//videoURL:本地视频路径    time：用来控制视频播放的时间点图片截取

-(UIImage*) thumbnailImageForVideo:(NSURL *)videoURL atTime:(NSTimeInterval)time {

  AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:videoURL options:nil];

  NSParameterAssert(asset);

  AVAssetImageGenerator *assetImageGenerator =[[AVAssetImageGenerator alloc] initWithAsset:asset];

  assetImageGenerator.appliesPreferredTrackTransform = YES;

  assetImageGenerator.apertureMode = AVAssetImageGeneratorApertureModeEncodedPixels;

  CGImageRef thumbnailImageRef = NULL;

  CFTimeInterval thumbnailImageTime = time;

  NSError *thumbnailImageGenerationError = nil;

  thumbnailImageRef = [assetImageGenerator copyCGImageAtTime:CMTimeMake(thumbnailImageTime, 60)actualTime:NULL error:&thumbnailImageGenerationError];

  if(!thumbnailImageRef)

      NSLog(@"thumbnailImageGenerationError %@",thumbnailImageGenerationError);  

  UIImage*thumbnailImage = thumbnailImageRef ? [[UIImage alloc]initWithCGImage: thumbnailImageRef] : nil;  

  return thumbnailImage;

}

/// 获取本地video的封面截图

    ///

    /// - Parameter url: <#url description#>

    /// - Returns: <#return value description#>

    func getVideoFengMian(url:String) -> UIImage {

        if url.isEmpty {

            //默认封面图

            return UIImage(named: "screenVideo")!

        }

        let aset = AVURLAsset(url: URL(fileURLWithPath: url), options: nil)

        let assetImg = AVAssetImageGenerator(asset: aset)

        assetImg.appliesPreferredTrackTransform = true

        assetImg.apertureMode = AVAssetImageGeneratorApertureModeEncodedPixels

        do{

            let cgimgref = try assetImg.copyCGImage(at: CMTime(seconds: , preferredTimescale: ), actualTime: nil)

            return UIImage(cgImage: cgimgref)           

        }catch{

            return UIImage(named: "screenVideo")!

        }

    }