This Unity behaviour acts as a music playlist, crossfading and looping through an entire audio playlist

MusicPlayer.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class MusicPlayer : MonoBehaviour
{
    private AudioSource aTrack;
    private AudioSource bTrack;
    private bool aTrackIsMain;
    private float maxTrackVolume = 0.5f;

    private float lastATime;
    private float lastBTime;

    public AudioClip[] playlist;
    int playlistPos = 0;
    int rollOvers = 0;

    // Start is called before the first frame update
    void Start()
    {
        var sources = GetComponents<AudioSource>();

        aTrack = sources[0];
        bTrack = sources[1];

        aTrackIsMain = true;
        aTrack.volume = 0f;
        bTrack.volume = 0f;
        aTrack.clip = playlist[playlistPos];
        aTrack.Play();
        bTrack.clip = playlist[playlistPos];
        bTrack.Play();
    }

    int GetNextPlaylistIndex()
    {
        var value = playlistPos;

        if (playlistPos + 1 >= playlist.Length) return 0;
        else return playlistPos + 1;
    }

    // Update is called once per frame
    void Update()
    {
        if (aTrackIsMain)
        {
            aTrack.volume = Mathf.Lerp(aTrack.volume, maxTrackVolume, Time.deltaTime);
            bTrack.volume = Mathf.Lerp(bTrack.volume, 0f, Time.deltaTime);

            if (aTrack.time < lastATime)
            {
                rollOvers += 1;
            }
        }
        else
        {
            aTrack.volume = Mathf.Lerp(aTrack.volume, 0f, Time.deltaTime);
            bTrack.volume = Mathf.Lerp(bTrack.volume, maxTrackVolume, Time.deltaTime);

            if (bTrack.time < lastBTime)
            {
                rollOvers += 1;
            }
        }

        lastATime = aTrack.time;
        lastBTime = bTrack.time;

        if (rollOvers > 1) NextTrack();
    }

    void NextTrack()
    {
        rollOvers = 0;
        playlistPos = GetNextPlaylistIndex();
        aTrackIsMain = !aTrackIsMain;
        if (aTrackIsMain)
        {
            lastATime = 0f;
            aTrack.clip = playlist[playlistPos];
            aTrack.Play();
        }
        else
        {
            lastBTime = 0f;
            bTrack.clip = playlist[playlistPos];
            bTrack.Play();
        }
    }
}