Chewtobacca said:
I know it sounds like I'm being a pain, but I'd rather not.
That's fine. You're not being a pain.
Do `a' and `b' have the same number of frames? Are they both in the same color-space (RGB32)? Does a.info() and b.info() look more-or-less the same?
Try experimenting with two different (shorter!) sources. Are you still experiencing the same problem?