How to braze properly is actually a huge subject and it is not capable to get all the required information in one online post. My framebuilding class manual chapter on brazing is over 10 pages long. Neither is it possible to give a proper evaluation from just a video but that is much better than just some pictures. Here are some basic things I noticed that include observations already made by redo 3. Your torch tip should be smaller (if it is a Victor torch size 0 or less) and you had the volume of gas turned up too much. For this application it should be just a gentle hissing sound after you have adjusted to a neutral flame. It is important that the position of your brazing rod and flame be optimal – which each is usually about 45 degrees from the work and 90 degrees from each other. Most beginners cannot kept track of the movement of both hands at the same time. Until one of them can be on autopilot, you need to position the brass so that when it melts, it doesn't require your attention to keep it at the right place in contact with the work.
It has also already been mentioned that you were not using the right flux or the right amount of flux. Don't confuse the amount needed for silver or brass because of the example of Ritchie brazing on the front derailleur (silver needs more). It is possible to have too much for brass because the extra can obscure what you are doing.
Your goal is to control the heat with your torch so that the temperature of the brass is in-between the liquid and solid state. Of course on such a small fillet that is very challenging to do and makes racks a lessor choice for a learning experience. In your case you went from melting temperature to overheating in about 1 second. Basically in this situation you control the heat by flicking the flame quickly on and off the joint.
Good brazing involves using your left and right hand independently from each other. You made a common rookie mistake (somewhere around the 3 minute mark) when your flame hand went in towards the joint at the same time your brass hand went in while the rod was melting.