random select file input in ffmpeg

Please help me! I code ffmpeg add mp3 to image but i want to select random file mp3 when add to image creat video. my code:

set INPUT=E:\image
set OUTPUT=E:\video
set mp3inseart = $(shuf -n1 -e e:\music\*) 
: encode video 
for %%i in ("%INPUT%\*.jpg") DO ffmpeg -i "%%i" -i $mp3inseart -threads 0 -shortest -preset ultrafast "%output%\%%~ni.mp4"