Playing Along

What's the context here? Are they playing along with someone playing something they've never heard before or are they just playing along to a song on the radio? Can they do it for 3 - 5 tracks in a row or just one at a time

So I've noticed many amateur guitar players who are able to "play along" with someone else or a tune on the stereo etc.

I'd describe it as fills or short riffs, whatever the term is.
I've asked them about it but they say it just comes to them or they play what seems right.

This hasn't worked for me.

I'm guessing they are identifying the key and playing a scale in that key?

Your comments are all appreciated!

Thanks

More or less. Most modern pop music uses a small bunch of chords, will only modulate once (if at all) and will have a simple structure based around a multiple of four bars.

If you get the first chord right, then you know what the other chords are going to be - find the bass note, start the melody an octave above the 3rd or the 5th and the rest of the chord can only be one or two more notes. Chords I, IV and V in your key will be the most important; chord vi is the next most frequently used, and chord ii is often used as a substitute for chord IV. The solo in the middle will probably be a basic pentatonic, although don't discount Dorian or Mixolydian modal influences.

The Pop-Punk bands will use lots of "5" chords - because they don't have the skillset to use full harmonies. More advanced musicians will use chords from outside the key - U2's song Beautiful Day is in the key of A (needs a G#), but the 4th chord in is a regular G.

I have been known to put the radio on and play along. Try it, it's good for your aural skills.

What's the context here? Are they playing along with someone playing something they've never heard before or are they just playing along to a song on the radio? Can they do it for 3 - 5 tracks in a row or just one at a time

Pretty well they can do it to any song whether familiar or not