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iPhone SDK中的视频网址或数据中获取缩略图

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有大约5-10秒的延迟.反正我是否可以提高此代码的速度并更快地生成缩略图？

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.

+ (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;
}