Hi Matt,
There are a couple of reasons why this is not possible.
1) We’ve received numerous reports of poor performance using SATA cards in G4s. The 33MHz PCI slot on the G4 will not be fast enough to provide decent performance for the playback of uncompressed HD.
2) When you add a DeckLink card, you place an even heavier load on the shared PCI bus in the G4. You’ll simply run out of bandwidth to do any uncompressed HD work. This is why the G5 and the new PCIe G5s are much better for uncompressed HD work.
3) Playing uncompressed HD and doing down conversion is a fairly hefty job. The G4 does not have the grunt to do this.
regards
Kristian Lam
Blackmagic Design