How to select by multi part index in tarantool?

Question

NoSQL

Actually there is an index

box.space.posts:create_index('category_listing', {
    type = 'tree',
    parts = { 8, 'integer', 12, 'string' } ,
    unique = false,
    if_not_exists = true
});

8 field is a timestamp
12 - post type
The problem occurs when trying to specify an iterator

box.space.posts.index.category_listing:select({ 1486499758, 'videos' } , {
        iterator = box.index.GT,
        limit = limit,
        offset = offset
})

You must select articles from the 'videos' category where the timestamp is greater than the specified date