Filters add some effect on the output image, such as glare or blur, or overlay of some kind of image etc..
Multiple filters can be applied. They are applied in order from top to bottom.
In the above sample, glare and blur effects are applied on the output, and then Legend that shows the time information is added at last. In this case, No glare nor blur is applied to the legend. If Legend Filter is set at the top most, the text would be blurd.