Decrypt Media Files in chunks and play via AVPlayer

问题

I have a mp4 video file which i am encrypting to save and decrypting to play via AVPlayer. Using CRYPTOSWIFT Library for encrypting/decrypting

Its working fine when i am decrypting whole file at once but my file is quite big and taking 100% CPU usage and lot of memory. So, I need to decrypt encrypted file in chunks. I tried to decrypt file in chunks but its not playing video as AVPlayer is not recognizing decrypted chunk data maybe data is not stored sequentially while encrypting file. I have tried chacha20, AES, AES.CTR & AES.CBC protocols to encrypt and decrypt files but to no avail.

extension PlayerController: AVAssetResourceLoaderDelegate {

   func resourceLoader(resourceLoader: AVAssetResourceLoader, shouldWaitForLoadingOfRequestedResource loadingRequest: AVAssetResourceLoadingRequest) -> Bool {
      let request = loadingRequest.request
      guard let path = request.URL?.path where request.URL?.scheme == Constants.customVideoScheme else { return true }
      if let contentRequest = loadingRequest.contentInformationRequest {
         do {
            let fileAttributes = try NSFileManager.defaultManager().attributesOfItemAtPath(path)
            if let fileSizeNumber = fileAttributes[NSFileSize] {
               contentRequest.contentLength = fileSizeNumber.longLongValue
            }
         } catch { }

         if fileHandle == nil {
            fileHandle = NSFileHandle(forReadingAtPath: (request.URL?.path)!)!
         }
         contentRequest.contentType = "video/mp4"
         contentRequest.byteRangeAccessSupported = true
      }

      if let data = decryptData(loadingRequest, path: path), dataRequest = loadingRequest.dataRequest {
         dataRequest.respondWithData(data)
         loadingRequest.finishLoading()
         return true
      }
      return true
   }

   func decryptData(loadingRequest: AVAssetResourceLoadingRequest, path: String) -> NSData? {
      print("Current OFFSET: \(loadingRequest.dataRequest?.currentOffset)")
      print("requested OFFSET: \(loadingRequest.dataRequest?.requestedOffset)")
      print("Current Length: \(loadingRequest.dataRequest?.requestedLength)")
      if loadingRequest.contentInformationRequest != nil {
         var data = fileHandle!.readDataOfLength((loadingRequest.dataRequest?.requestedLength)!)
         fileHandle!.seekToFileOffset(0)
         data = decodeVideoData(data)!
         return data
      } else {
         fileHandle?.seekToFileOffset(UInt64((loadingRequest.dataRequest?.currentOffset)!))
         let data = fileHandle!.readDataOfLength((loadingRequest.dataRequest?.requestedLength)!)
// let data = fileHandle!.readDataOfLength(length!) ** When I use this its not playing video but play fine when try with requestedLength **
         return decodeVideoData(data)
      }
   }
}

Decode code to decode nsdata :

 func decodeVideoData(data: NSData) -> NSData? {
      if let cha = ChaCha20(key: Constants.Encryption.SecretKey, iv: Constants.Encryption.IvKey) {
         let decrypted: NSData = try! data.decrypt(cha)
         return decrypted
      }
      return nil
   }

I need help regarding this issue, Kindly guide me to the right way to achieve this.

来源：https://stackoverflow.com/questions/37014686/decrypt-media-files-in-chunks-and-play-via-avplayer

标签

ios

swift

cryptography

swift2

avplayer