,
let contentKeyIdentifierURL = URL(string: contentKeyIdentifierString),
let assetIDString = contentKeyIdentifierURL.host,
let assetIDData = assetIDString.data(using: .utf8)
else {
print("Failed to retrieve the assetID from the keyRequest!")
return
}
do {
let completionHandler = { [weak self] (spcData: Data?, error: Error?) in
guard let strongSelf = self else { return }
if let error = error {
keyRequest.processContentKeyResponseError(error)
strongSelf.pendingPersistableContentKeyIdentifiers.remove(assetIDString)
return
}
guard let spcData = spcData else { return }
do {
// Send SPC to Key Server and obtain CKC
let ckcData = try strongSelf.requestContentKeyFromKeySecurityModule(spcData: spcData, assetID: assetIDString)
let persistentKey = try keyRequest.persistableContentKey(fromKeyVendorResponse: ckcData, options: nil)
try strongSelf.writePersistableContentKey(contentKey: persistentKey, withContentKeyIdentifier: assetIDString)
/*
AVContentKeyResponse is used to represent the data returned from the key server when requesting a key for
decrypting content.
*/
let keyResponse = AVContentKeyResponse(fairPlayStreamingKeyResponseData: persistentKey)
/*
Provide the content key response to make protected content available for processing.
*/
keyRequest.processContentKeyResponse(keyResponse)
let assetName = strongSelf.contentKeyToStreamNameMap.removeValue(forKey: assetIDString)!
if !strongSelf.contentKeyToStreamNameMap.values.contains(assetName) {
NotificationCenter.default.post(name: .DidSaveAllPersistableContentKey,
object: nil,
userInfo: ["name": assetName])
}
strongSelf.pendingPersistableContentKeyIdentifiers.remove(assetIDString)
} catch {
keyRequest.processContentKeyResponseError(error)
strongSelf.pendingPersistableContentKeyIdentifiers.remove(assetIDString)
}
}
// Check to see if we can satisfy this key request using a saved persistent key file.
if persistableContentKeyExistsOnDisk(withContentKeyIdentifier: assetIDString) {
let urlToPersistableKey = urlForPersistableContentKey(withContentKeyIdentifier: assetIDString)
guard let contentKey = FileManager.default.contents(atPath: urlToPersistableKey.path) else {
// Error Handling.
pendingPersistableContentKeyIdentifiers.remove(assetIDString)
/*
Key requests should never be left dangling.
Attempt to create a new persistable key.
*/
let applicationCertificate = try requestApplicationCertificate()
keyRequest.makeStreamingContentKeyRequestData(forApp: applicationCertificate,
contentIdentifier: assetIDData,
options: [AVContentKeyRequestProtocolVersionsKey: [1]],
completionHandler: completionHandler)
return
}
/*
Create an AVContentKeyResponse from the persistent key data to use for requesting a key for
decrypting content.
*/
let keyResponse = AVContentKeyResponse(fairPlayStreamingKeyResponseData: contentKey)
// Provide the content key response to make protected content available for processing.
keyRequest.processContentKeyResponse(keyResponse)
return
}
let applicationCertificate = try requestApplicationCertificate()
keyRequest.makeStreamingContentKeyRequestData(forApp: applicationCertificate,
contentIdentifier: assetIDData,
options: [AVContentKeyRequestProtocolVersionsKey: [1]],
completionHandler: completionHandler)
} catch {
print("Failure responding to an AVPersistableContentKeyRequest when attemping to determine if key is already available for use on disk.")
}
}
答案 1 :(得分：1)
事实证明，这是因为我正在从中下载音频的URL（例如https://mywebsite.com/path/to/master.m3u8重定向到CDN URL（https://my.cdn/other/path/to/master.m3u8）。{{1 }}簿记，以至于当我尝试离线播放生成的下载文件时，它认为它需要网络中的更多文件。我将其归档为Radar43285278。我通过手动向AVAssetDownloadTask请求来解决此问题相同的URL，然后为HEAD提供最终的重定向URL。