2D Tracking - Nuke 101: Professional Compositing and Visual Effects - page 237

The red-green image you see is a color representation of the movement the
CornerPin node is creating. These are the motion vectors mentioned earlier.
5. Switch back to viewing the RGBA channel set.
To actually have motion blur, you need to use a filter node called VectorBlur.
VectorBlurknowshowtotakemotionvectorimages,liketheonescreatedbyMo-
tionBlur2D or rendered out of 3D applications, and turn them into motion blur.
6. Attach a VectorBlur node from the Filter toolbox after MotionBlur2D1.
7. Set the UV Channels property for VectorBlur1 to Motion.
Because you created the motion vector data in the motion channel set, you are
calling for it here as well.
8. IncreasetheMultiplypropertytoavalueof100orso,justtoseehowthedirection
of blur matches the direction of motion. View Merge1 ( FIGURE 5.35 ) .
Figure 5.35. The VectorBlur node blurs in the direction of the motion.