I'm editing many videos, >100 with each ~45min. The editing itself is specific to each video and can not be automated. Currently I'm using freeware to do this.
What I'm missing is a way to delegate the export tasks to a batch job running at night or maybe even another machine.
Is there a program or general setup supporting batch rendering/export of multiple projects?
I would suggest you take a look at DaVinci Resolve 14 and see if it can cover what you need. It depends on what editing you need to do as there aren't much in the way of filters available in the free version of Resolve, but it has a reasonable basic NLE and supports a batch renderer.
Virtually any decent professional software offers batch render support, but many of them have costs associated with them. Resolve is the best free option I have personally used (though I have the paid studio version.)
The straight forward way to go about it is to use Adobe Premiere. It's probably the most widely used video editing software currently (read: a lot of third party plugins, massive amount of free information online). It comes with Adobe Media Encoder. You finish editing your video and add it to the encoding queue. You can export into multiple different formats at the same time as well. Once you are ready to encode, you press go and it will encode project after project.
They have a 30 day free trial if you want to try. After that it's a monthly fee of $20.
