On my A4000T with 060 and 233, CVisionPPC, Delfina Lite and a 120GB IDE Seagate harddisk converted to SCSI3, I used Frogger.WOS and could watch divx movies without any frame skipping while Defina decoded the audio with a custom overlay screen resolution.
Frogger is ppc, ffplay is 68k. Ffplay doesn't do overlay (at least until the particular amiga sdl does it). You could not play those same videos with ffplay, even if the audio would use delfina.
I wonder though: why ffplay? Last I checked mplayer was much faster.