When you use this kind of library, you don't have much of a choice on app size. One thing you can do is release aab instead of apk on google play.
For example, if you analyze the apk you might see, you have different .so file for different architectures.
With aab file, google can choose the right architecture to build apk for right device.
I would not worry too much about size for this kind of app, because it needs those .so files to work properly.
Another bold approach you can take is to make your own version of ffmpeg lite by removing anything that you don't need.
But that requires a deep understanding of the ffmpeg library.