Much like audio content, you may want to incorporate the audio that comes from video content into your podcast as well. Here are some possible sources that you can use.
1. Wikimedia Commons:
You can search through videos that are contained on this website. The associated Creative Commons license is usually indicated with the file as well. You will be able to search by category. 
2. Vimeo - Vimeo is viewing destination (like YouTube) and also a video platform. You can search for videos, filtering by Creative Commons licenses:
You can filter using various CC licences here:
3. YouTube also allows for filtering for Creative Commons licensing. Go to Youtube and do a search.
Once you have completed a search, look for the filter and select Creative Commons:
This will bring up a list of videos, in theory, that are covered by CC licenses:
