Even if you were to avoid Amiga IDE by using CPPC SCSI, Phase5's dual CPU cards lack L2 cache, have slow RAM, and worst of all have the dreaded context switches.
Even if you were to run on OS4 or MOS to avoid all PPC/68k context switches and used a hand-optimised player and divx codec, I SERIOUSLY doubt that any CPPC, even an overclocked one, is fast enough to play the movie properly.