Would it need a buffer?
I don’t understand fully how the OSSC works but what I do understand is the OSSC gets the line from the analogue signal and then pumps it out digitally either doubling, tripling etc the output line.
Is it possible, to say, when it reaches line 960, it then outputs 120 blank lines? It won’t use the full screen size of 1080 and will ultimately cause it to be in a box in the middle of the screen, but it will make the resolution more standard and accepted by more TVs.
I have seen an option which asks which resolution you want one of the multipliers to output.