Which technological innovation was most critical to enabling modern music streaming services like Spotify and Apple Music?

The music industry has undergone massive transformation through technological innovations. Streaming platforms completely changed how we consume music, but do you know which groundbreaking technology first enabled the modern streaming revolution? Test your knowledge of the critical product innovation that made today's music streaming landscape possible.

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The MP3 compression algorithm (1993)
Apple's iPod hardware (2001)
Dolby Digital sound encoding (1986)
MIDI protocol for instrument connection (1983)