You bet, but have you *seen* it? Questions about "why can't my super-fast G4 play HD" are a dime-a-dozen on Apple forums, so if "just worked" you'd think there would be fewer questions.
One thing people forget about comparing G4s (at least the ones Apple used) to just about any other CPU of similar vintage is it has a *much slower* CPU/Memory bus, and video playing is all about bandwidth. We're not talking a little slower, we're talking laughably slower. (The 2001 vintage Athlon Thunderbird motherboard I have stuck somewhere in my junk pile has a fatter CPU-Memory pipe then even the very fastest MDD Mac thanks to it actually supporting DDR rather then SDR transfers. DDR-memory G4 Macs are still throttled to SDR at the CPU socket.)