Good night, I do not know react-native, but what I know about storing images in the database, Daria to store them by transforming them into Base64 depends on the language method to do this ... this link teaches a method direct by the DB is worth giving an analysis: link
There are those who risk recording the address of the image, but this method I believe to be risky because there may be depending on the server blocking the directory, permission, or even come to change the directory.
On videos, it would not be recommended to save to BD because of the size of video files that are always very large and would send the DB performance away.