How to save base64 video to regular video (mp4)?

Question

Character encoding

Hey!
The video is loaded in base64 format.
There is a task of its storyboard. Didn't find a way to do this with base64 format. That is, you need to save it as a regular video, and then use ffmgeg to make a storyboard. But I can't find a way to save it. For photos, this is solved using file_put_contents, but it does not work for videos. Can you help?