If your left foot is on the left side (same with right) of the middle service line you want them pointed straight. The more you move right, the more you can point left since you dont have to defend the right side as much.Should they point straight ahead, or should they point slightly outwards. It seems you could get a better push if they point slightly outwards?
Interesting videoDon't believe that it matters all that much whether the feet land pointing at the net or point somewhat outward. Not really sure if they land with a 45 degree angle (outward) unless you have taken a lot of ballet or have a natural (duck foot) turnout. By landing straight or at a moderate angle, it might be somewhat easier to push off the inside (instep side) of one foot to take a step with the other foot (after landing the split step).