fix: use returncode is None instead of .done() for subprocess check

backend/app/utils/hls.py

@@ -10,10 +10,14 @@ logger = logging.getLogger(__name__)
 
 
 def _deltacast_device_exists(port_index: int) -> bool:
-    """Return True if the deltacast device node exists on the host."""
     return os.path.exists(f"/dev/deltacast{port_index}")
 
 
+def _proc_running(proc) -> bool:
+    """Return True if the subprocess is still alive."""
+    return proc is not None and proc.returncode is None
+
+
 class HLSPreviewManager:
     """
     Manages FFmpeg HLS transcoding processes for video preview.
@@ -26,13 +30,10 @@ class HLSPreviewManager:
         self._processes: dict[int, asyncio.subprocess.Process] = {}
 
     async def start_preview(self, port_index: int) -> None:
-        if port_index in self._processes and self._processes[port_index] is not None:
+        existing = self._processes.get(port_index)
-            proc = self._processes[port_index]
+        if _proc_running(existing):
-            if not proc.done():
+            logger.info(f"Port {port_index}: HLS preview already running")
-                logger.info(f"Port {port_index}: HLS preview already running")
+            return
-                return
-            # Process died — clean up and restart
-            self._processes.pop(port_index)
 
         self.hls_dir.mkdir(parents=True, exist_ok=True)
 
@@ -44,8 +45,6 @@ class HLSPreviewManager:
         else:
             logger.info(f"Port {port_index}: Starting HLS preview from deltacast{port_index}")
 
-        logger.debug(f"Port {port_index}: FFmpeg command: {' '.join(command)}")
-
         try:
             process = await asyncio.create_subprocess_exec(
                 *command,
@@ -60,10 +59,10 @@ class HLSPreviewManager:
             raise
 
     async def stop_preview(self, port_index: int) -> None:
-        if port_index not in self._processes or self._processes[port_index] is None:
+        process = self._processes.get(port_index)
+        if not _proc_running(process):
             return
 
-        process = self._processes[port_index]
         logger.info(f"Port {port_index}: Stopping HLS preview (PID: {process.pid})")
 
         try:
@@ -107,23 +106,18 @@ class HLSPreviewManager:
         return self.hls_dir / f"port_{port_index}.m3u8"
 
     def is_previewing(self, port_index: int) -> bool:
-        if port_index not in self._processes:
+        return _proc_running(self._processes.get(port_index))
-            return False
-        process = self._processes[port_index]
-        return process is not None and not process.done()
 
     def _build_hls_command(self, port_index: int, use_test_src: bool = False) -> list[str]:
         playlist_path = self.get_playlist_path(port_index)
 
         if use_test_src:
-            # lavfi test source: colour bars + timestamp overlay + tone
-            # Port number overlaid so each card is visually distinct
             command = [
                 self.settings.ffmpeg_path,
                 "-f", "lavfi",
                 "-i", (
                     f"testsrc2=size=1280x720:rate=30,"
-                    f"drawtext=text='SDI PORT {port_index} — NO SIGNAL':"
+                    f"drawtext=text='SDI PORT {port_index} \u2014 NO SIGNAL':"
                     f"fontsize=36:fontcolor=white:x=(w-text_w)/2:y=(h-text_h)/2,"
                     f"drawtext=text='%{{localtime\\:%H\\:%M\\:%S}}':"
                     f"fontsize=24:fontcolor=yellow:x=10:y=10"