I want to convert a 30fps MP4 file i recorded of a Heron hunting gophers

into a slow motion version, i realize i could maybe edit the file header and change the frame playback rate

but i would rather just multiply/duplicate the frames triple or more, so it played at 30 FPS but moved at 10 or less

its only 48 seconds long, but i would like to show the Heron's hunting strike and movements in slow motion

this way i can upload and anybody that plays it will be able to see the strike in detail

what is the best program to accomplish this, vdub ? or something else

its been a few years since i did anything like this

thanks