Automating Image Conversion with Python: An Introduction to the AVIF Format

This post introduces a Python script that automates the conversion of images into the AVIF format.

What is the AVIF Format?

AVIF is a modern image format based on the AV1 video codec.
It offers:

• very high compression rates
• excellent image quality even at low bitrates
• smaller file sizes compared to JPEG or PNG

Particularly for websites, AVIF is interesting because it reduces loading times and bandwidth usage without visible quality loss.

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Overview of the Script

The following Python script uses the standard libraries os and subprocess to:

1. Find images in a source folder
2. Convert them to the AVIF format using FFmpeg
3. Output the file size savings per file

It supports PNG, JPG, and JPEG files by default.

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Python Script for AVIF Conversion

import os
import subprocess

def convert_to_avif(source_folder, output_folder):
    # Ensure the output folder exists
    if not os.path.exists(output_folder):
        os.makedirs(output_folder)

    total_files = 0
    converted_files = 0

    # Iterate through all files in the source directory
    for filename in os.listdir(source_folder):
        if filename.lower().endswith(('.png', '.jpg', '.jpeg')):
            total_files += 1

            source_file = os.path.join(source_folder, filename)
            output_file = os.path.join(
                output_folder,
                os.path.splitext(filename)[0] + '.avif'
            )

            original_size = os.path.getsize(source_file)

            command = [
                'ffmpeg',
                '-i', source_file,
                '-c:v', 'libaom-av1',
                '-crf', '30',
                '-preset', 'slow',
                output_file
            ]

            try:
                subprocess.run(
                    command,
                    check=True,
                    stdout=subprocess.PIPE,
                    stderr=subprocess.PIPE
                )
                converted_files += 1

                new_size = os.path.getsize(output_file)
                reduction_percent = 100 * (1 - (new_size / original_size))

                print(f"{filename}: reduced by {reduction_percent:.2f}%.")

            except subprocess.CalledProcessError as e:
                print(f"Error converting: {source_file} – {e}")

    print(
        f"Conversion completed. "
        f"{converted_files} of {total_files} files were converted."
    )

# Adjust paths
source_folder = ""
output_folder = ""

convert_to_avif(source_folder, output_folder)

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Notes Before Running

• Adjust the source and target folders in the script
• Make sure FFmpeg is installed
• FFmpeg can be downloaded from the official website if needed

After running, all supported images will be converted automatically and the respective size reduction will be printed.