iOS 獲取視訊圖片

/**
 * 擷取指定時間的視訊縮圖
 *
 * @param timeBySecond 時間點，單位：s
 */
- (UIImage *)thumbnailImageRequestWithVideoUrl:(NSURL *)videoUrl andTime:(CGFloat)timeBySecond
{
    AVURLAsset *urlAsset = [AVURLAsset assetWithURL:videoUrl];
    
    //根據AVURLAsset建立AVAssetImageGenerator
    AVAssetImageGenerator *imageGenerator = [AVAssetImageGenerator assetImageGeneratorWithAsset:urlAsset];
    /*截圖
     * requestTime:縮圖建立時間
     * actualTime:縮圖實際生成的時間
     */
    NSError *error = nil;
    CMTime requestTime = CMTimeMakeWithSeconds(timeBySecond, 10); //CMTime是表示電影時間資訊的結構體，第一個參數列示是視訊第幾秒，第二個參數列示每秒幀數.(如果要活的某一秒的第幾幀可以使用CMTimeMake方法)
    CMTime actualTime;
    CGImageRef cgImage = [imageGenerator copyCGImageAtTime:requestTime actualTime:&actualTime error:&error];
    if(error)
    {
        NSLog(@"擷取視訊縮圖時發生錯誤，錯誤資訊：%@", error.localizedDescription);
        return nil;
    }
    
    CMTimeShow(actualTime);
    UIImage *image = [UIImage imageWithCGImage:cgImage];
    CGImageRelease(cgImage);
    // 圖片旋轉 -- 這裡需要判斷是否需要使用
    UIImage *finalImage = [self rotateImage:image withOrientation:UIImageOrientationRight];
    return finalImage;
}

// 圖片旋轉
- (UIImage *)rotateImage:(UIImage *)image withOrientation:(UIImageOrientation)orientation
{
    long double rotate = 0.0;
    CGRect rect;
    float translateX = 0;
    float translateY = 0;
    float scaleX = 1.0;
    float scaleY = 1.0;
    
    switch (orientation)
    {
        case UIImageOrientationLeft:
            rotate = M_PI_2;
            rect = CGRectMake(0, 0, image.size.height, image.size.width);
            translateX = 0;
            translateY = -rect.size.width;
            scaleY = rect.size.width/rect.size.height;
            scaleX = rect.size.height/rect.size.width;
            break;
        case UIImageOrientationRight:
            rotate = 3 * M_PI_2;
            rect = CGRectMake(0, 0, image.size.height, image.size.width);
            translateX = -rect.size.height;
            translateY = 0;
            scaleY = rect.size.width/rect.size.height;
            scaleX = rect.size.height/rect.size.width;
            break;
        case UIImageOrientationDown:
            rotate = M_PI;
            rect = CGRectMake(0, 0, image.size.width, image.size.height);
            translateX = -rect.size.width;
            translateY = -rect.size.height;
            break;
        default:
            rotate = 0.0;
            rect = CGRectMake(0, 0, image.size.width, image.size.height);
            translateX = 0;
            translateY = 0;
            break;
    }
    
    UIGraphicsBeginImageContext(rect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    //做CTM變換
    CGContextTranslateCTM(context, 0.0, rect.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);
    CGContextRotateCTM(context, rotate);
    CGContextTranslateCTM(context, translateX, translateY);
    
    CGContextScaleCTM(context, scaleX, scaleY);
    //繪製圖片
    CGContextDrawImage(context, CGRectMake(0, 0, rect.size.width, rect.size.height), image.CGImage);
    
    UIImage *newPic = UIGraphicsGetImageFromCurrentImageContext();
    
    return newPic;
}