Recommandation for on-premises video file transcoding server accessible via REST API? I am looking for a video file transcoding solution that I can run on an on-premises server and access via a REST API.

While I found lots of commercial cloud services (e.g. https://www.filestack.com/products/audio-video-transformations/ or https://zencoder.com/en/), I could not find an on-premises video transcoding server, neither open source nor commercial.

Do you have recommendations? Do you use a custom built solution?
Telestream used to make one called FlipFactory that I have used (a long time ago). I believe it's called Vantage now. https://www.telestream.net/vantage/overview.htm
A lot of people do this kind of thing in the cloud now using things like Amazon's Elastic Transcoder 
https://aws.amazon.com/elastictranscoder/