Instructions for working the Tubular Cast-On (demonstrated in the video above):

Using scrap yarn and the Backwards Loop Cast-On, cast-on half the number of total stitches you want. Break yarn.
Using your main yarn:
Row 1: *K1, YO*, repeat between *s across all stitches. (If you have an odd number of stitches, end with K1.)
Row 2: *with yarn in front, slip 1 purlwise; K1*, repeat between *s across all stitches.
Row 3: *K1; with yarn in front, slip 1 purlwise*, repeat between *s across all stitches.
Repeat Rows 2 and 3 once more.
Pick out scrap yarn.