Processing files in a folder using Python

I wanted a way to run the contents of a folder through ffmpeg and turn some mp4 files into avi's my dvd player could play. This program reads through a folder and, depending on file extension, passes it to another program. The code below has been extended to optimize PNG and convert JPEG's to JPEG XL files.

Python Source

#
# Process files in a folder
#
import sys
import os
import subprocess

folder=""
if len(sys.argv)==2:
    folder=sys.argv[1]
else:
    print("Processes files in a folder")
    print("Usage: "+sys.argv[0]+" [folder]")
    exit(0)
	
#
# Check folder exists
#

if os.path.isdir(folder)==False:
    print("Cannot find this folder?")
    exit(0)
	
#
# Go through files in this folder!
#

files=os.listdir(folder)

for infile in files:
    outfile=""
    infile=folder+"\\"+infile
        
    # Run the MP4 through FFMPEG (which is in my path)
    if infile.endswith(".mp4"):
        outfile=infile[:-3]+"avi"
        runme=["ffmpeg.exe","-i",infile,"-vtag","xvid","-c:v", "libxvid","-q:v","5",outfile];
        
    # Run the PNG through OPTIPNG (which is in my path)
    if infile.endswith(".png"):
        outfile="Optimising"
        runme=["optipng.exe","-preserve",infile]

    # Recompress a folder of JPEG files as JPEG XL using CJXL (which is also in my path)
    if infile.endswith(".jpg"):	
        outfile=infile[:-3]+"jxl";
        runme=["cjxl.exe",infile,outfile];
   
    if outfile!="":
        # Only convert if the destination file does not exist so we do not overwrite!
        if os.path.exists(outfile)==False:
            print(infile," => ",outfile);
            subprocess.run(runme,stdout=False,stderr=False)
        else:
            print(infile," == Skipping! (Already processed?)")

    else:
        print(infile," == Skipping! (Unknown file type)")		

Running the program

Save the above as something, folder.py for example, then run it giving the path of a folder, e.g:

#skip>py folder.py test
test\witch_transform.mp4 => test\witch_transform.avi

And if we run it again:

#skip>py folder.py test
test\witch_transform.avi == Skipping! (Unknown file type)
test\witch_transform.mp4 == Skipping! (Already processed?)

Modifying for other uses

The above can be easily modified for other tasks, for example to compress a folder of files as JPEG XL you could add the following:

    # Recompress a folder of JPEG files as JPEG XL using CJXL (which is also in my path)
    if infile.endswith(".jpg"):	
        outfile=infile[:-3]+"jxl";
        runme=["cjxl.exe",infile,outfile];

Updated 19/07/2025
Created 12/12/2024