How to stretch full screen rca PSP and dreamcast? raspberry pi3 and how to emulate on better resolution?

[edneyhelene]

Hello there, i setted up overscan and 4:3 as my tv is tube and im using rca cable!
I would love to stretch the image the same way i do usually do on pc...

setting sdtv_aspect=1 stretchs it but psp and dreamcast emu seems to continue with black bars, how do i stretch them? i have overlay and i do prefer stretched also i do use nice filters that makes it great!

Other question is how do i change the emulator resolution to make the image better?