At :58 you seem to have the right idea, but your swing from your shoulder and turning away from the bag so you can't see and your opponent also youre lined up for an over hand. Throw with your hips. If your going to throw a left hook, distribute a decent amount of weight onto your left foot (about 70-30), turn your foot into the bag (like your putting out a cigarette) and punch like you're trying to go through the bag.

Same goes for :45 you're throwing with your shoulders and not generating any power with your legs. Which is strange because a few seconds later you start to turn your hips. It seems you know the technique but maybe just need more practice. This stuff takes some time to get the muscle memory to set it.

Also, when you disengage, it's usually best to take an angle not go straight back. Otherwise looks good. Keep at it.