trying to fix export issue and waveform load

frontend/src/components/ExportDialog.tsx

@@ -16,6 +16,7 @@ export default function ExportDialog() {
     enhanceAudio: false,
     captions: 'none',
   });
+  const [exportError, setExportError] = useState<string | null>(null);
 
   const handleExport = useCallback(async () => {
     if (!videoPath) return;
@@ -31,6 +32,7 @@ export default function ExportDialog() {
     if (!outputPath) return;
 
     setExporting(true, 0);
+    setExportError(null);
     try {
       const keepSegments = getKeepSegments();
 
@@ -58,10 +60,20 @@ export default function ExportDialog() {
           ...options,
         }),
       });
-      if (!res.ok) throw new Error(`Export failed: ${res.statusText}`);
+      if (!res.ok) {
+        let detail = res.statusText;
+        try {
+          const body = await res.json();
+          if (body?.detail) detail = String(body.detail);
+        } catch {
+          // Keep statusText fallback when response body is not JSON.
+        }
+        throw new Error(`Export failed: ${detail}`);
+      }
       setExporting(false, 100);
     } catch (err) {
       console.error('Export error:', err);
+      setExportError(err instanceof Error ? err.message : 'Export failed');
       setExporting(false);
     }
   }, [videoPath, options, backendUrl, setExporting, getKeepSegments, cutRanges, muteRanges, gainRanges, speedRanges, globalGainDb, words]);
@@ -159,6 +171,12 @@ export default function ExportDialog() {
         )}
       </button>
 
+      {exportError && (
+        <div className="rounded border border-red-500/40 bg-red-500/10 px-3 py-2 text-xs text-red-300">
+          {exportError}
+        </div>
+      )}
+
       {options.mode === 'fast' && !hasCuts && (
         <p className="text-[10px] text-editor-text-muted text-center">
           Fast mode uses stream copy &mdash; no quality loss, exports in seconds.

frontend/src/components/WaveformTimeline.tsx

@@ -354,7 +354,11 @@ export default function WaveformTimeline({
           encodedPath: encodeURIComponent(videoPath ?? ''),
         });
         const waveformUrl2 = `${backendUrl}/audio/waveform?path=${encodeURIComponent(videoPath ?? '')}`;
-        setAudioError(`Waveform unavailable — ${err instanceof Error ? err.message : 'audio could not be decoded'} [URL: ${waveformUrl2}]`);
+        const errMessage = err instanceof Error ? err.message : 'audio could not be decoded';
+        const userMessage = errMessage === 'Load failed'
+          ? `Cannot reach backend at ${backendUrl}. Start the backend server and reload the project.`
+          : errMessage;
+        setAudioError(`Waveform unavailable — ${userMessage} [URL: ${waveformUrl2}]`);
       }
     };