I think non lagged dvd-movie playback on classic ppc have the following ingredients:
OS4 with native movie player (no switching orgy with 68k cpu)
As i remembered on pc a pentium 166 can handle with some pre-buffering.
On os3.9 (Os4 too) : SCSI HDD (I try some video clips playing from ramdisk, and i think the lack of speed of the internal ide port is the main bottleneck of the story)
Software with pre buffering,
