Improve YouTube download with better error handling and auth

app.py

@@ -280,13 +280,29 @@ def download_youtube(url: str) -> tuple:
                 'preferredcodec': 'wav',
             }],
             'quiet': True,
+            'no_warnings': True,
+            'socket_timeout': 60,
+            'retries': 5,
+            'extractor_args': {
+                'youtube': {
+                    'player_client': ['web', 'android', 'ios'],
+                }
+            },
         }
+
+        # Try with browser cookies on local, skip on HF Space
+        if not IS_HF_SPACE:
+            ydl_opts['cookiesfrombrowser'] = ('chrome',)
+
         with yt_dlp.YoutubeDL(ydl_opts) as ydl:
             info = ydl.extract_info(url, download=True)
             title = info.get('title', 'Unknown')
         return str(output_path), title
     except Exception as e:
-        return None, str(e)
+        error_msg = str(e)
+        if 'Sign in to confirm' in error_msg or 'bot' in error_msg.lower():
+            return None, "YouTube requires authentication. Please upload the audio file directly instead, or try a different video."
+        return None, error_msg
 
 @spaces.GPU(duration=120)
 def separate_stems(audio_path: str, progress=None) -> dict: