All brass instruments without valves are limited to four notes. Think of taps. 1-1-2, 1-2-3, 1-2-3, 1-2-3, 2-3-4, 3-2-1, 1-2-3.
Depending on your chops, you can take it up or down an octave or two, but they are still the same four notes. And, if you are skilled, you can slide a little, as illustrated with the "going home" fox horn video.
But, there is no way to play the bugle as was done in "Here to Eternity."
Now we can introduce valves. Same principle, but the valves lengthen or shorten the distance the sound travels, so you can get the notes between the four.
That sounds complicated, doesn't it? Bugle notes as base. Reroute it through a longer or shorter tube. Voila, it is a different sound than a straight bugle can make.
But it remains that this is where a bugle stops and valved brass instruments started -- you can get all the sounds because your are essentially playing several bugles at once.