Question: Where to find the Keycodes?

[mokrates]

I have a TV which responds to this kind of remote control. One button I would use, though, is the one to open the source menu (to choose hdmi1-3, AV or tuner). None of the key codes in your list seem to work, though.

Google didn't really help me (I just found another github project implementing this with a different frontend), so I try it this way:

Can you tell me where you found this codes? Is there a spec or a firmware one can get these codes out of?

Thanks