I started boxing late, keep at it and never let anyone discourage you. It seems like your posture gets of balance. When throwing combos, you seem to lean forward. Try to stay balanced at all times. Head between your knees. Your combos will be faster and your transition from offense to defense will be smoother. Your lead arm. Notice the elbow flare while you are jabbing? This is a telegraph to your opponent. Try to keep that elbow down and close to your ribs. Never back up in a straight line. You jump in, throw a combo, then you step straight back. When you are done with your combo, try a side step or pivot. Ingrain this and make it a habit you do without thinking about it. Hand speed looks good. Try to change level with straight shots more. Keep it up!
I also noticed on the dummy your elbows where a tad high and arms out. The arms should ride your ribs. A good rough gauge of where your arms are is thumb touching the cheek bone out of danger. Thumb touching brow/temple in danger. If you first apply keeping your elbows/arms close to your ribs, the placement will handle itself. Your elbows will slightly come up in the second position, but then you will be "crunching" your body to absorb shots and "get small" to compensate. Not to mention being attached to the floor not the ceiling to simulate movement, the dummy seems a bit "gimmicky" (especially without arms) and it probably won't weigh nearly enough once your technique reaches a good level. You seem to be putting in the work to get it there too so... soon the dummy will be retired. :good