I can't figure out why here in my first sentence le participe passé agrees with les violonistes, but in the second it doesn't agree with les airs. I thought it should agree in both cases, since the COD is placed before the verb. What am I not seeing?
1) Les violonistes que j'ai entendus jouer sont habiles.
2) Les airs que j'ai entendu jouer étaient mélancoliques.