获取视频文件第一帧图片

+ (UIImage*) thumbnailImageForVideo:(NSString *)videoPath
{
    
    if(videoPath.length ==
0)
    {
        return
nil;
    }
    
    NSURL *videoURL = [NSURL
fileURLWithPath:videoPath];
    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 =
0;  
    NSError *thumbnailImageGenerationError =
nil;  
    thumbnailImageRef = [assetImageGenerator
copyCGImageAtTime:CMTimeMake(thumbnailImageTime,
15) actualTime:NULL
error:&thumbnailImageGenerationError];  

     
    
    UIImage *thumbnailImage = thumbnailImageRef ? [[UIImage
alloc] initWithCGImage:thumbnailImageRef] :
nil;
    //NSData *imageData = UIImagePNGRepresentation(thumbnailImage);
CGImageRelease(thumbnailImageRef);
    return thumbnailImage;
}