According to an old blog entry from Aaron Giles, the value for the -prescale parameter is an integer from 1 to 8.
But in practice, I think the maximum is limited by the resolution of your monitor.
For example street fighter has a resolution of 384 × 224.
Assuming a typical monitor with 1920 x 1080 resolution...
If you set prescale 1, the screen is rendered at 384×224 before scaling up to your monitor resolution and...
prescale 2 = 768 x 448 before scaling up
prescale 3 = 1152 x 672 before scaling up
prescale 4 = 1536 x 896 before scaling up
prescale 5 = 1920 x 1120 before scaling up
Note that the vertical at prescale 5 is taller than the monitor's native resolution...
1120 > 1080
So I believe that the highest prescale that would work for Street Fighter and a 1920 x 1080 monitor is prescale 4.
Controls the size of the screen images when they are passed off to the graphics system for scaling. At the minimum setting of 1, the screen is rendered at its original resolution before being scaled. At higher settings, the screen is expanded by a factor of before being scaled. With -video d3d, this produces a less blurry image at the expense of some speed. The default is 1.
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