Thank you, thank you!
That's my video you just posted!
I posted it to youtube because someone on here was having issues with casting on in the middle of a row (saartje booties).
Longtail cast on in the middle of a row is possible, even though a bit hard to understand at first.
This video should make it clear.
I used a darker strand to show the difference between the two strands, you would use the same color.