The royal coronation ceremony for His Majesty King Bhumibol Adulyadej (King Rama IX) was performed in the Grand Palace on 5th May 1950, four years after he actually assumed his kingship in 1946. At the traditional coronation ceremony, His Majesty pronounced the traditional oath of accession: “We shall reign with righteousness for the benefits and happiness of the Siamese people.” The following videos are of foreign newsreels about the coronation.
If you are curious about what the coronation of King Rama X will be like on 4th May 2019, then take a look at these old newsreels of the coronation of King Rama VII and King Rama IX
Also of interest is this old newsreel of the coronation of King Prajadhipok (King Rama VII) in 1926.