Spotify — Notes

Functional

• Catalog of music + podcasts.
• Streaming playback (multi-device).
• Playlists (personal, collaborative, algorithmic).
• Recommendations (Discover Weekly, Daily Mix, Release Radar).
• Search, social sharing.
• Offline downloads.
• Spotify Connect (device handoff).

Non-functional

• 600M+ MAU, 200M+ premium.
• p99 first audio < 500 ms.
• 99.99% playback availability.

Capacity

• Tens of millions of tracks; each in 3-5 bitrates × few codecs.
• ~5 PB total catalog after multi-encode (much smaller than video CDN).
• 1B+ streams/day; royalty pipeline batch nightly.

Schema

• tracks(id, album_id, artists[], duration_ms, isrc, audio_files[])
• playlists(id, owner, collaborative, item_order[])
• streams(user_id, track_id, ts, source, duration_ms) Kafka topic for events
• taste_profile(user_id, vec)

Trade-offs

• Many small files for albums; CDN cache hit rate critical.
• Hi-Fi (lossless) explodes bandwidth — gated by subscription.
• Per-stream royalty model demands precise accounting; need idempotent stream logging.
• Podcast model differs: exclusive shows, ads (DAI), serving with different SLAs.

Refs

• Spotify Engineering blog (Apollo, Backstage, Discover Weekly explainers), "The Spotify Recommendation Stack" talks, ByteByteGo "Design Spotify", Alex Xu Vol 2.