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I Built a Spotify to MP3 Converter — Here's the Stack

#spotify #webdev #opensource #showdev

A technical deep-dive into building a fast, free Spotify downloader that actually works.

Every developer who's tried building a Spotify downloader hits the same wall: Spotify doesn't want you doing this. Their API doesn't expose audio files, and their streams are encrypted with Widevine DRM.

Here's how I built Spodown — a free Spotify-to-MP3 converter that handles thousands of downloads daily.

The Architecture 

User paste Spotify link
    ↓
Backend resolves track metadata (name, artist, duration)
    ↓
YouTube Music search → find matching audio
    ↓
yt-dlp extracts audio stream
    ↓
ffmpeg transcodes to MP3/FLAC
    ↓
Serve file to user
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Simple in theory. The devil is in the details.

Stack

  • Frontend: Vue 3 + TypeScript + PWA
  • Backend: Go + Fiber
  • Matching: Custom YouTube Music search scoring
  • Download: yt-dlp with residential proxy rotation
  • Transcoding: ffmpeg
  • Cache: MediaFire/VK document storage
  • Queue: In-memory job system with SSE progress

The Matching Problem

The hardest part isn't downloading — it's finding the right audio. Spotify track metadata needs to match YouTube Music results, and the matching has to be really good or users get wrong songs.

I built a scoring system that compares:

  • Track name (exact > partial > fuzzy)
  • Artist name
  • Duration (±3 seconds tolerance)
  • Album name (when available)

Only candidates scoring above a threshold get accepted. Below that, we return "not found" rather than a wrong song.

The Widevine Path

For tracks that YouTube doesn't have (rare songs, new releases), I built a fallback: Widevine CDM decryption. This decrypts Spotify's own AAC streams directly — it's what the official Spotify Web Player does, just automated.

What I Learned

  1. Caching is everything — 70% of downloads are repeat requests. Store results, skip the pipeline.
  2. Rate limits are real — both Spotify and YouTube throttle. Rotating proxies and account pools are essential.
  3. Users want simplicity — "paste link → get file" beats any feature list.
  4. SEO matters — technical tool ≠ invisible. I built the site server-rendered with proper meta tags so search engines could index it.

Try It

Spodown — free tier needs no account. PRO unlocks 320kbps/FLAC if you want max quality.

Questions? Drop them in the comments — happy to go deeper on any part.

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