if( !function_exists( 'marstheme_get_the_archive_title' ) ){
    function marstheme_get_the_archive_title( $title ) {
        if( is_tax( 'video_tag' ) ){
            // changes your text here.
            $title = 'Video Tag: ' . single_term_title( '', false );
        }
        return $title;
    }
    add_filter( 'get_the_archive_title' , 'marstheme_get_the_archive_title', 100, 1);
}