如何在视频保存到相册后使用MPMoviePlayerController播放本地视频

Question

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {

    NSURL *videoURL = [info objectForKey:UIImagePickerControllerMediaURL];


    //get the videoURL 
    NSString *tempFilePath = [videoURL path];


    if ( UIVideoAtPathIsCompatibleWithSavedPhotosAlbum(tempFilePath))
    {
      // Copy it to the camera roll.
      UISaveVideoAtPathToSavedPhotosAlbum(tempFilePath, self, @selector(video:didFinishSavingWithError:contextInfo:), tempFilePath);
    } 



    //NSURL *movieUrl = [NSURL fileURLWithPath:filePath];
    _videoPlayer = [[MPMoviePlayerController alloc] initWithContentURL:videoURL];
    _videoPlayer.view.frame = CGRectMake(kMarginWidth, kMarginWidth, kMPlayerWidth, kMPlayerHeight);

    // Here is where you set the control Style like fullscreen or embedded
    _videoPlayer.controlStyle = MPMovieControlStyleDefault;
    _videoPlayer.scalingMode = MPMovieScalingModeAspectFit;
    _videoPlayer.contentURL = videoURL; 

     self addSubview:_videoPlayer];

}

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但是视频播放器不会出现，只能在屏幕上显示“加载电影”几秒钟。

那么有些人可以告诉我如何播放保存的视频吗？或如何检索相册中已保存视频的路径？