Those pictures are just fictional.
Annealing the brass involves different tools, techniques, designing... and knowledge.
Annealing means you have to heat up a piece of a metal alloy (steel, brass... almost every kind of alloy of any metal) with a specific heating ra.
When you hit the specific temperature for the type of annealing you need, you need to keep the piece of metal at that temperature for a specific time (for the type of annealing you need)... then you cool it down with a specific cooling degree (for the type of annealing you need).
You have TTT CCT curves, you have FEM softwares to calculate times and temperatures according to the shape of the piece (that's why you need to have the 3d model of the parts of the instruments... instead of only 2d drawings).
Remember that metallurgy is not a myth, it's a science.
Does that torch make something to the brass? Yes.
Is that annealing? Uhmmm... no. not at all... not what "annealing" is supposed to be according to what metallurgy says.
Would you cook a t-bone steak with a lighter? No... difficult job, impossible to get it medium-rare. MacGyver would be able to do that, but only on emergency and high risk situation. And I really doubt he could make it medium-rare.
Those pictures are just fictional, just for advertisement...
If it was an attempt of annealing with a welding torch... you'll see all the keywork falling down (the keywork is attached to body via soldering, brazed with tin... check out the welding temperature of the tin and the range of temperatures to anneal the a copper alloy): https://i0.wp.com/www.lupifaro.com/w...03/foto-01.jpg
Sincererly, if I have to handle and work a welding torch (or an arc welder)... I'll wear safety clothing for the job, not casual stuff.
Conclusion: if the horns play good, it's not because of what they are trying to do in the pictures.
They sound good and that's it! That's what matters!