Show animated pulse bar when processing but progress still 0%

For large videos (e.g. 27508 frames), the first 275 frames only amount
to ~1% which rounds to 0 in integer percentage — so detect_pct stays 0
for a while even though the task is actively running. Instead of showing
static zero bars, display a pulsing indeterminate bar with an explanation
message so the user knows the task is alive.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

web/index.html

@@ -458,6 +458,11 @@
   .log-toolbar .subtle { flex: 1; }
   #wl-pause-btn.paused { color: var(--warn); border-color: rgba(181,113,10,.5); }
 
+  @keyframes pulse-bar {
+    0%,100% { opacity:.3; transform: scaleX(.3); }
+    50%      { opacity:1;  transform: scaleX(1);  }
+  }
+
   /* ── Responsive ─────────────────────────────────────────── */
   @media (max-width: 1100px) {
     .shell { grid-template-columns: 1fr; }
@@ -1073,12 +1078,25 @@ function updateDetailDynamic(t) {
       const p = t.download_progress||0;
       progEl.innerHTML = `<div style="font-size:11px;color:var(--muted);margin-bottom:4px">下载进度 ${p}%</div><div class="prog-track"><div class="prog-fill dl" style="width:${p}%"></div></div>`;
     } else if (t.status === 'processing') {
-      progEl.innerHTML = `
-        <div style="display:grid;gap:5px">
-          <div class="phase-row"><span class="phase-label">检测</span><div class="phase-track"><div class="phase-fill detect" style="width:${t.detect_pct||0}%"></div></div><span class="phase-pct">${t.detect_pct||0}%</span></div>
-          <div class="phase-row"><span class="phase-label">处理</span><div class="phase-track"><div class="phase-fill process" style="width:${t.process_pct||0}%"></div></div><span class="phase-pct">${t.process_pct||0}%</span></div>
-          <div class="phase-row"><span class="phase-label">合并</span><div class="phase-track"><div class="phase-fill merge" style="width:${t.merge_pct||0}%"></div></div><span class="phase-pct">${t.merge_pct||0}%</span></div>
-        </div>`;
+      const allZero = !t.detect_pct && !t.process_pct && !t.merge_pct;
+      if (allZero) {
+        // 尚未有实质进度，显示脉冲动画表示"正在工作"
+        progEl.innerHTML = `
+          <div style="font-size:11px;color:var(--warn);margin-bottom:6px">
+            ⏳ 初始化中，正在处理第一批帧…（大视频需要等待）
+          </div>
+          <div class="prog-track" style="overflow:visible">
+            <div style="height:4px;border-radius:2px;background:linear-gradient(90deg,var(--brand),#0ea5a5);
+              animation:pulse-bar 1.5s ease-in-out infinite;transform-origin:left"></div>
+          </div>`;
+      } else {
+        progEl.innerHTML = `
+          <div style="display:grid;gap:5px">
+            <div class="phase-row"><span class="phase-label">检测</span><div class="phase-track"><div class="phase-fill detect" style="width:${t.detect_pct||0}%"></div></div><span class="phase-pct">${t.detect_pct||0}%</span></div>
+            <div class="phase-row"><span class="phase-label">处理</span><div class="phase-track"><div class="phase-fill process" style="width:${t.process_pct||0}%"></div></div><span class="phase-pct">${t.process_pct||0}%</span></div>
+            <div class="phase-row"><span class="phase-label">合并</span><div class="phase-track"><div class="phase-fill merge" style="width:${t.merge_pct||0}%"></div></div><span class="phase-pct">${t.merge_pct||0}%</span></div>
+          </div>`;
+      }
     } else {
       progEl.innerHTML = '';
     }