add readme

Author: Alex2772

examples/audio/synced/README.md

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+# Audio synced playback
+
+<!-- aui:example audio -->
+Demonstrates synchronized playback of multiple audio tracks with per-track volume and a simple visual gain meter.
+
+- Choose a sample set with radio buttons; each set contains a base layer and additional layers.
+- Control playback with Play/Pause and toggle Loop to automatically restart when tracks finish.
+- Each track row shows:
+    - A small color bar reflecting recent amplitude changes (greener = higher activity).
+    - A volume slider (0–100%) applied in real time.
+
+When any track finishes, the example resets all tracks to keep them aligned. If Loop is enabled, playback restarts
+immediately.
+
+## UI
+
+- Playback controls: Play, Pause, Loop.
+- Sample selector: radio group to switch between predefined layered samples.
+- Tracks panel: rows for each layer with activity indicator and volume slider.
+
+## Concepts
+
+- Synchronized start/stop across multiple audio players.
+- Reactive state for play/pause, loop, selection, and per-track volume.
+- Lightweight visual gain analysis for a live activity indicator.