fix: Windows Playwright HTML rendering under Streamlit

Streamlit/Tornado switches the asyncio policy to WindowsSelectorEventLoopPolicy on Windows, which breaks Playwright subprocess creation. Fixed by using an explicit ProactorEventLoop on Windows, and tracking the event loop per browser instance to detect cross-loop reuse.

pixelle_video/services/frame_html.py

@@ -25,6 +25,7 @@ Linux Environment Requirements:
     Playwright browser install: playwright install --with-deps chromium
 """
 
+import asyncio
 import os
 import re
 import tempfile
@@ -55,6 +56,7 @@ class HTMLFrameGenerator:
     
     _browser = None
     _playwright = None
+    _browser_loop = None
 
     def __init__(self, template_path: str):
         """
@@ -307,7 +309,22 @@ class HTMLFrameGenerator:
     @classmethod
     async def _ensure_browser(cls):
         """Lazily initialize a shared Playwright browser instance"""
-        if cls._browser is None or not cls._browser.is_connected():
+        current_loop = asyncio.get_running_loop()
+        browser_usable = (
+            cls._browser is not None
+            and cls._browser_loop is current_loop
+            and cls._browser.is_connected()
+        )
+
+        if not browser_usable:
+            if cls._browser is not None and cls._browser_loop is not current_loop:
+                logger.warning(
+                    "Detected cross-loop Playwright browser reuse attempt; "
+                    "recreating browser for current event loop"
+                )
+
+            cls._browser = None
+            cls._playwright = None
             from playwright.async_api import async_playwright
             cls._playwright = await async_playwright().start()
             cls._browser = await cls._playwright.chromium.launch(
@@ -318,6 +335,7 @@ class HTMLFrameGenerator:
                     '--disable-extensions',
                 ]
             )
+            cls._browser_loop = current_loop
             logger.debug("Initialized Playwright Chromium browser")
         return cls._browser
 
@@ -327,6 +345,7 @@ class HTMLFrameGenerator:
         if cls._browser:
             await cls._browser.close()
             cls._browser = None
+            cls._browser_loop = None
         if cls._playwright:
             await cls._playwright.stop()
             cls._playwright = None
@@ -410,5 +429,7 @@ class HTMLFrameGenerator:
             return output_path
             
         except Exception as e:
-            logger.error(f"Failed to render HTML template: {e}")
+            logger.exception("Failed to render HTML template")
-            raise RuntimeError(f"HTML rendering failed: {e}")
+            raise RuntimeError(
+                f"HTML rendering failed: {type(e).__name__}: {e}"
+            ) from e

web/utils/async_helpers.py

@@ -15,6 +15,7 @@ Async helper functions for web UI
 """
 
 import asyncio
+import sys
 import tomllib
 from pathlib import Path
 
@@ -23,6 +24,23 @@ from loguru import logger
 
 def run_async(coro):
     """Run async coroutine in sync context"""
+    if sys.platform == "win32":
+        # Streamlit/Tornado may switch the global asyncio policy to
+        # WindowsSelectorEventLoopPolicy, which breaks subprocess-based
+        # libraries such as Playwright on Windows. Use an explicit
+        # Proactor loop here so this sync bridge does not depend on the
+        # ambient global policy.
+        loop = asyncio.ProactorEventLoop()
+        try:
+            return loop.run_until_complete(coro)
+        finally:
+            try:
+                from pixelle_video.services.frame_html import HTMLFrameGenerator
+
+                loop.run_until_complete(HTMLFrameGenerator.close_browser())
+            except Exception as e:
+                logger.debug(f"Failed to cleanup HTML frame browser before loop close: {e}")
+            loop.close()
     return asyncio.run(coro)