Music daemon + cross-source sync via OBS WebSocket

Music persistence across scene switches by extracting playback into a
separate browser source (music/index.html) — single source instance
shared across scenes via OBS's "Add Existing", so it doesn't restart on
scene change.

Loading and Game overlays subscribe to mpd:state CustomEvents over OBS
WebSocket; the daemon broadcasts at 1 Hz plus on every track change.
File-based command pipeline lets bash control playback without a
WebSocket client of its own:

- vendor/obs-ws-mini.js — minimal WS v5 client with HMAC-SHA256 auth,
  hard timeout, close-rejection, and a pure-JS SHA-256 fallback for
  CEF file:// origins where crypto.subtle is unavailable.
- setup.sh — generates vendor/obs-config.js from the OBS plugin config;
  checks the live socket instead of the (lagging) config file.
- music/index.html — invisible audio worker. Plays through a shuffled
  queue with hardened error/stall recovery, polls loading/cmd.js for
  bash-issued commands, broadcasts mpd:state via WS. Includes a
  diagnostic status block (visible if the source's eye-icon is on).
- loading/index.html — strips local audio playback; subscribes to
  mpd:state to drive the now-playing terminal line live. Removes the
  redundant trailing prompt; terminal lines anchor at the bottom.
- loading/playlist.sh — rebuilt as subcommand API:
    sync (default), skip, prev, pause, resume, status
  control commands write loading/cmd.js (id, type, ts), which the
  daemon polls every 250ms.
- loading/convert.sh — strips video tracks from .webm music downloads
  to audio-only m4a (~95% smaller, ~20× faster decode); fixes the
  CPU pegging from CEF decoding 1080p VP9 video for music playback.
- .gitignore — track manifests, ignore generated wrappers + secrets +
  the audio cache.

loading/convert.sh

@@ -0,0 +1,80 @@
+#!/usr/bin/env bash
+# loading/convert.sh — strip video tracks out of audio files in
+# ~/.config/obs-studio/playlist/ and re-encode to AAC m4a in place.
+#
+# WHY: yt-dlp .webm downloads include 1080p video. Chromium's <audio>
+# element decodes the video stream too (just doesn't render it) — pegs
+# CPU and stalls playback mid-track. Audio-only m4a is ~95% smaller
+# and decodes ~20× faster.
+#
+#   ./convert.sh             — convert all video-bearing files
+#   ./convert.sh --dry-run   — show what would happen, do nothing
+#
+# DO NOT run this while OBS has a playlist track open (between streams
+# is fine; mid-stream you'll lock the file ffmpeg is reading from).
+#
+# After conversion, re-index:  ./playlist.sh
+set -euo pipefail
+
+DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+OBS_DIR="$(cd "$DIR/.." && pwd)"
+AUDIO_DIR="$OBS_DIR/playlist"
+
+DRY=0
+[[ "${1:-}" == "--dry-run" ]] && DRY=1
+
+if [[ ! -d "$AUDIO_DIR" ]]; then
+  echo "  ✗ $AUDIO_DIR does not exist" >&2
+  exit 1
+fi
+if ! command -v ffprobe >/dev/null 2>&1 || ! command -v ffmpeg >/dev/null 2>&1; then
+  echo "  ✗ ffmpeg / ffprobe required" >&2
+  exit 1
+fi
+
+shopt -s nullglob nocaseglob
+
+# Files that contain a video stream (and aren't already m4a)
+declare -a TODO=()
+for f in "$AUDIO_DIR"/*.{webm,mp4,mkv,mov,avi}; do
+  [[ -f "$f" ]] || continue
+  # Skip yt-dlp intermediate files
+  case "$(basename "$f")" in
+    *.f[0-9]*.*|*.temp.*|*.part) continue ;;
+  esac
+  # Only consider files that actually contain a video stream
+  if ffprobe -v error -select_streams v -show_entries stream=codec_type \
+       -of csv=p=0 "$f" 2>/dev/null | grep -q video; then
+    TODO+=("$f")
+  fi
+done
+
+if [[ ${#TODO[@]} -eq 0 ]]; then
+  echo "  ✓ nothing to convert (no video-bearing files in $AUDIO_DIR)"
+  exit 0
+fi
+
+echo "── Converting ${#TODO[@]} file(s) → AAC m4a ──"
+for f in "${TODO[@]}"; do
+  base="${f%.*}"
+  out="$base.m4a"
+  if [[ -f "$out" ]]; then
+    echo "  ⊘ skip (m4a exists): $(basename "$f")"
+    continue
+  fi
+  echo "  → $(basename "$f")"
+  if [[ $DRY -eq 1 ]]; then
+    echo "    (dry-run: would write $(basename "$out") and remove the source)"
+    continue
+  fi
+  if ffmpeg -nostdin -loglevel error -i "$f" -vn -c:a aac -b:a 192k "$out"; then
+    rm -f "$f"
+    echo "    ✓ ${out##*/}  ($(du -h "$out" | cut -f1))"
+  else
+    echo "    ✗ ffmpeg failed; leaving $(basename "$f") in place" >&2
+    rm -f "$out"
+  fi
+done
+
+echo
+echo "  → next: ./playlist.sh   (re-index for the new filenames)"