ios获取视频宽高比分辨率以及旋转角度

AVAsset *asset = [AVAsset assetWithURL:url];  
       NSArray *tracks = [asset tracksWithMediaType:AVMediaTypeVideo];  
       if([tracks count] > 0) {  
           AVAssetTrack *videoTrack = [tracks objectAtIndex:0];  
           CGAffineTransform t = videoTrack.preferredTransform;//这里的矩阵有旋转角度，转换一下便可  
           NSLog(@"=====hello  width:%f===height:%f",videoTrack.naturalSize.width,videoTrack.naturalSize.height);//宽高