In the effect controls panel, ensure "Compute Motion Vectors" is set to Auto. For complex footage, manually set it to Accurate (Slower) .
If you have a bright light streak passing through a dark room, standard motion blur will create a dark "ghost" trail. Enable Limit by Luminance and set the threshold to 90%. The plug-in will only blur the bright pixels, preserving dark contrast. revisionfx reelsmart motion blur pro 621 plug
For compositors using Nuke or Fusion: RSMB Pro allows you to render a separate vector pass (two channels: X and Y movement). You can then reuse that single vector pass to apply different qualities of motion blur later without re-analyzing the source footage. In the effect controls panel, ensure "Compute Motion