diff --git a/app/static/public/js/video.js b/app/static/public/js/video.js
index 71748fa..c9987ca 100644
--- a/app/static/public/js/video.js
+++ b/app/static/public/js/video.js
@@ -1501,43 +1501,54 @@
       const segBSource = `${prefix}_b_source.mp4`;
       const segA = `${prefix}_a.mp4`;
       const segB = `${prefix}_b.mp4`;
+      const segANorm = `${prefix}_a_norm.mp4`;
+      const segBNorm = `${prefix}_b_norm.mp4`;
       const listFile = `${prefix}_list.txt`;
       const mergedFile = `${prefix}_merged.mp4`;
       try {
-      await ffmpegWriteFile(ff, segASource, sourceStable);
-      await ffmpegWriteFile(ff, segBSource, generatedBuffer);
-      const trimSeconds = (Math.max(0, lockedTimestampMs) / 1000).toFixed(3);
-      if (Number(trimSeconds) > 0) {
-        await ffmpegExec(
-          ff,
-          ['-y', '-i', segASource, '-t', trimSeconds, '-c:v', 'libx264', '-preset', 'ultrafast', '-pix_fmt', 'yuv420p', '-c:a', 'aac', '-ar', '48000', '-ac', '2', segA]
-        );
-        await ffmpegExec(
-          ff,
-          ['-y', '-i', segBSource, '-c:v', 'libx264', '-preset', 'ultrafast', '-pix_fmt', 'yuv420p', '-c:a', 'aac', '-ar', '48000', '-ac', '2', segB]
-        );
+        const trimSeconds = (Math.max(0, lockedTimestampMs) / 1000).toFixed(3);
+        if (Number(trimSeconds) <= 0) {
+          return new Blob([toStableUint8(generatedBuffer)], { type: 'video/mp4' });
+        }
+        await ffmpegWriteFile(ff, segASource, sourceStable);
+        await ffmpegWriteFile(ff, segBSource, generatedBuffer);
+
+        await ffmpegExec(ff, ['-y', '-i', segASource, '-t', trimSeconds, '-c', 'copy', segA]);
         await ffmpegWriteFile(
           ff,
           listFile,
-          new TextEncoder().encode(`file '${segA}'\nfile '${segB}'\n`)
+          new TextEncoder().encode(`file '${segA}'\nfile '${segBSource}'\n`)
         );
-        await ffmpegExec(
-          ff,
-          ['-y', '-f', 'concat', '-safe', '0', '-i', listFile, '-c:v', 'libx264', '-preset', 'ultrafast', '-pix_fmt', 'yuv420p', '-c:a', 'aac', '-ar', '48000', '-ac', '2', mergedFile]
-        );
-      } else {
-        await ffmpegExec(
-          ff,
-          ['-y', '-i', segBSource, '-c:v', 'libx264', '-preset', 'ultrafast', '-pix_fmt', 'yuv420p', '-c:a', 'aac', '-ar', '48000', '-ac', '2', mergedFile]
-        );
-      }
-      const merged = await ffmpegReadFile(ff, mergedFile);
-      return new Blob([toStableUint8(merged)], { type: 'video/mp4' });
+        try {
+          await ffmpegExec(ff, ['-y', '-f', 'concat', '-safe', '0', '-i', listFile, '-c', 'copy', mergedFile]);
+        } catch (copyErr) {
+          await ffmpegExec(
+            ff,
+            ['-y', '-i', segASource, '-t', trimSeconds, '-c:v', 'libx264', '-preset', 'ultrafast', '-pix_fmt', 'yuv420p', '-c:a', 'aac', '-ar', '48000', '-ac', '2', segANorm]
+          );
+          await ffmpegExec(
+            ff,
+            ['-y', '-i', segBSource, '-c:v', 'libx264', '-preset', 'ultrafast', '-pix_fmt', 'yuv420p', '-c:a', 'aac', '-ar', '48000', '-ac', '2', segBNorm]
+          );
+          await ffmpegWriteFile(
+            ff,
+            listFile,
+            new TextEncoder().encode(`file '${segANorm}'\nfile '${segBNorm}'\n`)
+          );
+          await ffmpegExec(
+            ff,
+            ['-y', '-f', 'concat', '-safe', '0', '-i', listFile, '-c:v', 'libx264', '-preset', 'ultrafast', '-pix_fmt', 'yuv420p', '-c:a', 'aac', '-ar', '48000', '-ac', '2', mergedFile]
+          );
+        }
+        const merged = await ffmpegReadFile(ff, mergedFile);
+        return new Blob([toStableUint8(merged)], { type: 'video/mp4' });
       } finally {
         await ffmpegDeleteFileSafe(ff, segASource);
         await ffmpegDeleteFileSafe(ff, segBSource);
         await ffmpegDeleteFileSafe(ff, segA);
         await ffmpegDeleteFileSafe(ff, segB);
+        await ffmpegDeleteFileSafe(ff, segANorm);
+        await ffmpegDeleteFileSafe(ff, segBNorm);
         await ffmpegDeleteFileSafe(ff, listFile);
         await ffmpegDeleteFileSafe(ff, mergedFile);
       }
diff --git a/app/static/public/pages/video.html b/app/static/public/pages/video.html
index 53ddeec..41a555c 100644
--- a/app/static/public/pages/video.html
+++ b/app/static/public/pages/video.html
@@ -274,7 +274,7 @@
   <script src="/static/common/js/pwa.js?v=0.1.1"></script>
   <script src="/static/vendor/ffmpeg/ffmpeg.js?v=0.1.0"></script>
   <script src="/static/vendor/ffmpeg/ffmpeg-util.js?v=0.1.0"></script>
-  <script src="/static/public/js/video.js?v=0.4.7"></script>
+  <script src="/static/public/js/video.js?v=0.4.8"></script>
 </body>
 
 </html>