diff --git a/movie_editor/frontend/player.js b/movie_editor/frontend/player.js
index 467938df..ada4c27e 100644
--- a/movie_editor/frontend/player.js
+++ b/movie_editor/frontend/player.js
@@ -117,7 +117,7 @@
   }
 
   function _syncPool() {
-    const urls = new Set(_clips.map((c) => _urlFor(c.media)));
+    const urls = new Set(_clips.filter((c) => c.media).map((c) => _urlFor(c.media)));
     urls.forEach((u) => _ensureVideo(u));
     for (const [u, v] of [...pool]) {
       if (urls.has(u)) continue;
@@ -207,11 +207,18 @@
     const end = _currentClip.startSec + _currentClip.durationSec;
     const next = _clips.find((c) => !c.pending && c.startSec >= end - 0.02 && c !== _currentClip);
     if (!next) { _phSec = end; _pause(); return; }
-    const contiguous = _urlFor(next.media) === _urlFor(_currentClip.media)
-      && Math.abs((next.inSec || 0) - ((_currentClip.inSec || 0) + _currentClip.durationSec)) < 0.05;
+    const prev = _currentClip;
+    const sameSource = next.media && prev.media
+      && _urlFor(next.media) === _urlFor(prev.media);
+    const contiguous = sameSource
+      && Math.abs((next.inSec || 0) - ((prev.inSec || 0) + prev.durationSec)) < 0.05;
     _phSec = next.startSec;
     _currentClip = next;
-    if (!contiguous) _goto(next, 0, _playing);  // jump (different source / non-contiguous)
+    // Reseek on gen-unit / scene boundaries — chain carry scenes overlap in the source file.
+    const needSeek = !sameSource || !contiguous
+      || (next.sceneId && prev.sceneId && next.sceneId !== prev.sceneId)
+      || (next.ghostId && prev.ghostId && next.ghostId !== prev.ghostId);
+    if (needSeek) _goto(next, 0, _playing);
     _notifyPh();
   }
 
@@ -229,7 +236,10 @@
       if (_playing) _raf = requestAnimationFrame(_tick);
       return;
     }
-    if (!_active) return;
+    if (!_active) {
+      if (_playing) _pause();
+      return;
+    }
     const within = _active.currentTime - (_currentClip.inSec || 0);
     if (within >= _currentClip.durationSec - 0.001) { _advance(); }
     else { _phSec = _currentClip.startSec + Math.max(0, within); try { _applyFx(_currentClip, within); } catch (_) {} _notifyPh(); }
diff --git a/movie_editor/frontend/store.js b/movie_editor/frontend/store.js
index 3c958197..d6955fe5 100644
--- a/movie_editor/frontend/store.js
+++ b/movie_editor/frontend/store.js
@@ -552,20 +552,33 @@
     state.sceneGhosts = (state.sceneGhosts || []).filter((g) => !ids.has(g.afterSceneId) && !ids.has(g.id));
   }
 
+  // Pixel overlap between consecutive chain-sampler scenes (carry/i2v guide runs).
+  function _chainOverlapSec(runSceneCount) {
+    if (!runSceneCount || runSceneCount < 2) return 0;
+    const frames = +(state.project?.sampler_inputs?.frame_overlap ?? 16);
+    const fps = state.project?.frame_rate || 25;
+    return Math.max(0, frames / fps);
+  }
+
   function _recordSegment(mediaList, targetSceneIds) {
     if (!mediaList || !mediaList.length || !targetSceneIds || !targetSceneIds.length) return;
     const primary = mediaList.find((m) => m.kind === "videos" || m.kind === "gifs") || mediaList[0];
-    let inAcc = 0;
+    const overlapSec = _chainOverlapSec(targetSceneIds.length);
+    let sourceEnd = 0;
     let clearedRating = false;
     _pruneGhostsAfterRegen(targetSceneIds);
-    for (const id of targetSceneIds) {
+    for (let i = 0; i < targetSceneIds.length; i++) {
+      const id = targetSceneIds[i];
       const sc = scene(id); if (!sc) continue;
-      state.sceneRenders[id] = { media: primary, inSec: inAcc };
+      const prev = i > 0 ? scene(targetSceneIds[i - 1]) : null;
+      const sameUnit = prev && genUnitId(prev) === genUnitId(sc);
+      const inSec = i === 0 ? 0 : (sameUnit ? sourceEnd : Math.max(0, sourceEnd - overlapSec));
+      state.sceneRenders[id] = { media: primary, inSec };
       // New render invalidates the prior RLHF rating — UI shows "— rate —"; server
       // uses continue-refinement (session memory, no new rating) on the next Studio run.
       const root = genUnitRoot(genUnitId(sc));
       if (root && root.rating) { root.rating = ""; clearedRating = true; }
-      inAcc += sceneDurationSec(sc);
+      sourceEnd = inSec + sceneDurationSec(sc);
     }
     if (clearedRating) scheduleSaveSilent();
   }