Use state machine for syncing playback

desktop-client/main.py

@@ -105,8 +105,8 @@ class VlcSyncApp(QMainWindow):
         self.local_file_path = None
         self.lobby_widget.clear_file()
 
-    def _on_room_sync_action(self, action, position_s):
+    def _on_room_sync_action(self, action, position_s, req_id):
-        self.sync_client.send_message({"type": "sync", "action": action, "position": position_s})
+        self.sync_client.send_message({"type": "sync", "action": action, "position": position_s, "req_id": req_id})
         
     def _on_room_chat(self, text):
         self.sync_client.send_message({"type": "chat", "message": text})

desktop-client/room_widget.py

@@ -6,12 +6,20 @@ from PyQt6.QtWidgets import (
 )
 from PyQt6.QtCore import Qt, pyqtSignal, QTimer
 from PyQt6.QtGui import QIcon
+import uuid
 
 from vlc_player import VLCSyncPlayer
 
+class ExpectedVlcEvent:
+    def __init__(self, action: str, req_id: str, target_val=None):
+        self.action = action
+        self.req_id = req_id
+        self.target_val = target_val
+        self.timestamp = datetime.datetime.now()
+
 class RoomWidget(QWidget):
     leave_requested = pyqtSignal()
-    sync_action_requested = pyqtSignal(str, float)  # action, position_s
+    sync_action_requested = pyqtSignal(str, float, str)  # action, position_s, req_id
     chat_message_ready = pyqtSignal(str)          # raw message text
     
     def __init__(self):
@@ -19,7 +27,7 @@ class RoomWidget(QWidget):
         
         self.username = ""
         self.room_code = ""
-        self.ignore_vlc_events = False
+        self.expected_vlc_events = []
         self.last_reported_time_ms = 0
         
         self._setup_ui()
@@ -210,16 +218,38 @@ class RoomWidget(QWidget):
                 toast.deleteLater()
             QTimer.singleShot(1500, reset)
 
+    def _tell_vlc_and_expect(self, action: str, position_s: float):
+        req_id = str(uuid.uuid4())[:8]
+        target_ms = int(position_s * 1000)
+        
+        # Clean up old expectations (e.g. VLC dropped the event or we missed it)
+        now = datetime.datetime.now()
+        self.expected_vlc_events = [e for e in self.expected_vlc_events 
+                                  if (now - e.timestamp).total_seconds() < 3.0]
+        
+        self.expected_vlc_events.append(ExpectedVlcEvent(action, req_id, target_ms))
+        
+        if action == "play":
+            self.vlc_player.seek(target_ms)
+            self.vlc_player.play()
+            self.play_btn.setText("⏸")
+        elif action == "pause":
+            self.vlc_player.seek(target_ms)
+            self.vlc_player.pause()
+            self.play_btn.setText("▶")
+        elif action == "seek":
+            self.vlc_player.seek(target_ms)
+            
+        return req_id
+            
     def toggle_playback(self):
         position_s = self.vlc_player.current_time_ms / 1000.0
         if self.vlc_player.is_playing:
-            self.vlc_player.pause()
+            req = self._tell_vlc_and_expect("pause", position_s)
-            self.play_btn.setText("▶")
+            self.sync_action_requested.emit("pause", position_s, req)
-            self.sync_action_requested.emit("pause", position_s)
         else:
-            self.vlc_player.play()
+            req = self._tell_vlc_and_expect("play", position_s)
-            self.play_btn.setText("⏸")
+            self.sync_action_requested.emit("play", position_s, req)
-            self.sync_action_requested.emit("play", position_s)
             
     def on_vlc_time(self, time_ms: int):
         length_ms = self.vlc_player.get_length()
@@ -235,17 +265,39 @@ class RoomWidget(QWidget):
                 self.seekbar.setValue(progress)
                 self.seekbar.blockSignals(False)
             
-        if self.last_reported_time_ms is not None:
+            if self.last_reported_time_ms is not None:
-            diff = abs(time_ms - self.last_reported_time_ms)
+                diff = abs(time_ms - self.last_reported_time_ms)
-            if diff > 2500 and not self.ignore_vlc_events:
+                
-                self.sync_action_requested.emit("seek", time_ms / 1000.0)
+                if diff > 1500:
-        self.last_reported_time_ms = time_ms
+                    # Look for a pending seek expectation
+                    matched = False
+                    for i, expected in enumerate(self.expected_vlc_events):
+                        if expected.action == "seek" and (expected.target_val is None or abs(expected.target_val - time_ms) < 2000):
+                            matched = True
+                            self.expected_vlc_events.pop(i)
+                            break
+                    
+                    if not matched:
+                        # Genuine user scrub!
+                        req = str(uuid.uuid4())[:8]
+                        self.sync_action_requested.emit("seek", time_ms / 1000.0, req)
+                        
+            self.last_reported_time_ms = time_ms
             
     def on_vlc_state(self, playing: bool, time_ms: int):
-        if self.ignore_vlc_events:
-            return
         action = "play" if playing else "pause"
-        self.sync_action_requested.emit(action, time_ms / 1000.0)
+        
+        # Look for a pending state change expectation
+        matched = False
+        for i, expected in enumerate(self.expected_vlc_events):
+            if expected.action == action:
+                matched = True
+                self.expected_vlc_events.pop(i)
+                break
+                
+        if not matched:
+            req = str(uuid.uuid4())[:8]
+            self.sync_action_requested.emit(action, time_ms / 1000.0, req)
 
     def on_seekbar_dragged(self, value):
         length_ms = self.vlc_player.get_length()
@@ -260,38 +312,23 @@ class RoomWidget(QWidget):
         length_ms = self.vlc_player.get_length()
         if length_ms > 0:
             target_ms = int((self.seekbar.value() / 1000.0) * length_ms)
-            self.vlc_player.seek(target_ms)
+            req = self._tell_vlc_and_expect("seek", target_ms / 1000.0)
-            self.sync_action_requested.emit("seek", target_ms / 1000.0)
+            self.sync_action_requested.emit("seek", target_ms / 1000.0, req)
 
     def on_volume_changed(self, value):
         self.vlc_player.set_volume(value)
 
     # --- Incoming Sync Logic ---
     def handle_sync_event(self, msg: dict):
-        self.ignore_vlc_events = True
-        
         action = msg.get("action")
         if not action:
             if msg.get("playing", False): action = "play"
             elif msg.get("playing") is False: action = "pause"
                 
         position_s = msg.get("position", 0)
-        position_ms = int(position_s * 1000)
         
-        if action == "play":
+        if action in ["play", "pause", "seek"]:
-            self.vlc_player.seek(position_ms)
+            self._tell_vlc_and_expect(action, position_s)
-            self.vlc_player.play()
-            self.play_btn.setText("⏸")
-        elif action == "pause":
-            self.vlc_player.seek(position_ms)
-            self.vlc_player.pause()
-            self.play_btn.setText("▶")
-        elif action == "seek":
-            self.vlc_player.seek(position_ms)
-            
-        def clear_ignore():
-            self.ignore_vlc_events = False
-        QTimer.singleShot(1500, clear_ignore)
         
         username = msg.get("username")
         if username and username != self.username:
@@ -385,8 +422,8 @@ class RoomWidget(QWidget):
                 else: target_ms = float(arg) * 1000
                 
             target_ms = max(0, min(target_ms, length_ms))
-            self.vlc_player.seek(int(target_ms))
+            req = self._tell_vlc_and_expect("seek", target_ms / 1000.0)
-            self.sync_action_requested.emit("seek", target_ms / 1000.0)
+            self.sync_action_requested.emit("seek", target_ms / 1000.0, req)
             return True
         except ValueError:
             return False