- Wrap HTML5 <audio> in AudioContext + MediaElementAudioSourceNode in
LocalAudioPlayer.js (non-breaking; falls back gracefully)
- Add enableSmartSpeed: false to user settings store (client-side)
- Add SMART_SPEED_PHASE1_DESIGN.md design document
Firefox, at least, supports playing `matroska/audio` containers natively but
the client was not checking for support. Clients that do not support
playing `matroska/audio` containers will fallback to transcoding.