500p for anyone who can help me figure out the name of this old animated film?

[HydroPonics]

i barely remember it, but it was like 70's era animation i think.

the only scene i can remember clearly is an American soldier, during World War 2,
comes upon a piano inside the rubble of a building that had been blown up. he starts playing a melody when a German soldier comes in pointing a sub machine gun. the allied soldier appears to notice hes been discovered, but keeps playing as if he isnt in any real danger, his skills with the piano start to mezmerize the german and the german gets in a trance with the music for a brief moment.... until finally snapping out of it and unloading his clip into the allied soldier playing the piano, killing him.

someones gotta know...