Linux

I’ve done that sorta thing before with ffmpeg; should do the trick for ya.

I do not know why this got so downvoted (maybe for cross posting too much?, if so, try to reduce that a bit). Someone has said wpaperd already, but there is also awww. As to exactly get the rate of switching.

awww img <path/to/img>  

# You can also specify outputs:  
awww img -o <outputs> <path/to/img>  

# Control how smoothly the transition will happen, as well as its frame rate.  
# --transition-step: smaller values = smoother. Default is 2 if --transition-type is `simple`, and 90 if it is not.  
# --transition-fps: Default = 30.  
awww img <path/to/img> --transition-step <1 to 255> --transition-fps <1 to 255>  

# There are also many different transition effects:  
awww img <path/to/img> --transition-type center  

# Note you may also control the above by setting up the AWWW_TRANSITION_FPS,  
# AWWW_TRANSITION_STEP, and AWWW_TRANSITION environment variables.  

# To see all options, run  
awww img --help  

ffmpeg for fade, then mpvpaper for background set