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

Question

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.

Answer 1

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.