获取网络视频或本地视频的第一帧图片

+ (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;  

}