@alphatoanant Thank you!

It looks I’m on Batocera 39 indeed. Isn’t it easier to update to 40? Or do you recommend knulli for another reason?

Update: ah, I read that 40 will be the last version so it makes sense to switch to Knulli. Thanks for the tip.

@spaceblaze Just to confirm the above code change does work.

I reexported all the videos at 480p and now have control over the size.

As it turns out, the end result is not that great a user experience so I'm reworking the layout a bit.

Will post a video once I'm happy with it.

@Simrose In my personal experience, using and configuring multiple controllers in retropie involves going into the system file and changing the cfg file every time you want to change the controller (if you have custom mapping keys as I always use like volume). Also installing new systems, you have to enter to the repo and download different packages or drivers. With Batocera you place the bios files, roms and you are running, also you have a built in file browser inside the system, even if you want to configure any emulator setting you can do it right from the main menu without using a keyboard or entering any game. This is great to apply global settings like resolution, shaders or bezels.
For me its better and has much more options but Retropie has a better forum and support for solutions. This is my experience after years of using both.