Question

我正在开发一个iPhone应用程序，用于将视频文件上传到特定平台，我真正喜欢的一个功能就是能够为同一个视频呈现十个不同的缩略图，供用户使用选择。

问题是，ALAsset只提供缩略图方法，它只返回默认缩略图。我已经阅读了ALAssetRepresentation和ALAsset文档，但我似乎无法找到一种方法来获取特定时间戳的缩略图。

我想一个选择是使用类似于libav的东西来获取缩略图，但这似乎有点＆＃34;在顶部＆＃34;对于像这样的事情。任何人都可以帮我这个吗？

最好的问候，
尼克

Answer 1

我认为这会对你有所帮助你也可以通过这个提示看到 Video File thumbnail timestamp missing in ALAsset

{

  if ([theAsset valueForProperty:ALAssetPropertyType] == ALAssetTypeVideo) {

        // Black semi-transparent background at the bottom of the item
        CGRect containerFrame = CGRectMake(0, frame.size.height - AGIPC_ITEM_HEIGHT, frame.size.width, AGIPC_ITEM_HEIGHT);
        UIView *containerForMovieInfo = [[[UIView alloc] initWithFrame:containerFrame] autorelease];
        containerForMovieInfo.backgroundColor = [UIColor blackColor];
        containerForMovieInfo.alpha = 0.7f;

        // Movie icon on left side
        CGRect movieFrame = CGRectMake(4, 60, 26, 15);
        UIImageView *movieImageView = [[[UIImageView alloc] initWithFrame:movieFrame] autorelease];
        if (IS_IPAD()) {
            movieImageView.image = [UIImage imageNamed:@"AGIPC-Movie-iPad"];
        } else {
            movieImageView.image = [UIImage imageNamed:@"AGIPC-Movie-iPhone"];
        }
        [containerForMovieInfo addSubview:movieImageView];

        // Movie duration on right side
        if ([theAsset valueForProperty:ALAssetPropertyDuration] != ALErrorInvalidProperty) {
            NSDateFormatter *formatter = [[[NSDateFormatter alloc] init] autorelease];
            [formatter setDateFormat:@"mm:ss"];
            CGRect durationFrame = CGRectMake(frame.size.width - 26 - 4, 60, 26, 15);
            UILabel *durationView = [[[UILabel alloc] initWithFrame:durationFrame] autorelease];
            durationView.backgroundColor = [UIColor clearColor];
            durationView.textColor = [UIColor whiteColor];
            durationView.text = [formatter stringFromDate:[NSDate dateWithTimeIntervalSince1970:[[theAsset valueForProperty:ALAssetPropertyDuration] doubleValue]]];
            durationView.font = [UIFont systemFontOfSize:10];
            [containerForMovieInfo addSubview:durationView];
        }

        [self addSubview:containerForMovieInfo];
    }

}

最后但同样重要的是，您必须自己创建相机的图像。

Answer 2

// Get URL from ALAsset* asset:
NSURL* assetURL = [asset valueForProperty:ALAssetPropertyAssetURL];

// Create AVURLAsset using this URL (assetOptions is optional):
NSDictionary* assetOptions = nil;
// assetOptions = @{AVURLAssetPreferPreciseDurationAndTimingKey : @(YES)};
AVAsset* avAsset = [[AVURLAsset alloc] initWithURL:assetURL options:assetOptions];

// Create generator:
AVAssetImageGenerator* generator = [[AVAssetImageGenerator alloc] initWithAsset:avAsset];
generator.appliesPreferredTrackTransform = YES;

// Create array with CMTimes of thumbnails using your own logic.
// (Use +(NSValue*)valueWithCMTime:(CMTime)time to add CMTime in array).
NSArray* times = [self generateThumbnailTimesForVideo:avAsset];

// Generate thumbnail images asynchronously:
[generator generateCGImagesAsynchronouslyForTimes:times
                                completionHandler:^(CMTime requestedTime,
                                                    CGImageRef image,
                                                    CMTime actualTime,
                                                    AVAssetImageGeneratorResult result,
                                                    NSError* error)
    {
        // This block is performed for each CMTime in times array.
        UIImage* thumbnail = [[UIImage alloc] initWithCGImage:image];
    }
];

随时获取缩略图的同步方法是

// PS: SYNC method:
CGImageRef imgRef = [generator copyCGImageAtTime:time actualTime:NULL error:&error];
UIImage* thumbnail = [[UIImage alloc] initWithCGImage:image];

AL在特定时间戳处设置缩略图

2 个答案: