diff --git a/services/web-ui/public/js/timecode.js b/services/web-ui/public/js/timecode.js
index e7bebe4..52f0181 100644
--- a/services/web-ui/public/js/timecode.js
+++ b/services/web-ui/public/js/timecode.js
@@ -6,33 +6,49 @@
   '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
+  const FPS_EXACT        = 60000 / 1001;
+  const NOM              = 60;   // nominal integer fps
+  const DROP             = 4;    // frames dropped per minute (except every 10th)
+  const FRAMES_FIRST_MIN = NOM * 60;                    // 3600 – non-drop minute
+  const FRAMES_PER_MIN   = NOM * 60 - DROP;             // 3596 – drop minute
+  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
+   *
+   * Each 10-minute group contains one non-drop minute (3600 frames) followed
+   * by nine drop minutes (3596 frames each).  Frame numbers 0–3 are skipped at
+   * the start of every drop minute; we account for this by shifting the
+   * within-minute frame index by DROP when computing 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)
+    const tm  = Math.floor(rem / FRAMES_PER_10MIN); // tens-of-minutes group (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;
+
+    let m, ss, ff;
+    if (rem < FRAMES_FIRST_MIN) {
+      // First minute of the 10-min group — no frame drop
+      m  = 0;
+      ss = Math.floor(rem / NOM);
+      ff = rem % NOM;
+    } else {
+      // Minutes 1–9: frame numbers 0–3 at second :00 are skipped
+      rem -= FRAMES_FIRST_MIN;
+      m   = Math.floor(rem / FRAMES_PER_MIN) + 1;
+      const remInMin = rem % FRAMES_PER_MIN;
+      // Shift by DROP so the label starts at :00;04 instead of :00;00
+      const adj = remInMin + DROP;
+      ss  = Math.floor(adj / NOM);
+      ff  = adj % NOM;
     }
-    const M  = tm * 10 + m;
-    const s  = Math.floor(rem / NOM);
-    const ff = rem % NOM;
-    return `${pad2(h)}:${pad2(M)}:${pad2(s)};${pad2(ff)}`;
+    const M = tm * 10 + m;
+    return `${pad2(h)}:${pad2(M)}:${pad2(ss)};${pad2(ff)}`;
   }
 
   /**