So the music just keeps on changing time signatures back and forth, every two bars?
no
what you're hearing is 3/4 (or, to be more precise, 6/8) figures in 4/4. the first four "beats" are actually dotted quarter notes (or quarter notes tied to 8th notes, or other ways of grouping 1.5 beats). the last two in the phrase are quarter notes.
1.5 + 1.5 + 1.5 + 1.5 + 1 +1 = 8
so it would be written as 2 bars of 4/4
Sonic Cannon posted...
2 bars of 6/8 followed by 1 bar of 4/8.
I think it's more likely just 3/4 and 4/4 though. Only some of the instruments are playing triplets.