Audio Crossfade - OpenProcessing

mySketch
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/**
 * Demonstrates cross-fading between two audio tracks.
 *
 * The sound files are licensed from [Free Music Archive](https://www.freemusicarchive.org/)
 * Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) license.
 * - Points of no Return (ID 1285) by Lobo Loco
 * - Country Boy - Instrumental (ID 1348) by Lobo Loco
 */
​
let track1, track2;
let env1, env2;
​
function preload() {
  track1 = loadSound("country_boy.m4a");
  track2 = loadSound("points_of_no_return.m4a");
}
​
function setup() {
  createCanvas(windowWidth, windowHeight);
​
  // 5 seconds to fade in (attack), 3 seconds to fade out (release)
  env1 = new p5.Envelope(5, 1, 0, 1, 3, 0);
  env1.setInput(track1);
  
  env2 = new p5.Envelope(5, 1, 0, 1, 3, 0);
  env2.setInput(track2);
}
​
function draw() {
  background(200);
  textAlign(CENTER, CENTER)
  noStroke();
  textSize(20);
​
  let isPlaying1 = track1.isPlaying() && env1.wasTriggered;
  fill(isPlaying1 ? 'green' : 0);
  rect(0, 0, width / 2, height)
  fill(200);
  text(`Click to ${isPlaying1 ? "Stop" : "Play"} track #1`, width / 4, 50);
​
  let isPlaying2 = track2.isPlaying() && env2.wasTriggered;
  fill(isPlaying2 ? 'green' : 0);
  rect(width / 2, 0, width / 2, height)
  fill(200);
  text(`Click to ${isPlaying2 ? "Stop" : "Play"} track #2`, width * 3 / 4, 50);
}
​
function mousePressed() {
  if (mouseX < width / 2) {
    if (track1.isPlaying() && env1.wasTriggered) {
      env1.triggerRelease();
    } else {
      track1.play();
      env1.triggerAttack();
      if (track2.isPlaying()) {
        env2.triggerRelease();
      }
    }
  } else {
    if (track2.isPlaying() && env2.wasTriggered) {
      env2.triggerRelease();
    } else {
      track2.play();
      env2.triggerAttack();
      if (track1.isPlaying()) {
        env1.triggerRelease();
      }
    }
  }
}
​