         return nil
     }
 
-    private func _prepareNextAssetReader(initial: AVAsset? = nil, atTime time: CMTime = kCMTimeZero) {
+    private func _prepareNextAssetReaders(initial: AVAsset? = nil, atTime time: CMTime = kCMTimeZero) {
         let lock = ScopedLock(self)
 
         // 読み込み済みリーダーの数が上限になっていれば何もしない

    :returns: アセット列におけるインデックスとシーク位置のタプル
    */
    private func _getAssetInfoForPosition(position: Float)
        -> (index:Int, timeStamp:CMTime)?
    {
        let lock = ScopedLock(self)


                    _currentPresentationTimestamp = kCMTimeZero
                    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0)) {
                        [unowned self] in
                        self._prepareNextAssetReaders()
                    }
                }
            case .Completed:
