How to Extract Audio from an MP4 Video and Save as MP3 Using MoviePy

If you're a developer or just someone who frequently works with multimedia files, there might come a time when you need to extract the audio from a video file. For example, converting an MP4 file into an MP3 format can be useful for podcasting, audio processing, or even just separating the audio from a music video.

In this tutorial, we'll walk through a simple Python script that extracts the audio from an MP4 video file and saves it as an MP3. We'll use the MoviePy library, a powerful tool for video editing in Python.

Prerequisites

To get started, you'll need Python installed on your system along with the following dependencies:

MoviePy: A library for video editing and processing in Python.
Install it via pip if you haven't already:

pip install moviepy

The Code

Here is the Python code that does the magic:

from moviepy.editor import VideoFileClip
import os

# Input and Output paths (specific file)
input_file = "inp_mp4/my_input_file.mp4"  # Replace with the specific video file name
output_folder = "out_mp3"

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

# Check if the input file exists
if os.path.exists(input_file) and input_file.endswith(".mp4"):
    try:
        # Extract the filename without extension
        filename = os.path.basename(input_file)
        output_file = os.path.join(output_folder, f"{os.path.splitext(filename)[0]}.mp3")

        # Load video file
        video_clip = VideoFileClip(input_file)

        # Extract audio from video
        audio_clip = video_clip.audio

        # Write audio to mp3 with 320kbps quality
        audio_clip.write_audiofile(output_file, codec='mp3', bitrate='320k')

        # Close the audio and video clips to free resources
        audio_clip.close()
        video_clip.close()

        print(f"Successfully extracted audio from {filename} to {output_file}")

    except Exception as e:
        print(f"Error processing {input_file}: {e}")
else:
    print(f"The file {input_file} does not exist or is not a valid MP4 file.")

Explanation

Let's break down how this script works.

Input File and Output Folder:

The script starts by defining the input video file (input_file) and output folder (output_folder). You need to replace the "inp_mp4/my_input_file.mp4" path with the path to your actual MP4 file.

Ensure Output Folder Exists:

The script checks if the output folder exists and creates it if it doesn’t (os.makedirs(output_folder)).

Check if the Input File Exists and is Valid:

It then checks whether the input file exists and whether it's an MP4 file. If it’s not, the script will inform you and stop.

Extract Audio from Video:

The video is loaded using VideoFileClip(input_file). MoviePy automatically extracts the audio from the video file (video_clip.audio).

Saving Audio as MP3:

The audio is saved to the output folder in MP3 format using the write_audiofile() method. We specify the codec as 'mp3' and set the bitrate to 320 kbps, which is considered high-quality audio.

Clean Up:

Finally, the audio and video clips are closed using the close() method to free up system resources.

Error Handling:

If something goes wrong (e.g., the input file is corrupt or the format is wrong), the script will print an error message.

Customizing the Script

You can easily customize this script based on your needs:

Change Input and Output Paths: Adjust the file paths for your input video and output folder.

Bitrate Adjustment: You can change the audio bitrate to lower values (e.g., 128k or 192k) if you prefer smaller file sizes.
Different Formats: If you need to extract to other audio formats, like .wav or .aac, simply adjust the codec in the write_audiofile() method.

Conclusion

With just a few lines of code and the power of MoviePy, you can quickly extract audio from MP4 video files and save it as MP3. This script can be used for a variety of multimedia processing tasks, from creating podcasts to editing audio for videos. Whether you're working on a larger video editing project or just need to grab the sound from a music video, this method is efficient and easy to implement.

Final Thoughts

MoviePy is an incredibly flexible library that can handle many types of video and audio processing tasks. It allows you to do everything from simple tasks like audio extraction to complex video transformations.