How to automatically upload a file on update?

Question

Django

I have a track model

class Track(models.Model):
    prepopulated_fields = {'slug': ('title',)}
    musician = models.ForeignKey(User, on_delete=models.CASCADE)
    title = models.CharField(max_length=150)
    description = models.TextField(null=True, blank=True)
    track = models.FileField(upload_to="music")
    image = models.ImageField(upload_to="tracks/", null=True, blank=True)
    slug = models.SlugField(max_length=150)
    genre = models.ForeignKey(Genre, on_delete=models.SET_NULL, null=True, blank=True)
    album = models.ForeignKey(Album, on_delete=models.SET_NULL, related_name="tracks", null=True, blank=True)

    def __str__(self):
        return self.title

Serializer for this model

class TrackSerializer(serializers.ModelSerializer):
    musician = serializers.CharField(read_only=True)
    album = UserFilteredPrimaryKeyRelatedField(queryset=Album.objects)

    class Meta:
        model = Track
        fields = '__all__'

And a view to process

class TrackViewSet(viewsets.ModelViewSet):
    queryset = Track.objects.all()
    serializer_class = TrackSerializer
    permission_classes = (IsOwnerOrReadOnly, permissions.IsAuthenticatedOrReadOnly)

    def perform_create(self, serializer):
        serializer.save(musician=self.request.user)

Text fields are substituted automatically, but how to make the picture and the track itself loaded too?