SELECT 
  video_id, 
  embed, 
  thumbnail, 
  order_number 
FROM 
  cscart_product_videos 
WHERE 
  product_id = 65938 
ORDER BY 
  order_number ASC

Query time 0.00038

JSON explain

{
  "query_block": {
    "select_id": 1,
    "read_sorted_file": {
      "filesort": {
        "sort_key": "cscart_product_videos.order_number",
        "table": {
          "table_name": "cscart_product_videos",
          "access_type": "ALL",
          "rows": 26,
          "filtered": 100,
          "attached_condition": "cscart_product_videos.product_id = 65938"
        }
      }
    }
  }
}

Result