Meta Slider - Flex Slider - Custom Start Slide (based on URL parameter)

/**
 * INSTALLATION: this code should be pasted into your theme's functions.php file.
 *
 * Use this filter to allow linking to a specific slide (Flex Slider only)
 * Eg, http://www.yourSiteUrl.com/yourPage?startAt[563]=3&startAt[123]=2
 */
function metaslider_flex_start_slide($options, $slider_id, $settings) {

    if (isset($_GET['startAt'][$slider_id])) {
        $start_slide = intval($_GET['startAt'][$slider_id]) - 1;
        if ($start_slide > 0) {
            $options['startAt'] = $start_slide;
        }
    }

    return $options;
} 
add_filter('metaslider_flex_slider_parameters', 'metaslider_flex_start_slide', 10, 3);