There are multiple sources of stock video of people and crowds. Many are extremely expensive you could end up paying over $30 for a single clip. There are other sources for videos of crowds, people, cities, etc. Some sources charge far less and update their content on a regular basis giving you fresh content to use in your marketing videos.
Get videos that are in HQ 4k definition that will stun your viewers, this can be done at the following link.
At the following link you can gain access to high quality royalty free stock video footage of crowds and people in various situations and locations around the world.