AudioSource.GetOutputData returns 0 every time

I am trying to log the volume of audio that is playing.

Here is my code:

 sing System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 
 public class visualiser : MonoBehaviour
 {
     public float[] samples = new float[256];
     float a;
     AudioSource source;
     // Start is called before the first frame update
     void Start()
     {
         source = GetComponent<AudioSource>();
         source.Play();
     }
 
     // Update is called once per frame
     void Update()
     {
         source.GetOutputData(samples, 0);
         foreach(float s in samples)
         {
             a += Mathf.Abs(s);
         }
         Debug.Log(a/256f);
     }

No matter what I do it always logs "0". I have tried every solution that I have found. Nothing worked. If anyone knows what is the problem please answer.