I use a lot of playback tracks to practise and work on drum scores. And I am far from being an expert of audacity.
The playback tracks are often coming from you-tube video or live recordings.
It is very useful from an efficiency standpoint to have a lead-in count (for the tempo) added on top of the track.
For that purpose audacity offers the capability to generate a metronome track (generate > tempo track , I guess, on the English version). Very simple.
The process is as follows :
A) identify the track tempo (good old “tap and count” method or any alternate way to that…)
B) zoom on the beginning of the track and measure the time offset of the first beat with respect to the beginning of the track. Assume (eg) that the 1st beat occurs 5,25s after the beginning of the track
From that point, assuming (eg again) the tempo is 120bpm in 4/4 (ie one bar lasts 2 seconds)
let’s assume (again, sorry) that I need two bars of lead-in count : this is a total of amount of time of 4s
So the metronome track shall start 4s before the first music beat, that is to say 5,25-4 = 1,25s after the beginning of the music track.
Then one just need to invoke the “generate tempo track” command, specifying the number of needed bars, the tempo, and the offset (=1,25s) of the first tempo beat.
If the music starts immediately or very soon after the beginning of the track, you may choose to add a few seconds of blank track ahead, so that you can comfortably install your counting bars
Very simple, and convenient