Use visible YouTube player for song preview (ToS compliance)

Preview now uses YouTube IFrame API with a visible 240x135 player in the
top-left corner of the song select screen, matching the game page layout.
Falls back to local audio for songs without YouTube config.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/features/song-select/SongSelectScreen.css

@@ -56,6 +56,27 @@
   opacity: 0.35;
 }
 
+.song-select-screen__yt-preview {
+  position: fixed;
+  top: 12px;
+  left: 12px;
+  width: 240px;
+  height: 135px;
+  z-index: 10;
+  border-radius: 10px;
+  overflow: hidden;
+  border: 2px solid rgba(255, 255, 255, 0.15);
+  box-shadow: 0 4px 20px rgba(0, 0, 0, 0.6);
+  pointer-events: none;
+}
+
+.song-select-screen__yt-preview iframe {
+  display: block;
+  width: 100%;
+  height: 100%;
+  border: 0;
+}
+
 .song-select-screen__content {
   position: relative;
   z-index: 2;

src/features/song-select/SongSelectScreen.tsx

@@ -1,4 +1,4 @@
-import { useMemo, useState } from 'react'
+import { useMemo, useRef, useState } from 'react'
 import type { CSSProperties } from 'react'
 import { useNavigate } from 'react-router-dom'
 import { useGameInput } from '../../input/useGameInput'
@@ -26,8 +26,9 @@ export function SongSelectScreen() {
   const resetStats = useGameStatsStore((state) => state.resetStats)
   const [currentIndex, setCurrentIndex] = useState(0)
   const activeSong = SONGS[currentIndex]
+  const ytPreviewRef = useRef<HTMLDivElement>(null)
 
-  useSongPreview(activeSong)
+  useSongPreview(activeSong, ytPreviewRef.current)
 
   const handleConfirm = () => {
     setCurrentSong(activeSong)
@@ -74,6 +75,8 @@ export function SongSelectScreen() {
         difficulty={activeSong.difficulty}
       />
 
+      <div ref={ytPreviewRef} className="song-select-screen__yt-preview" />
+
       <div className="song-select-screen__content">
         <header className="song-select-screen__header">
           <span className="song-select-screen__disco-ball" aria-hidden="true" />

src/features/song-select/useSongPreview.ts

@@ -6,19 +6,21 @@ const PREVIEW_DELAY_MS = 300
 const PREVIEW_START_SEC = 30
 const FADE_IN_MS = 1000
 const FADE_STEP_MS = 50
-const FADE_OUT_MS = 400
 const MAX_VOLUME = 0.5
 
-export function useSongPreview(song: Song) {
+/**
+ * Plays a song preview. For YouTube songs, mounts a player into `ytHostEl`.
+ * The caller must render a visible container and pass it via ref.
+ */
+export function useSongPreview(song: Song, ytHostEl: HTMLElement | null) {
   const cleanupRef = useRef<(() => void) | null>(null)
 
   useEffect(() => {
-    // Fade out + destroy previous preview
     cleanupRef.current?.()
     cleanupRef.current = null
 
-    if (song.youtubeVideoId) {
-      const cleanup = startYouTubePreview(song)
+    if (song.youtubeVideoId && ytHostEl) {
+      const cleanup = startYouTubePreview(song, ytHostEl)
       cleanupRef.current = cleanup
       return cleanup
     }
@@ -26,11 +28,11 @@ export function useSongPreview(song: Song) {
     const cleanup = startLocalPreview(song)
     cleanupRef.current = cleanup
     return cleanup
-  }, [song.id])
+  }, [song.id, ytHostEl])
 }
 
 // ---------------------------------------------------------------------------
-// Local audio preview (existing approach)
+// Local audio preview
 // ---------------------------------------------------------------------------
 
 function startLocalPreview(song: Song): () => void {
@@ -62,28 +64,21 @@ function startLocalPreview(song: Song): () => void {
 }
 
 // ---------------------------------------------------------------------------
-// YouTube preview
+// YouTube preview (visible player)
 // ---------------------------------------------------------------------------
 
-function startYouTubePreview(song: Song): () => void {
+function startYouTubePreview(song: Song, host: HTMLElement): () => void {
   let destroyed = false
   let player: YT.Player | null = null
   let fadeIv = 0
-  let host: HTMLDivElement | null = null
+
+  // Clear any previous player content
+  host.innerHTML = ''
 
   const timer = window.setTimeout(() => {
     loadYouTubeApi().then(() => {
       if (destroyed) return
 
-      // Create an off-screen container for the iframe
-      host = document.createElement('div')
-      Object.assign(host.style, {
-        position: 'fixed', width: '1px', height: '1px',
-        opacity: '0', pointerEvents: 'none', overflow: 'hidden',
-        top: '-10px', left: '-10px',
-      })
-      document.body.appendChild(host)
-
       const div = document.createElement('div')
       host.appendChild(div)
 
@@ -92,8 +87,8 @@ function startYouTubePreview(song: Song): () => void {
 
       player = new YT.Player(div, {
         videoId: song.youtubeVideoId!,
-        width: '1',
-        height: '1',
+        width: '100%',
+        height: '100%',
         playerVars: {
           autoplay: 1,
           controls: 0,
@@ -114,7 +109,6 @@ function startYouTubePreview(song: Song): () => void {
           onStateChange(e: YT.OnStateChangeEvent) {
             if (destroyed || !player) return
             if (e.data === YT.PlayerState.PLAYING) {
-              // Fade in
               const maxVol = MAX_VOLUME * 100
               const step = (maxVol * FADE_STEP_MS) / FADE_IN_MS
               fadeIv = window.setInterval(() => {
@@ -138,23 +132,9 @@ function startYouTubePreview(song: Song): () => void {
     destroyed = true
     clearTimeout(timer)
     clearInterval(fadeIv)
-    // Fade out quickly then destroy
     if (player) {
-      const p = player
-      const maxVol = p.getVolume()
-      const step = (maxVol * FADE_STEP_MS) / FADE_OUT_MS
-      const outIv = window.setInterval(() => {
-        const cur = p.getVolume()
-        if (cur - step <= 0) {
-          clearInterval(outIv)
-          try { p.destroy() } catch { /* ignore */ }
-          host?.remove()
-        } else {
-          p.setVolume(cur - step)
-        }
-      }, FADE_STEP_MS)
-    } else {
-      host?.remove()
+      try { player.destroy() } catch { /* ignore */ }
     }
+    host.innerHTML = ''
   }
 }