DownloadingFileAsset

AVAsset subclass aimed to work with external cache services

DownloadingFileAsset is a subclass of AVAsset. It allows you to read or play a media file under downloading, more resillient with narrow network than the original.

Motivation

Media files are getting larger. It's normal to download them from the Internet. For better UX, apps don't wait to download entire the media but start consuming as soon as possible in the middle of downloading. But:

• When I used AVURLAsset(url: localDiskURL), it read only available data that exists in the local disk at that moment and quittted reading.
• I could use AVURLAsset(url: remoteURL) instead, but it means the user would download the file twice.

Apple provides the custom resource downloading mechanism what works with AVURLAsset and it will be a help for the situation.
DownloadingFileAsset is a compileed implementation of it.

Usage

Instantiate DownloadingFileAsset with local file URL and its expected file size:

let asset = DownloadingFileAsset(localFileURL: downloadCacheURL,
                                 expectedFileSize: expectedFileSize)

It is supporsed to be available... but not yet. Any asset reading process still ends with just locally available data.

We needs a workaround for progressive reading:

// FIXME this is a workaround
self.playerItem = AVPlayerItem(asset: asset)     // both need a strong reference
self.player = AVPlayer(playerItem: playerItem!)

Note: for completely downloaded file, use AVAsset or any other classes instead.

Error notifications

Errors will be notified via NotificationCenter. To receive them, you can code like:

NotificationCenter.default.addObserver(self,
                                       selector: #selector(downloadError),
                                       name: .AssetFileLoaderDelegateFailedToOpenFile,
                                       object: asset.resourceLoader.delegate)
NotificationCenter.default.addObserver(self,
                                       selector: #selector(downloadError),
                                       name: .AssetFileLoaderDelegateReadTimeout,
                                       object: asset.resourceLoader.delegate)

// ...

@objc func downloadError(_ notification: Notification) {
  if let error = notification.userInfo?[AssetFileLoaderDelegateErrorKey] as? Error {
    // manage the error
  }
}

Example

To run the example project, clone the repo, and run pod install from the Example directory first.

Requirements

iOS 9.3+

Installation

DownloadingFileAsset is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod 'DownloadingFileAsset'

Author

HANAI tohru, [email protected]

License

DownloadingFileAsset is available under the MIT license. See the LICENSE file for more info.