diff --git a/frontend/src/pages/constructor.tsx b/frontend/src/pages/constructor.tsx
index 40796d5..f31f35d 100644
--- a/frontend/src/pages/constructor.tsx
+++ b/frontend/src/pages/constructor.tsx
@@ -239,53 +239,6 @@ const getAssetLabel = (asset: ProjectAsset) => {
 const getAssetSourceValue = (asset: ProjectAsset) =>
   String(asset.storage_key || asset.cdn_url || '').trim();
 
-const extractPrivateUrlFromDownloadPath = (value: string) => {
-  const normalized = String(value || '').trim();
-  if (!normalized) return '';
-
-  try {
-    const parsed = new URL(normalized, 'http://localhost');
-    const privateUrl = parsed.searchParams.get('privateUrl');
-    return String(privateUrl || '').trim();
-  } catch (error) {
-    console.error('Failed to parse download URL:', error);
-    return '';
-  }
-};
-
-const extractS3ObjectKey = (value: string) => {
-  const normalized = String(value || '').trim();
-  if (!normalized) return '';
-
-  try {
-    const parsed = new URL(normalized);
-    const hostname = String(parsed.hostname || '').toLowerCase();
-    if (
-      !hostname.includes('amazonaws.com') &&
-      !hostname.includes('cloudfront.net')
-    )
-      return '';
-    const decodedPath = decodeURIComponent(
-      String(parsed.pathname || '').replace(/^\/+/, ''),
-    );
-    if (!decodedPath) return '';
-
-    const pathParts = decodedPath.split('/').filter(Boolean);
-    if (pathParts.length <= 1) return decodedPath;
-
-    const firstPart = pathParts[0];
-    const isLikelyStoragePrefix = /^[a-f0-9]{24,64}$/i.test(firstPart);
-    if (isLikelyStoragePrefix) {
-      return pathParts.slice(1).join('/');
-    }
-
-    return decodedPath;
-  } catch (error) {
-    console.error('Failed to parse S3 asset URL:', error);
-    return '';
-  }
-};
-
 const formatDurationNote = (durationSec?: number | string | null) => {
   const parsed = Number(durationSec);
   if (!Number.isFinite(parsed) || parsed <= 0) return 'Duration: unknown';
@@ -310,19 +263,8 @@ const resolveAssetPlaybackUrl = (value?: string) => {
   if (normalized.startsWith('/file/download'))
     return `${baseURLApi}${normalized}`;
 
-  if (normalized.startsWith('http://') || normalized.startsWith('https://')) {
-    const downloadPrivateUrl = extractPrivateUrlFromDownloadPath(normalized);
-    if (downloadPrivateUrl) {
-      return `${baseURLApi}/file/download?privateUrl=${encodeURIComponent(downloadPrivateUrl)}`;
-    }
-
-    const s3ObjectKey = extractS3ObjectKey(normalized);
-    if (s3ObjectKey) {
-      return `${baseURLApi}/file/download?privateUrl=${encodeURIComponent(s3ObjectKey)}`;
-    }
-
+  if (normalized.startsWith('http://') || normalized.startsWith('https://'))
     return normalized;
-  }
 
   const normalizedPrivateUrl = normalized.replace(/^\/+/, '');
   return `${baseURLApi}/file/download?privateUrl=${encodeURIComponent(normalizedPrivateUrl)}`;
@@ -2364,7 +2306,18 @@ const ConstructorPage = ({ mode = 'constructor' }: ConstructorPageProps) => {
     const video = transitionVideoRef.current;
     if (!transitionPreview || !video) return;
 
-    let fallbackTimer: ReturnType<typeof setTimeout> | null = null;
+    let startWatchdogTimer: ReturnType<typeof setTimeout> | null = null;
+    let finishTimer: ReturnType<typeof setTimeout> | null = null;
+    let hardTimeoutTimer: ReturnType<typeof setTimeout> | null = null;
+    let previewBlobUrl: string | null = null;
+    let didFinish = false;
+    let didStartPlayback = false;
+
+    const sourceCandidateRaw =
+      transitionPreview.reverseMode === 'separate'
+        ? transitionPreview.reverseVideoUrl || ''
+        : transitionPreview.videoUrl;
+    const sourceUrl = resolveAssetPlaybackUrl(sourceCandidateRaw);
 
     const cleanupReverseFrame = () => {
       if (reverseAnimationFrame.current !== null) {
@@ -2373,8 +2326,74 @@ const ConstructorPage = ({ mode = 'constructor' }: ConstructorPageProps) => {
       }
     };
 
-    const finishPreview = () => {
+    const clearTimers = () => {
+      if (startWatchdogTimer) clearTimeout(startWatchdogTimer);
+      if (finishTimer) clearTimeout(finishTimer);
+      if (hardTimeoutTimer) clearTimeout(hardTimeoutTimer);
+      startWatchdogTimer = null;
+      finishTimer = null;
+      hardTimeoutTimer = null;
+    };
+
+    const cleanupPreviewBlobUrl = () => {
+      if (!previewBlobUrl) return;
+      URL.revokeObjectURL(previewBlobUrl);
+      previewBlobUrl = null;
+    };
+
+    const shouldLoadTransitionViaBlob = (candidateUrl: string) => {
+      try {
+        const parsedUrl = new URL(candidateUrl, window.location.origin);
+        const isSameOrigin = parsedUrl.origin === window.location.origin;
+        if (!isSameOrigin) return false;
+        return (
+          parsedUrl.pathname === '/api/file/download' ||
+          parsedUrl.pathname === '/file/download'
+        );
+      } catch (error) {
+        console.error('Transition preview URL parsing failed:', {
+          candidateUrl,
+          error,
+        });
+        return false;
+      }
+    };
+
+    const buildBlobRequestUrl = (candidateUrl: string) => {
+      if (candidateUrl.startsWith('/api/')) {
+        return candidateUrl.replace(/^\/api(?=\/)/, '');
+      }
+      return candidateUrl;
+    };
+
+    const resolvePlayableTransitionSource = async () => {
+      cleanupPreviewBlobUrl();
+
+      if (!shouldLoadTransitionViaBlob(sourceUrl)) {
+        return sourceUrl;
+      }
+
+      const token =
+        typeof window !== 'undefined' ? localStorage.getItem('token') || '' : '';
+      const requestUrl = buildBlobRequestUrl(sourceUrl);
+      const response = await axios.get(requestUrl, {
+        responseType: 'blob',
+        headers: token ? { Authorization: `Bearer ${token}` } : undefined,
+      });
+
+      previewBlobUrl = URL.createObjectURL(response.data);
+      return previewBlobUrl;
+    };
+
+    const finishPreview = (reason: string) => {
+      if (didFinish) return;
+      didFinish = true;
+      clearTimers();
       cleanupReverseFrame();
+      video.pause();
+      video.removeAttribute('src');
+      video.load();
+      cleanupPreviewBlobUrl();
       setTransitionPreview(null);
       setPendingNavigationPageId((pendingPageId) => {
         const nextPageId = String(pendingPageId || '').trim();
@@ -2386,25 +2405,59 @@ const ConstructorPage = ({ mode = 'constructor' }: ConstructorPageProps) => {
         }
         return '';
       });
+      console.info('Transition preview finished:', {
+        reason,
+        src: video.currentSrc || sourceUrl || '',
+      });
     };
 
-    const configuredDurationMs =
-      (transitionPreview.durationSec && transitionPreview.durationSec > 0
-        ? transitionPreview.durationSec
-        : 0.7) * 1000;
+    const configuredDurationSec = Number(transitionPreview.durationSec);
+    const getMediaErrorDetails = () => {
+      if (!video.error) return null;
+      const mediaError = video.error as MediaError & { message?: string };
+      return {
+        code: mediaError.code,
+        message: mediaError.message || '',
+      };
+    };
+
+    const logTransitionIssue = (reason: string, error?: unknown) => {
+      console.error('Transition preview issue:', {
+        reason,
+        src: video.currentSrc || sourceUrl || '',
+        readyState: video.readyState,
+        networkState: video.networkState,
+        duration: video.duration,
+        configuredDurationSec: transitionPreview.durationSec,
+        reverseMode: transitionPreview.reverseMode,
+        mediaError: getMediaErrorDetails(),
+        error,
+      });
+    };
+
+    const scheduleFinishByDuration = (durationSec: number) => {
+      if (!Number.isFinite(durationSec) || durationSec <= 0 || finishTimer) {
+        return;
+      }
+      finishTimer = setTimeout(() => {
+        finishPreview('duration-timer');
+      }, durationSec * 1000 + 200);
+    };
 
     const runReversePreview = () => {
       cleanupReverseFrame();
       const duration =
         Number.isFinite(video.duration) && video.duration > 0
           ? video.duration
-          : Math.max(configuredDurationMs / 1000, 0.7);
+          : Number.isFinite(configuredDurationSec) && configuredDurationSec > 0
+            ? configuredDurationSec
+            : 0.7;
       const reverseSeconds =
-        transitionPreview.durationSec && transitionPreview.durationSec > 0
-          ? transitionPreview.durationSec
+        Number.isFinite(configuredDurationSec) && configuredDurationSec > 0
+          ? configuredDurationSec
           : duration;
       const reverseMs = Math.max(reverseSeconds * 1000, 400);
-      const reverseRate = duration / reverseSeconds;
+      const reverseRate = reverseSeconds > 0 ? duration / reverseSeconds : 1;
       const startTime = performance.now();
       video.pause();
       video.currentTime = duration;
@@ -2415,7 +2468,7 @@ const ConstructorPage = ({ mode = 'constructor' }: ConstructorPageProps) => {
         video.currentTime = nextTime;
 
         if (elapsed >= reverseMs || nextTime <= 0.001) {
-          finishPreview();
+          finishPreview('reverse-complete');
           return;
         }
 
@@ -2425,30 +2478,145 @@ const ConstructorPage = ({ mode = 'constructor' }: ConstructorPageProps) => {
       reverseAnimationFrame.current = requestAnimationFrame(step);
     };
 
+    const attemptPlay = () => {
+      if (transitionPreview.reverseMode === 'reverse') return;
+      video
+        .play()
+        .catch((playError) => {
+          logTransitionIssue('play-failed', playError);
+        });
+    };
+
+    const loadSourceCandidate = async () => {
+      didStartPlayback = false;
+
+      if (startWatchdogTimer) {
+        clearTimeout(startWatchdogTimer);
+      }
+
+      try {
+        const playableSourceUrl = await resolvePlayableTransitionSource();
+        if (didFinish) return;
+
+        video.pause();
+        cleanupReverseFrame();
+        video.src = playableSourceUrl;
+        video.currentTime = 0;
+        video.load();
+
+        if (transitionPreview.reverseMode !== 'reverse') {
+          attemptPlay();
+        }
+
+        startWatchdogTimer = setTimeout(() => {
+          if (didStartPlayback || didFinish) return;
+          logTransitionIssue('playback-start-slow');
+          attemptPlay();
+        }, 12000);
+      } catch (error) {
+        logTransitionIssue('source-prepare-failed', error);
+        finishPreview('source-prepare-failed');
+      }
+    };
+
+    if (!sourceUrl) {
+      logTransitionIssue('missing-source');
+      finishPreview('missing-source');
+      return () => {
+        cleanupReverseFrame();
+      };
+    }
+
     const onLoadedMetadata = () => {
-      if (transitionPreview.reverseMode === 'reverse') {
+      if (didFinish) return;
+      if (transitionPreview.reverseMode === 'reverse' && !didStartPlayback) {
+        didStartPlayback = true;
+        if (startWatchdogTimer) {
+          clearTimeout(startWatchdogTimer);
+          startWatchdogTimer = null;
+        }
         runReversePreview();
         return;
       }
 
       video.currentTime = 0;
-      video.play().catch((playError) => {
-        console.error('Transition preview playback failed:', playError);
-        fallbackTimer = setTimeout(finishPreview, configuredDurationMs);
-      });
+      attemptPlay();
     };
 
-    const onEnded = () => finishPreview();
+    const onCanPlay = () => {
+      if (didFinish) return;
+      attemptPlay();
+    };
+
+    const onPlaying = () => {
+      if (didFinish) return;
+      didStartPlayback = true;
+      if (startWatchdogTimer) {
+        clearTimeout(startWatchdogTimer);
+        startWatchdogTimer = null;
+      }
+
+      if (transitionPreview.reverseMode !== 'reverse') {
+        const mediaDurationSec = Number(video.duration);
+        const durationSec =
+          Number.isFinite(configuredDurationSec) && configuredDurationSec > 0
+            ? configuredDurationSec
+            : Number.isFinite(mediaDurationSec) && mediaDurationSec > 0
+              ? mediaDurationSec
+              : NaN;
+        if (Number.isFinite(durationSec) && durationSec > 0) {
+          scheduleFinishByDuration(durationSec);
+        }
+      }
+    };
+
+    const onEnded = () => finishPreview('ended');
+
+    const onPlaybackError = (eventName: string, error?: unknown) => {
+      if (didFinish) return;
+      logTransitionIssue(eventName, error);
+      finishPreview(eventName);
+    };
+
+    const onError = () => onPlaybackError('video-error');
+    const onAbort = () => onPlaybackError('video-abort');
+    const onStalled = () => {
+      if (didFinish) return;
+      logTransitionIssue('video-stalled');
+    };
 
     video.addEventListener('loadedmetadata', onLoadedMetadata);
+    video.addEventListener('canplay', onCanPlay);
+    video.addEventListener('playing', onPlaying);
     video.addEventListener('ended', onEnded);
-    fallbackTimer = setTimeout(finishPreview, configuredDurationMs + 500);
+    video.addEventListener('error', onError);
+    video.addEventListener('abort', onAbort);
+    video.addEventListener('stalled', onStalled);
+
+    hardTimeoutTimer = setTimeout(() => {
+      if (didFinish) return;
+      logTransitionIssue('hard-timeout');
+      finishPreview('hard-timeout');
+    }, 45000);
+
+    void loadSourceCandidate();
 
     return () => {
       video.removeEventListener('loadedmetadata', onLoadedMetadata);
+      video.removeEventListener('canplay', onCanPlay);
+      video.removeEventListener('playing', onPlaying);
       video.removeEventListener('ended', onEnded);
+      video.removeEventListener('error', onError);
+      video.removeEventListener('abort', onAbort);
+      video.removeEventListener('stalled', onStalled);
+      clearTimers();
       cleanupReverseFrame();
-      if (fallbackTimer) clearTimeout(fallbackTimer);
+      cleanupPreviewBlobUrl();
+      if (!didFinish) {
+        video.pause();
+        video.removeAttribute('src');
+        video.load();
+      }
     };
   }, [transitionPreview]);
 
@@ -3668,42 +3836,15 @@ const ConstructorPage = ({ mode = 'constructor' }: ConstructorPageProps) => {
       </div>
 
       {transitionPreview && (
-        <div className='fixed inset-0 z-50 bg-black/95 flex items-center justify-center'>
+        <div className='fixed inset-0 z-50 overflow-hidden pointer-events-none'>
           <video
             ref={transitionVideoRef}
-            src={resolveAssetPlaybackUrl(
-              transitionPreview.reverseMode === 'separate'
-                ? transitionPreview.reverseVideoUrl || ''
-                : transitionPreview.videoUrl,
-            )}
-            className='h-full w-full object-cover'
+            className='absolute inset-0 h-full w-full object-cover transition-opacity duration-300 ease-linear'
             muted
             playsInline
-            autoPlay={transitionPreview.reverseMode !== 'reverse'}
             preload='auto'
+            disablePictureInPicture
           />
-          <div className='absolute bottom-4 left-4 text-xs text-white/80'>
-            {transitionPreview.title}
-          </div>
-          <button
-            type='button'
-            className='absolute top-4 right-4 rounded bg-white/20 px-3 py-1 text-xs text-white hover:bg-white/30'
-            onClick={() => {
-              setTransitionPreview(null);
-              setPendingNavigationPageId((pendingPageId) => {
-                const nextPageId = String(pendingPageId || '').trim();
-                if (nextPageId) {
-                  setActivePageId(nextPageId);
-                  setSelectedElementId('');
-                  setSelectedMenuItem('none');
-                  setErrorMessage('');
-                }
-                return '';
-              });
-            }}
-          >
-            Close
-          </button>
         </div>
       )}