How to get the relative travel distance without distance information and Ground Truth

[ghost]

We know that due to the scale indefiniteness problem, we cannot estimate the distance traveled by the camera without distance information. However, we would like to get the relative travel distance. Can you determine the relative travel distance of the monocular camera under the following conditions?

・Input is video image (or acceleration and gyro sensor values) ・No ground-truth ・No distance information