Replays for non-Zero-K owners

You can manually download the .demo from the replays page without Zero-K installed, but then you need to manually ensure you have the correct engine/map/game version.

So you can't actually watch the replay without the game installed. This is the same with all spring games.

replays are, as the name suggests, the recorded sum of all commands/actions given by all participating players/spec. so, to replay, your spring engine ist started with the zero-k definitions of everything and at each given time each command ist executed. units move, fire, etc as if the game is played at that exact moment. so i have no clue what you mean with mp4, because camera position etc is not set...

in short, you can make potentially infinite videos [mp4, mkv, etc..] with a single replay [.demo]

so you can not have a direct conversion between the 2

the best you can do is to run the game then record what you want.

IFAIK all other games which use replay system require the game to run the whole replay. no other way around it. if you want the video, you have to record it yourself.

I am probably remembering it incorrectly, but I think PepeAmpere once made some dotwars preview.

I wonder if it would be possible to automate creating previews.

Hardly easy, especially if you want good results. You're welcome to write an example

You have replays locally. Demonstrate you can do it on your own machine on a few examples, and from that we can try building a more general solution.