virtualbox.org

When i'm installing an OS the resolution is minimal.

I'm want to record a tutorial.

Is het posible to set the resolution to 1280x720 on boot/install?

Not a software usage question, it's a guest OS configuration matter, hence moving this topic from "Using VirtualBox" to "Linux Guests" (on the assumption that this is related to your recent posts on LibreElec).

Change the guest display resolution in the normal way provided by that guest OS. Install the Guest Additions for better performance.

Assuming this is really about a Linux guest you would add the proper vga=" " tag in the kernel line at boot to force the proper framebuffer. Ask the OS distro how they want you to achieve this.