Okay, Im going to be very critical now, so if you dont like that, please look away now
Your shoulders are hunched up, meaning you are holding tension and therefore restricting the flow in your punch. It is sometimes good to 'round your shoulders', but it is obvious you are holding a huge amount of tension. This is shown in the weakness of the punch
You are hitting too low - this will put a lot of strain on your joints (because all of the force is impacting back onto your elbow as opposed to your body)
You should not hit a bag like that using a fixed stance (use a wallbag if anything). If your opponent moves, you need to move. You will end up hurting your wrists because the bag could swing back at an awkward angle. If you watch a boxer working a bag, he moves his body to the angle the bag travels at (or has a partner holding the bag for him)
Generally the video was frustrating to watch - like a bad David Blaine, unsure of what he is trying to tell the audience. My advice is to go and watch a Master Wong youtube vid, and you will see what I mean about presentation
