I tried Xamarin.MP4Transcoder but on some high resolution videos it went into exception.
on some videos the compression was successful but only reduced the size by 50%.
uncompressed videos are too large to be sent to the server in an acceptable time.
I found a very interesting native library in java https://github.com/AbedElazizShe/LightCompressor
it would be interesting to know if binding in xamarin environment is possible