TDarr
NOTE: i don't use TDarr anymore, this page might get outdated over time.
TDarr is a service that can monitor your media collection and perform video conversion automatically for you. It's pretty complex and has an intricate plugin system to achieve the goals you prefer.
Disclaimer: i tested it, but found too complex for my needs (and limited knowledge of the matter at hand) so i don't use it nowadays.
Installation
As usual, let's create an user for tdarr, with media as main group, so it can access all your media collection:
useradd -d /data/daemons/tdarr -m tdarr -g media
su - tdarr wget https://f000.backblazeb2.com/file/tdarrs/versions/2.17.01/linux_x64/Tdarr_Updater.zip unzip Tdarr_Updater.zip ./Tdarr_Updater ./Tdarr_Server/Tdarr_Server& ./Tdarr_Node/Tdarr_Node
Now browser to http://localhost:8265/ and start having fun.
I never got to the point to use it full time, so i never bothered setting it behind the Reverse Proxy. Anyway if you want to, this page could be of help.
Also, you will need to automate the startup and running on boot, again it's very similar to all the other services, so i let you dig on that.