If you are working on OS X only I would stick with the QTKit APIs because they are much higher level and generally easier to work with.

The general gist of what you want to do is:

1. Step Through each frame in a movie
2. Get a image representation for the current frame
3. Save the current frame's image to a file on disk

To step through the frames in a QuickTime movie, you can use the QTMovie class in QTKit to do this as follows:

- (void)dumpFramesWithMovie:(QTMovie*)movie toFolder:(NSString*)folderPath
{
    [movie setIdling:NO]; // Don't idle the movie

    [movie gotoEnd];
    QTTime endTime = [movie currentTime];

    [movie gotoBeginning];

    // Number of frames counted so far
    unsigned long numFrames = 0;

    // Turn off the Movie's looping so we are quaranteed to stop
    [movie setAttribute:[NSNumber numberWithBool:NO] forKey:QTMovieLoopsAttribute];

    // Construct a Dictionary of to use when reading frames from a movie
    NSMutableDictionary *attributes = [NSMutableDictionary dictionary];
    [attributes setObject:QTMovieFrameImageTypeNSImage forKey:QTMovieFrameImageType];    
    while (true)
    {
        QTTime curTime = [movie currentTime];
        if (QTTimeCompare(curTime, endTime) == NSOrderedSame)
        {
            // Reached end of file
            break;
        }

        // Get the Current Frame as an NSImage
        NSImage* image = [movie frameImageAtTime:curTime 
                                  withAttributes:attributes error:nil];

        // Get the bitmap representation of this image
        // NOTE: This code assumes the first image representation is a NSBitmapImageRep, which is true
        // by default in OS X 10.5 and later.  
        // Production code should do error checking here.
        NSBitmapImageRep *bitmap = [[image representations] objectAtIndex: 0];

        // Construct a filename based upon the folder path and number of frames read so far
        NSString* fileName = [NSString stringWithFormat:@"%@/frame%d.png", folderPath, numFrames];

        // Get an PNG representation of this file
        NSData *data = [bitmap representationUsingType: NSPNGFileType
                                            properties: nil];

        // Write to disk
        [data writeToFile: fileName
               atomically: NO];

        // Step to the next Frame
        [movie stepForward];
        numFrames++;
    }

    [movie gotoBeginning];
}
@end

This code compiles but has not been fully tested.

One caveat with this approach is that MPEG-1 files will not decode properly on OS X 10.5 and earlier. This has been fixed as of 10.6 as far as I know. Also, if are writing a Windows application, you'll need to use the lower lever Quicktime-C APIs.

Be sure to check the following reference pages while working on this:

• QTKit Application Programming Guide
• QTKit Frequently Asked Questions
• QTMovie Class Reference
• Quickies for NSImage
• NSBitmapImageRep Reference
• NSImage Reference

If you can't get this to work in your version of QuickTime you'll need another tool.

VLC [Freeware] can snapshot either on the fly or when paused with Opt ⌥ Cmd ⌘ S & generally runs rings round Quicktime as a player.

Note, because of its popularity, there are scam sites primed for unsuspecting prey.
VLC's domain is videolan.org