In-memory mime-type detection with Cocoa (OS X)?

NSData *movieData = ...read from memory...;
QTDataReference *movieDataReference = [[QTDataReference alloc] initWithReferenceToData:movieData name:fileName MIMEType:@"video/x-m4v"];
QTMovie *mov = [QTMovie movieWithDataReference:movieDataReference error:&err];

- (NSString*)mimeTypeForExtension:(NSString*)ext {

    CFStringRef UTI = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension,(CFStringRef)ext,NULL);
    return NSMakeCollectable(UTTypeCopyPreferredTagWithClass((CFStringRef)UTI,kUTTagClassMIMEType));
}

-(NSString*)mimeTypeForExtension:(NSString*)ext
{
    NSAssert( ext, @"Extension cannot be nil" );
    NSString* mimeType = nil;

    CFStringRef UTI = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension,
    	(CFStringRef)ext, NULL);
    if( !UTI ) return nil;

    CFStringRef registeredType = UTTypeCopyPreferredTagWithClass(UTI, kUTTagClassMIMEType);
    if( !registeredType ) // check for edge case
    {
    	if( [ext isEqualToString:@"m4v"] )
    		mimeType = @"video/x-m4v";
    	else if( [ext isEqualToString:@"m4p"] )
    		mimeType = @"audio/x-m4p";
    	// handle anything else here that you know is not registered
    } else {
    	mimeType = NSMakeCollectable(registeredType);
    }

    CFRelease(UTI);
    return mimeType;
}

-(NSString *)mimeTypeForFileAtPath:(NSString *)path error:(NSError **)err {
  NSString *uti, *mimeType = nil;

  if (!(uti = [[NSWorkspace sharedWorkspace] typeOfFile:path error:err]))
    return nil;
  if (err)
    *err = nil;

  if ((mimeType = (NSString *)UTTypeCopyPreferredTagWithClass((CFStringRef)uti, kUTTagClassMIMEType)))
    mimeType = NSMakeCollectable(mimeType);

  return mimeType;
}