The first piece is located underneath a fireball cannon, which is covering an approach a monstar needs to use to help you. First, stand at the right ladder under that cannon, then walk to the left. Rewind (slowly) and adjust the rewind to make sure the monstar can get to the platform. When it's there, quickly jump on it to reach the puzzle piece.
It is possible to exploit jump physics and get the piece.
The second piece is covered by a cannon shooter. As there's not enough time to cross, you will need to adjust the phase of the green diagonal cannon so that it intercepts some of the shots. This gives enough time to reach the piece.