This animation looks fine:
It is however interlaced footage (jagged edges!), so there are a couple of things that might be going wrong:
– you have the wrong field order (that would cause jittery motion, not true blockyness)
– you’re outputting only 1 field to beta.
Solution to the first is simple. change your output settings to render in the correct fieldorder
The second one:
I don’t know how exactly you’re getting it out of the Blackmagic,
But after effects usually throws away one field for displaying on the computer monitor.
Most NLE’s like Final Cut Pro do the same on screen, and sometimes also to the realtime monitor (depending on what quality you’re working in)
In effect these de-interlacing options are reducing the vertical resolution in half, so there come the blocks.
So the problem is in how you’re outputting to tape.