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Assigning Core Graphics Images to Thumbnails

In some cases the simplest course for generating a thumbnail is to create a Core Graphics image rather than creating an image compatible with the I/O framework or drawing the image in a graphics context. For example, your generator might be using a framework that can directly provide a serialized version of the thumbnail image as a CGImage object. For this cases, you can create the Core Graphics image and then communicate that image to Quick Look by calling the QLThumbnailRequestSetImage function. The main difference between this function and QLThumbnailRequestSetImageWithData is that the latter function requires the image data to be in a format that is supported by the I/O framework.

Listing 8-1 illustrates approach, using methods of the QT Kit framework to get the poster frame of a movie as a Core Graphics image and setting that as the thumbnail for a movie file.

Listing 8-1 Creating and assigning a Core Graphics image

OSStatus GenerateThumbnailForURL(void *thisInterface, QLThumbnailRequestRef thumbnail, CFURLRef url, CFStringRef contentTypeUTI, CFDictionaryRef options, CGSize maxSize)

    NSError *theErr;

    QTMovie *theMovie = [QTMovie movieWithURL:(__bridge NSURL *)url error:&theErr];

    if (theMovie == nil) {

        if (theErr != nil) {

            NSLog(@"Couldn't load movie URL, error = %@", theErr);

        return noErr;

    [theMovie gotoPosterTime];

    QTTime mTime = [theMovie currentTime];

    NSDictionary *imgProp = [NSDictionary dictionaryWithObject:QTMovieFrameImageTypeCGImageRef forKey:QTMovieFrameImageType];

    CGImageRef theImage = (__bridge CGImageRef)[theMovie frameImageAtTime:mTime withAttributes:imgProp error:&theErr];

    if (theImage == nil) {

        if (theErr != nil) {

            NSLog(@"Couldn't create CGImageRef, error = %@", theErr);

        return noErr;

    QLThumbnailRequestSetImage(thumbnail, theImage, NULL);

    return noErr;

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