diff --git a/services/web-ui/public/js/timecode.js b/services/web-ui/public/js/timecode.js
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+++ b/services/web-ui/public/js/timecode.js
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+// services/web-ui/public/js/timecode.js
+// 59.94 fps drop-frame timecode utilities.
+// Exposes: window.TC
+
+(function (global) {
+  'use strict';
+
+  // 59.94 = 60000/1001
+  const FPS_EXACT      = 60000 / 1001;
+  const NOM            = 60;   // nominal integer fps
+  const DROP           = 4;    // frames dropped per minute (except every 10th)
+  const FRAMES_PER_MIN   = NOM * 60 - DROP;          // 3596
+  const FRAMES_PER_10MIN = FRAMES_PER_MIN * 10 + DROP; // 35964
+  const FRAMES_PER_HOUR  = FRAMES_PER_10MIN * 6;     // 215784
+
+  function pad2(n) { return String(Math.floor(n)).padStart(2, '0'); }
+
+  /**
+   * Convert a frame count to a 59.94 DF timecode string: HH:MM:SS;FF
+   */
+  function framesToTC(totalFrames) {
+    const fc  = Math.max(0, Math.round(totalFrames));
+    const h   = Math.floor(fc / FRAMES_PER_HOUR);
+    let rem   = fc % FRAMES_PER_HOUR;
+    const tm  = Math.floor(rem / FRAMES_PER_10MIN); // tens of minutes (0–5)
+    rem       = rem % FRAMES_PER_10MIN;
+    let m     = 0;
+    if (rem >= DROP) {
+      m   = Math.floor((rem - DROP) / FRAMES_PER_MIN) + 1;
+      rem = (rem - DROP) % FRAMES_PER_MIN;
+    }
+    const M  = tm * 10 + m;
+    const s  = Math.floor(rem / NOM);
+    const ff = rem % NOM;
+    return `${pad2(h)}:${pad2(M)}:${pad2(s)};${pad2(ff)}`;
+  }
+
+  /**
+   * Convert a 59.94 DF timecode string (HH:MM:SS;FF or HH:MM:SS:FF) to frame count.
+   */
+  function tcToFrames(tc) {
+    if (!tc) return 0;
+    const clean = String(tc).replace(';', ':');
+    const parts = clean.split(':').map(Number);
+    if (parts.length !== 4) return 0;
+    const [h, m, s, f] = parts;
+    const totalMinutes = h * 60 + m;
+    return (NOM * 3600 * h)
+         + (NOM * 60   * m)
+         + (NOM        * s)
+         +  f
+         - DROP * (totalMinutes - Math.floor(totalMinutes / 10));
+  }
+
+  /**
+   * Convert seconds (float) → frame count at 59.94.
+   */
+  function secondsToFrames(seconds) {
+    return Math.round(seconds * FPS_EXACT);
+  }
+
+  /**
+   * Convert frame count → seconds (float) at 59.94.
+   */
+  function framesToSeconds(frames) {
+    return frames / FPS_EXACT;
+  }
+
+  global.TC = {
+    framesToTC,
+    tcToFrames,
+    secondsToFrames,
+    framesToSeconds,
+    FPS: FPS_EXACT,
+  };
+
+})(window);