animation with dynamic frame rate

hi

does anybody have any sample code
showing how to create an animation with a dynamic frame rate ?

say i have in directory ‘/path/to/images’ my rendered images of an animation
named from 0.png to 1000.png

how can i create the animation so that at 0.png i have frame rate say 6
and at 1000.png the frame rate say 60 ?

  • the frame rate going up steadily

thanks
sc3*2