Obtaining the first frame video image and displayed by imageView

UIImageView displays the first frame of the video picture

引入头文件
#import <AVFoundation/AVAssetImageGenerator.h>
#import <AVFoundation/AVAsset.h>
#import <AVFoundation/AVTime.h>


// 获取视频第一帧图片（异步加载数据）
-(void)getVideoPreViewImageURL:(NSURL *)path forImageView:(UIImageView *)imageView placeHolderImage:(UIImage *)placeHolder
{
    // 视频链接转MD5作为图片的名字
    NSString *name = [[path absoluteString] ms_MD5String];
    NSString *PATH = [NSString stringWithFormat:@"%@/Documents/videoFolder/%@.png",NSHomeDirectory(),name];
    UIImage *imagePath = [[UIImage alloc] initWithContentsOfFile:PATH];
    if (imagePath) {
        // 本地有缓存图片，加载本地图片并return
        imageView.image = imagePath;
        return;
    }else{
        // 本地没有缓存图片，先加载占位图
        imageView.image = placeHolder;
    }
    
    dispatch_group_t group = dispatch_group_create();
    __block UIImage *videoImage;
    dispatch_group_async(group, dispatch_get_global_queue(0, 0), ^{
        AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:path options:nil];
        AVAssetImageGenerator *assetGen = [[AVAssetImageGenerator alloc] initWithAsset:asset];
        
        assetGen.appliesPreferredTrackTransform = YES;
        CMTime time = CMTimeMakeWithSeconds(0.0, 2);
        NSError *error = nil;
        CMTime actualTime;
        CGImageRef image = [assetGen copyCGImageAtTime:time actualTime:&actualTime error:&error];
        videoImage = [[UIImage alloc] initWithCGImage:image];
        CGImageRelease(image);
        
        // 创建文件夹
        NSString *folder = [NSHomeDirectory() stringByAppendingPathComponent:@"/Documents/videoFolder"];
        [[NSFileManager defaultManager] createDirectoryAtPath:folder withIntermediateDirectories:NO attributes:nil error:nil];
        [UIImagePNGRepresentation(videoImage) writeToFile:PATH atomically:YES];
    });
    
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        // 主线程更新UI
        imageView.image = videoImage;
    });
}