The acoustic version of Gotta Be You on A Year In The Making. Near the end, they 
sing this with Niall playing guitar. This is it: 

No capo

Intro: 
G  Cadd9  G  D

       G
Girl I see it in your eyes you're disappointed
Cadd9
Cause I'm the foolish one that you anointed
G                  D
With your heart, I tore it apart
                G
And girl what a mess I made upon your innocence
Cadd9
And no woman in the world deserves this
    G                        D
But here I am asking you for one more chance

        G             Cadd9
I'll be here by your side
          G             D
No more fears no more crying
           G            Cadd9
But if you walk away I know I'll fade
               G          D
Cause there is nobody else

              G  Cadd9  G  Cadd9
It's gotta be you, only you
              G  Cadd9  G  Cadd9
It's gotta be you, only you
     G  Cadd9
Only you

Outro: 
E|-----2-|
B|---3---|
G|-2-----|
D|-------|
A|-------|
E|-------|

D  G  D  G




They only play that much in the documentary, but to play the whole song the chords are this: 

For the intro, verses, pre-chorus and bridge: 
G  Cadd9  G  D
For the chorus: 
G  Cadd9  G  Cadd9
For the outro: 
D  G  D  G