Music streaming and offline downloads

Design the audio delivery and offline-download system for a music/podcast app with 200M users, where the same track is streamed and also downloaded for offline playback on phones with limited storage and metered data. Streaming must start in well under a second (instant play on tap), gapless playback between tracks is required, offline downloads must survive app kills and reclaim space intelligently, and licensing requires that offline content expire/revalidate. Design the encoding, the streaming start path, and the offline cache + licensing model.