Mobile libraries for recording / transcoding audio and video

Hi, we are looking for mobile libraries that allow recording and transcoding audio / video directly on the device.

Our target use case is similar to WhatsApp's recording features:
a) the user shall be able to record voice and/or video
b) the result shall be compressed, using a codec that works on both iOS and Android (e.g. mp3 for audio, mp4 for video)
c) we want to upload the resulting file to a server (we will care for this)
d) from there, audio and video files can be downloaded in Unity and played back in a web-view (this part is already implemented)

We need support for a) and b), in particular.

Most of the existing Unity packages are for playback only. There is a FMOD integration, but the FMOD license is pretty expensive. We've also seen FFmpeg Bind, but according to the comments in the Asset Store, it is not maintained anymore and won't work on Android 64bit or iOS 13+. The only option we see so far is integrating FFmpeg ourselves, e.g. by using the FFmpeg mobile.

Does anybody know of another solution / package / library? Thanks.