Folder structure (tweak as per requirement)
/home/z/Documents/ConversionUtil/Image/image.png
/home/z/Documents/ConversionUtil/Script/Conversion.py
/home/z/Documents/ConversionUtil/Input/
/home/z/Documents/ConversionUtil/Output/ 


image.png can be any image name/format (tweak code if different)
Conversion.py

import sys, os
import os.path
 
imgfile  = "/home/z/Documents/ConversionUtil/Image/image.png"
ipfolder = "/home/z/Documents/ConversionUtil/Input/"
opfolder = "/home/z/Documents/ConversionUtil/Output/"
 
for file in os.listdir(ipfolder):
    filename = file[:file.rfind(".")]
    print "Converting file " + filename
    cmd = "ffmpeg -loop 1 -y -i {0} -i {1}{3}.mp3 -shortest {2}{3}.avi".format(imgfile, ipfolder, opfolder, filename)
    print "Ececuting command: " + cmd
    os.system(cmd)

Command to execute

python /home/z/Documents/ConversionUtil/Script/Conversion.py

On successful completion find video files in folder
/home/z/Documents/ConversionUtil/Output/

A personal technical diary… To the point… Precise