Spotify uses a combination of event tracking, background processes, and real-time triggers to detect if you've been listening for 30 minutes and then push an ad. Here's exactly how it works:

✅ 1. Session Tracking (Listening Time)

• As soon as you press play on any song, Spotify starts a listening session in the backend.
• The session keeps track of:
  • When you started the song.
  • When you paused or skipped the song.
  • Cumulative listening time.

👉 This data is sent to the backend server in real-time.

✅ 2. Heartbeat Pings to Backend

• Spotify continuously sends "heartbeat" pings to the server every few seconds to track:
  • Is the user still listening?
  • Is the app in the background/foreground?
  • Has the user paused the song?
• These pings look like:

{
  "userId": "12345",
  "songId": "abc123",
  "timestamp": "2025-03-10T14:00:00Z",
  "isPlaying": true,
  "device": "Android",
  "sessionDuration": 1730
}

👉 Session Duration keeps increasing as long as the user is listening.

✅ 3. Cumulative Listening Time Tracking

• Spotify doesn’t count paused time or skipped time.
• It only counts the time when audio was actively playing.
• For example:
  • If you listen for 15 minutes, then pause for 10 minutes, and resume — it only counts 15 minutes of active listening.
• Once the cumulative active listening time hits 30 minutes, it triggers an ad.

✅ 4. Background Timer (Even When App is Minimized)