     カメラロールから古い順で10個のビデオを取り出し、リーダーをセットアップする
     */
     func setupAssets() {
-        weak var weakSelf = self
         let collections = PHAssetCollection.fetchAssetCollectionsWithType(.SmartAlbum, subtype:.SmartAlbumVideos, options: nil)
-        collections.enumerateObjectsUsingBlock { (collection, index, stop)  in
+        collections.enumerateObjectsUsingBlock { [unowned self] (collection, index, stop)  in
 
             let assets = PHAsset.fetchAssetsInAssetCollection(collection as PHAssetCollection, options: nil)
 

        // 注意点：
        // - このビデオトラックにはコンポジション上のビデオトラックを指定すること
        // - IOSurfaceで作成しなくても再生できるが、念のため付けておく
        let videoTracks = composition.tracksWithMediaType(AVMediaTypeVideo)
        var output = AVAssetReaderVideoCompositionOutput(videoTracks: videoTracks,
            videoSettings: [kCVPixelBufferPixelFormatTypeKey : kCVPixelFormatType_32BGRA,
                kCVPixelBufferIOSurfacePropertiesKey : [:]])
        output.videoComposition = videoComposition

                _ = PHImageManager.defaultManager().requestAVAssetForVideo(asset as PHAsset,
                    options:nil, resultHandler: { (avasset:AVAsset!, audioMix:AVAudioMix!, info) -> Void in
                        dispatch_async(dispatch_get_main_queue()) {
                            if self.readers.count < 10 {
                                let reader = self.buildAssetReader(avasset)
                                self.readers.append(reader!)
                                reader!.startReading()
                                NSLog("[\(index)] start reading")
                            } else {
