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ADR-0001: WebView-Based Playback

Status

Accepted

Context

Kaset needs to play YouTube Music content, including Premium tracks with DRM protection. There are several approaches to consider:

  1. Direct audio streaming - Download and play audio files directly
  2. AVPlayer with HLS - Use Apple's native player with streaming URLs
  3. Hidden WebView - Load YouTube Music in a WebView and control playback via JavaScript

Direct streaming and AVPlayer approaches cannot handle DRM-protected content. YouTube Music Premium content uses Widevine DRM which requires a browser environment.

Decision

Use a hidden WKWebView (SingletonPlayerWebView) to load YouTube Music's web player at music.youtube.com/watch?v={videoId}. Control playback via JavaScript injection and receive state updates through a JavaScript-to-Swift bridge.

Key implementation details:

  • Single WebView instance shared across the app (singleton pattern)
  • WebView shares cookies with the login WebView for authentication
  • JavaScript bridge sends playback state (isPlaying, progress, duration) to Swift
  • Native controls (PlayerBar, Now Playing) reflect WebView state
  • Background audio continues when window is hidden

Consequences

Positive

  • DRM support - Premium content plays correctly with user's subscription
  • No reverse engineering - Uses official web interface
  • Feature parity - Any content playable on web works in Kaset
  • Authentication reuse - Same cookies as browser login

Negative

  • Resource usage - WebView consumes more memory than native audio
  • Latency - Small delay for JavaScript bridge communication
  • Complexity - JavaScript injection requires careful error handling
  • Testing difficulty - WebView behavior harder to unit test

Mitigations

  • Singleton WebView prevents multiple instances
  • Debounced state updates reduce bridge traffic
  • Dedicated PlayerWebView abstraction isolates WebView concerns