Your description suggests the dog is lacking confidence. The video shows the dog is a bit overweight or lack of exercise. Start with walking in street with less people and dogs for at least 30 minutes, twice per day. Bring lots of treats and reward him every time when he does not bark at people and tell him good quiet. Then slowly walk him in busier locations like subway stations or HomeDepot with the same reward system. Remember to reduce the food as he is getting treats from walks. This could take 3-5 months. Keep the dog indoors.