Thailand is one of a few monarchies (like Denmark and Sweden) that have a separate anthem for the royal family, as opposed to the national anthem for the citizens. The Thai royal anthem is performed during state occasions and public meetings, as well as when a high-ranking member of the royal family is present for a function. It is also played on television and radio stations at midnight.
The royal anthem also served as the third national anthem of Siam (as Thailand was then known) until the 1932 coup. The music was composed by Russian composer Pyotr Shchurovsky[1] [2]. The lyrics were written by Prince Narisara Nuvadtivongs, the brother of the king, and were revised by King Rama VI in 1913 and officially adopted as the royal (and national) anthem at that time.
Sources:
[1] นิติการุณย์ มิ่งรุจิราลัย (Nitikarn Mingruchiralai), “ผู้ประพันธ์เพลงสรรเสริญพระบารมี,” ไทยรัฐ (Thairath), accessed February 25, 2023, https://www.thairath.co.th/newspaper/columns/996485 .
[2] สุกรี เจริญสุข (Sukree Charoensuk), “อาศรม มิวสิก เส้นทางเพลงสรรเสริญพระบารมี,” มติชนออนไลน์ (Matichon Online), July 16, 2017, https://www.matichon.co.th/news-monitor/news_602826 .
Special thanks to: Artakorn Jarusriwanna for providing me with the sheet music and Yevgeni Gorshenin for some of this information.