Stock footage videos are created by stringing together video clips that have already been shot. You can use this footage by paying a royalty to the image bank that has the rights to the clips you would like to use. The script for your stock footage video needs to be determined in advance and then clips that fit the story need to be identified. You can buy clips from multiple image banks as well. It may not always be possible to get exactly the clip you have in mind. In this case, you will need to modify your story and find an alternative.
Here's an example 
Companies may not have budgets for live action videos and animated videos may not be appropriate for the content they need to disseminate. In such cases, stock footage videos are a great option. Stock footage videos can be used to create awareness videos, explainer videos or even to educate and train. Stock footage can also be used in case you have a video with too many ‘talking heads’. In this case, you can cut away to stock footage to visually show what the talking head is referring to.
Stock footage videos save you time and money. If you need a video in a short span of time, then stock footage is a great option as you don’t need to shoot or edit. Also, if your story has multiple scenes, locations and character, it is likely to be expensive to shoot and you may not have the budgets. Again, you can look to use stock footage to tell your story. You could also think about using supers, animated overlays and section breakers to make your stock footage video memorable.
