That video is OK if you have a relatively small project.
However, if you have a larger project you will need to know how to piece each border so it is long enough. I couldn't easily find a video on the web, so please excuse the wordiness below.
If you have a single border or parts of multiple borders that need to be longer that what you can cut from the fabric then you sew each individual border separately so that each one is long enough to use. I join on the diagonal as it is more pleasing to the eye and doesn’t draw the eye away from the actual quilt design. This is done by having the 2 pieces at 90 degrees from each other with some overlap extending, and then sewing from where these tails meet on the outside corner - it looks like a diagonal seam. [A picture is at: www.quiltville.com/borderhints ]
If you are using side-by-side mitered borders in your quilt, sew all of the strips for each side together lengthwise, once each strip is long enough, plus more than needed for the ends to meet and even have some extra 'tail extending on both ends of each side. Add each multi-border unit to the quilt one side at a time. Sew each border to the quilt up to 1/4" from the corner edge. Thus, if you have multiple borders you will treat the finished sewed borders as single units.
Borders are easier to match at quilt corners when you press seam allowances between the strips in side borders in the opposite direction of the seam allowances in top and bottom border units. The seam allowances will butt into each other nicely for a perfect match.
Once borders are sewn onto the quilt, turn quilt Right Side Up [facing you] on an ironing surface. Put one border edge over the other. Work with this top border to form a miter [45 degrees – you can do this by folding the top border so that the tail match with the other border’s tail] from the inside corner of the border [where it stopped ¼” from edge] to the outermost edge of the border. The top folded under border ‘tail’ should after turning be right on top of the lower most border ‘tail’. Pin tails that are visible. Press well with Best Press. Then gently pin a bit away from the pressed line on the inner side of the press to keep in alignment. Sew right on the pressing line from that ¼” seam stop to the edge making sure that the quilt body is folded out of the way. Backstitch at the end where the quilt body is. After sewing check for appearance again before trimming. Trim tails away leaving 1/4" seam allowance.
This is the easiest way to do it. If the borders aren’t perfect a ‘fudge factor ‘ can be worked into the miter and it will still look great.
Hope this helps.
ali