diff --git a/viewer/media_player.py b/viewer/media_player.py
index fba2db9e0..a9720a6a8 100644
--- a/viewer/media_player.py
+++ b/viewer/media_player.py
@@ -57,6 +57,44 @@ def is_playing(self):
         return False
 
 
+def _detect_hdmi_audio_device():
+    """Auto-detect connected HDMI audio device on Pi4/Pi5.
+
+    Pi4 has two HDMI ports:
+      - HDMI-A-1 = card 1 = vc4hdmi0
+      - HDMI-A-2 = card 2 = vc4hdmi1
+
+    Checks /sys/class/drm/cardN-HDMI-A-N/status to find
+    which port is connected and returns the matching ALSA device.
+    Uses sysdefault instead of default for reliable audio output.
+    """
+    import os
+
+    for port, card_name in [
+        ('card1-HDMI-A-1', 'vc4hdmi0'),
+        ('card1-HDMI-A-2', 'vc4hdmi1'),
+    ]:
+        status_path = f'/sys/class/drm/{port}/status'
+        try:
+            if os.path.exists(status_path):
+                with open(status_path) as f:
+                    if f.read().strip() == 'connected':
+                        logging.info(
+                            'Detected connected HDMI: %s -> '
+                            'sysdefault:CARD=%s',
+                            port,
+                            card_name,
+                        )
+                        return f'sysdefault:CARD={card_name}'
+        except OSError:
+            pass
+
+    logging.warning(
+        'No connected HDMI detected, falling back to sysdefault:CARD=vc4hdmi0',
+    )
+    return 'sysdefault:CARD=vc4hdmi0'
+
+
 class VLCMediaPlayer(MediaPlayer):
     def __init__(self):
         MediaPlayer.__init__(self)
@@ -70,16 +108,16 @@ def __init__(self):
     def get_alsa_audio_device(self):
         if settings['audio_output'] == 'local':
             if get_device_type() == 'pi5':
-                return 'default:CARD=vc4hdmi0'
+                return 'sysdefault:CARD=vc4hdmi0'
 
             return 'plughw:CARD=Headphones'
         else:
             if get_device_type() in ['pi4', 'pi5']:
-                return 'default:CARD=vc4hdmi0'
+                return _detect_hdmi_audio_device()
             elif get_device_type() in ['pi1', 'pi2', 'pi3']:
-                return 'default:CARD=vc4hdmi'
+                return 'sysdefault:CARD=vc4hdmi'
             else:
-                return 'default:CARD=HID'
+                return 'sysdefault:CARD=HID'
 
     def __get_options(self):
         return [