从视频创建缩略图 - 提高速度性能 - AVAsset - iPhone.

Question

我正在使用基于以下线程中的代码的代码来生成视频缩略图：

从视频网址获取缩略图或 iPhone SDK 中的数据

我的代码如下：

if (selectionType == kUserSelectedMedia) {
    NSURL * assetURL = [info objectForKey:UIImagePickerControllerReferenceURL];
    AVURLAsset *asset=[[AVURLAsset alloc] initWithURL:assetURL options:nil];
    AVAssetImageGenerator *generator = [[AVAssetImageGenerator alloc] initWithAsset:asset];
    generator.appliesPreferredTrackTransform=TRUE;
    [asset release];
    CMTime thumbTime = CMTimeMakeWithSeconds(0,30);
    //NSLog(@"Starting Async Queue");
    AVAssetImageGeneratorCompletionHandler handler = ^(CMTime requestedTime, CGImageRef im, CMTime actualTime, AVAssetImageGeneratorResult result, NSError *error){
        if (result != AVAssetImageGeneratorSucceeded) {
            NSLog(@"couldn't generate thumbnail, error:%@", error);
        }
        //NSLog(@"Updating UI");
        selectMediaButton.hidden = YES;
        selectedMedia.hidden = NO;
        cancelMediaChoiceButton.hidden = NO;
        whiteBackgroundMedia.hidden = NO;
        //Convert CGImage thumbnail to UIImage.
        UIImage * thumbnail = [UIImage imageWithCGImage:im];
        int checkSizeW = thumbnail.size.width;
        int checkSizeH = thumbnail.size.height;
        NSLog(@"Image width is %d", checkSizeW);
        NSLog(@"Image height is %d", checkSizeH);
        if (checkSizeW >=checkSizeH) {
            //This is a landscape image or video.
            NSLog(@"This is a landscape image - will resize automatically");
        }
        if (checkSizeH >=checkSizeW) {
            //This is a portrait image or video.
            selectedIntroHeight = thumbnail.size.height;
        }
        //Set the image once resized.
        selectedMedia.image = thumbnail;
        //Set out confirm button BOOL to YES and check if we need to display confirm button.
        mediaReady = YES;
        [self checkIfConfirmButtonShouldBeDisplayed];
        //[button setImage:[UIImage imageWithCGImage:im] forState:UIControlStateNormal];
        //thumbImg=[[UIImage imageWithCGImage:im] retain];
        [generator release];
    };
    CGSize maxSize = CGSizeMake(320, 180);
    generator.maximumSize = maxSize;
    [generator generateCGImagesAsynchronouslyForTimes:[NSArray arrayWithObject:[NSValue valueWithCMTime:thumbTime]] completionHandler:handler];
}
}

问题是生成缩略图图像时有大约 5-10 秒的延迟。无论如何，我可以提高此代码的速度并更快地生成缩略图吗？

谢谢。

Answer 1

这是一个通用代码，您应该只传递媒体文件的路径并将比率设置为 0 到 1.0 之间。

+ (UIImage*)previewFromFileAtPath:(NSString*)path ratio:(CGFloat)ratio
{
    AVAsset *asset = [AVURLAsset assetWithURL:[NSURL fileURLWithPath:path]];
    AVAssetImageGenerator *imageGenerator = [[AVAssetImageGenerator alloc]initWithAsset:asset];
    CMTime duration = asset.duration;
    CGFloat durationInSeconds = duration.value / duration.timescale;
    CMTime time = CMTimeMakeWithSeconds(durationInSeconds * ratio, (int)duration.value);
    CGImageRef imageRef = [imageGenerator copyCGImageAtTime:time actualTime:NULL error:NULL];
    UIImage *thumbnail = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);
    return thumbnail;
}

Answer 2

Swift 解决方案：

func previewImageForLocalVideo(url:NSURL) -> UIImage?
{
    let asset = AVAsset(URL: url)
    let imageGenerator = AVAssetImageGenerator(asset: asset)
    imageGenerator.appliesPreferredTrackTransform = true
    var time = asset.duration
    //If possible - take not the first frame (it could be completely black or white on camara's videos)
    time.value = min(time.value, 2)
    do {
        let imageRef = try imageGenerator.copyCGImageAtTime(time, actualTime: nil)
        return UIImage(CGImage: imageRef)
    }
    catch let error as NSError
    {
        print("Image generation failed with error (error)")
        return nil
    }
}