The MUXL live-HLS window and WebRTCPlayback2 have superseded the legacy GStreamer concatenation playback, leaving these unreachable: - ConcatStream (concat.go): only referenced by commented-out progressive.go experiments. - WebRTCPlayback (webrtc_playback.go): the new-webrtc-playback flag has defaulted to true (WebRTCPlayback2, which consumes pre-packetized segments off the bus). Drop the old path and the vestigial flag. - progressive.go: fully commented-out MP4Playback/MKVPlayback that only drove ConcatStream. HandleWebRTCPlayback now always calls WebRTCPlayback2. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>