Stop asking for HEVC on devices without hardware decode and fall back when frames drop

frontend/app.js

@@ -105,8 +105,17 @@ function saveDataToStorage(jsonStr) {
 // is the browser's own claim; if a copy still fails to play here, the device
 // is remembered (NO_HEVC_KEY) and stops asking — it gets H.264 as before.
 const NO_HEVC_KEY = 'ytpNoHevc';
+// canPlayType only says the browser can decode HEVC — often in software, which
+// stutters the picture while the audio stays fine. Ask MediaCapabilities whether
+// it is hardware-accelerated (powerEfficient) and smooth; remember the answer.
+const HEVC_HW_KEY = 'ytpHevcHw';
+try {
+  navigator.mediaCapabilities.decodingInfo({ type: 'file', video: { contentType: 'video/mp4; codecs="hvc1.1.6.L93.B0"', width: 1280, height: 720, bitrate: 1500000, framerate: 30 } })
+    .then((i) => { try { localStorage.setItem(HEVC_HW_KEY, i.supported && i.smooth && i.powerEfficient ? '1' : '0'); } catch { /* storage blocked */ } })
+    .catch(() => {});
+} catch { /* no MediaCapabilities */ }
 function hevcCapable() {
-  try { if (localStorage.getItem(NO_HEVC_KEY) === '1') return false; } catch { /* storage blocked */ }
+  try { if (localStorage.getItem(NO_HEVC_KEY) === '1' || localStorage.getItem(HEVC_HW_KEY) === '0') return false; } catch { /* storage blocked */ }
   try {
     return document.createElement('video').canPlayType('video/mp4; codecs="hvc1.1.6.L93.B0"') !== '';
   } catch { return false; }
@@ -2013,6 +2022,36 @@ document.addEventListener('play', () => {
   preload(m, { quiet: true });
 }, true);
 
+// Dropped-frame watchdog: an HEVC server copy that this device decodes in
+// software drops frames while the audio plays on. Sample the first ~30 s of
+// each play; if it is clearly struggling, stop asking this device for HEVC and
+// restart the song on the compatible stream, from where it is.
+{
+  const dropWatch = { id: '', t: 0, tries: 0 };
+  document.addEventListener('playing', (e) => {
+    const v = e.target;
+    if (!v || v.tagName !== 'VIDEO' || !current || !current.meta || !v.getVideoPlaybackQuality) return;
+    if (!(current.qualities || []).some((q) => q.codec === 'hevc') || !current.serverCached) return;
+    if (dropWatch.id === current.meta.id && dropWatch.tries >= 6) return;
+    if (dropWatch.id !== current.meta.id) { dropWatch.id = current.meta.id; dropWatch.tries = 0; }
+    const id = current.meta.id, at = v.getVideoPlaybackQuality(), t0 = Date.now();
+    const check = setInterval(() => {
+      if (!current || !current.meta || current.meta.id !== id || v.paused || Date.now() - t0 > 30000) { clearInterval(check); return; }
+      dropWatch.tries++;
+      const q = v.getVideoPlaybackQuality();
+      const total = q.totalVideoFrames - at.totalVideoFrames, dropped = q.droppedVideoFrames - at.droppedVideoFrames;
+      if (total >= 60 && dropped / total > 0.2) {
+        clearInterval(check);
+        try { localStorage.setItem(NO_HEVC_KEY, '1'); } catch { /* storage blocked */ }
+        toast('Video was choppy on this device — switching to the compatible format.', { duration: 4000 });
+        const pos = v.currentTime || 0;
+        if (pos > 1 && data.resumePositions && rememberPosEnabled()) data.resumePositions[id] = Math.floor(pos);
+        Player.loadVideo(current.meta, { preferStream: true, nocache: true, resume: true, reveal: false });
+      }
+    }, 3000);
+  }, true);
+}
+
 
 // ============================================================================
 // Video editor — cut parts out of a video and save a custom offline copy