How do I convert a file to mp3 before saving django?

I found some information on extending and changing the save() method on my model, but a few other people mentioned that it was bad practice to do that, and one should instead modify the admin form.

Extracting the audio from a mp4 is easy using moviepy, I just need to run these lines:

from moviepy.editor import *

audio = VideoFileClip("test-file.mp4").audio
audio.write_audiofile("audio.mp3")

However, I do not know where to put this within my model to ensure it gets run and saves the correct file.

My model looks like this:

Class MyModel(models.Model):
    audio = models.FileField(upload_to=update_filename)

It's important this code is executed before the file gets saved, and the audio file is the one getting saved to the audio attribute of my model.

Instead of changing the save method, I needed to change the clean method, which is where the data for a model is validated and where one can modify the attributes of a model.

from django.db import models
from django.core.exceptions import ValidationError
from moviepy.editor import *

class MyModel(models.Model):
    audio = models.FileField(upload_to=lambda i, f: f[0:-4] + ".mp3")

    def clean(self):
        super().clean()
        extension = self.audio.name[len(self.audio.name) - 4:]
        file = self.audio.file
        file.__class__
        if extension != ".mp3" and extension != ".mp4":
            raise ValidationError("Incorrect File Format Uploaded. Valid Formats: (MP3, MP4)")
        elif extension == ".mp4":
            file_audio = VideoFileClip(file.temporary_file_path()).audio
            new_file_path = file.temporary_file_path()[:-4] + ".mp3"
            file_audio.write_audiofile(new_file_path)
            file.file.name = new_file_path

It's important to run super.clean() before modifying a model's attributes, because if one runs it after modifying an attribute, it will return a ValidationError.