How do I get the first frame of an in memory video using python?

Specifically, if the frontend uploads a video (e.g webm format), how do the backend get a thumbnail from this video without writing the video to disk first?

I have read all post on stack exchange about this without any luck. All the solutions are based on first writing the video to disk. E.g with moviepy using VideoFileClip(video_path). Is there really no way to open a video from buffer in memory and getting a thumbnail?