Looking at the plugin code on git you can see the entry: "optic_flow = 1;" Do you think that means it use optical_flow?
Unfortunately NO. I think the programmer who made the last "Speed PerCent plugin" only improved the GUI of the "ReframeRT" plugin (see the texts in the header on "speed_pc.C" by git): ================================= Derivative by ReframeRT plugin for a more easy use. It uses percentage value of the speed referred to originl speed (=100%). Some old ReframeRT parameters (Stretch and denom) have not been deleted, for future development, if any. Stretch and denom variables are set to a constant value: Stretch= 1; denom= 100.00. Speed_MIN= 1.00%; Speed_MAX= 1000.00% ================================= So, "Speed PerCent" plugin uses the original code of the "ReframeRT" plugin. Maybe the developer who wrote ReframeRT, time ago, wanted to implement OpticFlow but then gave up for is own reasons. I see that "Interpolate video" plugin uses OpticFlow and may be the developer wanted to use it on "ReframeRT" plugin. I don't know. It's a pity. IgorBeg