So I was just watching some sm64 speedrun videos and I asked this question, "How do they setup a handcam without using a camera?" Thanks again

what

Can you tell us which videos you were watching so we can better understand what you're asking about?

I'm assuming @Darkv is asking about input displays. This depends on what platform you are playing on.

If playing on emulator, you can easily setup an input display with third party software. This thread may be helpful: https://www.speedrun.com/sm64/thread/hv4vt

If playing on console, you'd need an external, physical device (such as an arduino) that reads the inputs from the console and sends them to the PC. Then you'd use third party software (NintendoSpy is popular) to display the inputs.

Thanks SaySuprise