Getting AppleScript return value in Obj-C

I'm using some AppleScript in my Obj-C cocoa project to control QuickTime player (play, pause, stop, jog forward and back etc.) with great success, though my knowledge of AppleScript is very limited. However, what I want most of all is the movie's 'Current Time' offset to convert into time-stamps for writing a subtitle script.

The following simple method shows the precise current position in (float) seconds in a dialog, but I'd really like the AppleScript to return me a variable that I can use in the rest of app. How could I modify the code below to do that? Is it even possible to access this value? Thanks a million in advance :-)

-(IBAction)currentPlayTime:(id)sender
{
    NSString *scriptString=[NSString stringWithFormat:
        // get time of current frame... (works perfectly)!
        @"tell application \"QuickTime Player\"\n"
            @"set timeScale to 600\n"
            @"set curr_pos to current time of movie 1/timeScale\n"
            @"display dialog curr_pos\n" // ...not in a practical form to use
        @"end tell\n"];

    NSDictionary *errorDict= nil;
    NSAppleScript *appleScriptObject=[[NSAppleScript alloc] initWithSource:scriptString];
    NSAppleEventDescriptor *eventDescriptor=[appleScriptObject executeAndReturnError:   &errorDict];
    // handle any errors here (snipped for brevity)
    [appleScriptObject release]; // can I retain this?
}