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Spotify HLD: Streaming Audio That Starts Fast and Never Stalls

A Spotify system design: storing audio as a chunked bitrate ladder in object storage behind a CDN, adaptive bitrate selection from bandwidth and buffer, the metadata model, and play history at scale.

By fiveyearsdevJune 14, 20269 min read

"Design Spotify." The catalog, playlists, and likes are a tidy CRUD app you could finish before lunch. The thing that makes it Spotify — and the thing an interviewer actually wants — is audio that starts the instant you hit play and never stutters, for hundreds of millions of listeners on every kind of network from fibre to a phone in a tunnel. That's not a database problem. It's a storage-and-delivery problem, and it has a beautiful, self-contained core: the bitrate ladder and adaptive streaming. The two facts that shape everything: audio files are large immutable blobs (so they live in objec…

What’s inside

Let's start nowhere near a computer

Where this exact shape shows up

Step 1 — Functional requirements (sentences first)

Step 2 — Non-functional requirements

Step 3 — The data model, and where bytes live

Step 4 — The core: adaptive bitrate keeps the tank full

Step 5 — Verbs become APIs (the API design)

Step 6 — Trade-offs (each one keeping an NFR)

The complete implementation

Step 7 — Only now, the boxes

Step 8 — Scaling the design, one bottleneck at a time

Step 9 — When a piece fails: designing for failure

The interview corner

Where to go from here

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