All Line Regiments of infantry have a Corps of Drums or Pipes and Drums in Scots Division. This has been in place since the 1850s when the drummers of a regiment were brought as one, under the command of a Sergeant Drummer, which changed to Drum Major in the 1920s. Before that each Company had 1 Side Drummer and 1 Fifer, both of which were classed as 'Drummer'. Since the early 1800s, all 'Drummers' of the Army had to be competent on the Bugle as well. This custom continues to this day.
That might clear up the situation in which it appears at Rorke’s Drift that there were only drummers, Calgey, Hayes, Keefe and Meehan of the 24th, but a bugler appeared on the film.
The bugler played 'Stand Too', which oddly enough sounds identical to the 1st Battalion, A&SH Regimental Call, which at that time would have been the regiment call of the 1st Battalion, 91st Highland Foot.