Hi fuanevich40,
motion blur just render past frames with less opacity. If there is no difference between past and current pngs (position, stretch, deformation or whatever you can do with a png inside Synfig Studio) you don’t see any difference. Same would happen if you create some layers and don’t move them at all. Motion blur wont produce any visible effect apart of slow down the render time.
-G
The problem was… humm… I… well… I just didn’t notice that ‘Moution Blur Layer’ must be under a .png layer. I misunderstood the encapsulation feature… Now everything is perfect! Thanks you, Synfig developers!