Add NVIDIA support for FFmpeg in Docker and enhance chat rendering functionality

- Introduced a new docker-compose.nvidia.yml for NVIDIA GPU support.
- Updated dockerstart.bat to allow optional NVIDIA runtime.
- Enhanced ContentDownloader to manage chat rendering status and font settings.
- Improved hardware acceleration detection in utils.py.
- Added tests for hardware acceleration and chat rendering behavior.

Co-authored-by: Copilot <copilot@github.com>

test_twitch_archive_simple.py

@@ -31,7 +31,7 @@ sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
 from modules.constants import DEFAULT_CONFIG
 from modules.file_manager import FileManager
 from modules.downloader import ContentDownloader
-from modules.utils import get_ffmpeg_executable, get_twitch_downloader_executable
+from modules.utils import get_ffmpeg_executable, get_twitch_downloader_executable, detect_hardware_acceleration, resolve_hwaccel_type
 
 
 def load_twitch_archive_module():
@@ -541,6 +541,69 @@ class TestLinuxToolResolution(unittest.TestCase):
 
         self.assertEqual(get_twitch_downloader_executable('linux'), '/usr/local/bin/TwitchDownloaderCLI')
 
+    @patch('modules.utils.os.path.exists', return_value=False)
+    @patch('modules.utils.shutil.which', return_value=None)
+    def test_linux_auto_hwaccel_falls_back_to_software_without_runtime(self, _mock_which, _mock_exists):
+        detected = detect_hardware_acceleration('auto', 'linux')
+
+        self.assertEqual(detected, 'none')
+        self.assertEqual(resolve_hwaccel_type(detected, 'linux'), 'none')
+
+    @patch('modules.utils.shutil.which', return_value='/usr/bin/nvidia-smi')
+    def test_linux_auto_hwaccel_uses_nvenc_when_nvidia_runtime_visible(self, _mock_which):
+        detected = detect_hardware_acceleration('auto', 'linux')
+
+        self.assertEqual(detected, 'nvenc')
+
+
+class TestChatRenderBehavior(unittest.TestCase):
+    """Regression tests for chat rendering defaults and retry behavior."""
+
+    @patch('modules.downloader.sys.platform', 'linux')
+    @patch('modules.downloader.subprocess.Popen')
+    def test_linux_chat_render_uses_container_safe_font(self, mock_popen):
+        with tempfile.TemporaryDirectory() as temp_dir:
+            json_path = os.path.join(temp_dir, 'chat.json')
+            video_path = os.path.join(temp_dir, 'chat.mp4')
+
+            with open(json_path, 'w', encoding='utf-8') as handle:
+                json.dump(
+                    {
+                        'comments': [
+                            {
+                                'message': {'body': 'hello world ' * 20},
+                                'commenter': {'display_name': 'tester'}
+                            }
+                        ]
+                    },
+                    handle
+                )
+
+            class FakeProcess:
+                def __init__(self, output_path: str):
+                    self.stdout = iter(['rendering'])
+                    self.output_path = output_path
+
+                def wait(self):
+                    with open(self.output_path, 'wb') as handle:
+                        handle.write(b'x' * 2048)
+                    return 0
+
+            captured = {}
+
+            def build_process(cmd, **_kwargs):
+                captured['cmd'] = cmd
+                return FakeProcess(video_path)
+
+            mock_popen.side_effect = build_process
+
+            downloader = ContentDownloader('TwitchDownloaderCLI', 'ffmpeg', {'downloadCHAT': True})
+
+            result = downloader.render_chat(json_path, video_path, '-c:v libx264 "{save_path}"')
+
+            self.assertTrue(result)
+            self.assertIn('DejaVu Sans', captured['cmd'])
+
 
 class TestMultiStreamerCleanupRegression(unittest.TestCase):
     """Regression tests for multi-streamer conversion and cleanup behavior."""
@@ -636,6 +699,59 @@ class TestMultiStreamerCleanupRegression(unittest.TestCase):
             upload_filename_base = archiver.file_manager.upload_to_cloud.call_args.args[0]
             self.assertFalse(upload_filename_base.startswith('LIVE_'))
 
+    def test_process_stream_preserves_files_when_chat_render_fails(self):
+        manager = self.module.TwitchArchiveManager(specific_streamer='maddoscientist0')
+
+        with tempfile.TemporaryDirectory() as temp_dir:
+            archiver = self._build_archiver(temp_dir)
+            archiver.downloadCHAT = True
+            archiver.downloadVOD = True
+            archiver.vodTimeout = 30
+            archiver.processor.process_raw_stream.return_value = True
+            archiver.file_manager.upload_to_cloud.return_value = True
+            archiver.downloader.last_chat_render_attempted = False
+            archiver.downloader.last_chat_render_succeeded = False
+
+            def write_raw_file(_stream_info, raw_path):
+                with open(raw_path, 'wb') as handle:
+                    handle.write(b'x' * 4096)
+                return True
+
+            def failed_chat_render(*_args, **_kwargs):
+                archiver.downloader.last_chat_render_attempted = True
+                archiver.downloader.last_chat_render_succeeded = False
+                return False
+
+            archiver.recorder.record.side_effect = write_raw_file
+            archiver.downloader.download_and_render_chat.side_effect = failed_chat_render
+            archiver.stream_monitor.get_latest_vod.return_value = {
+                'data': {
+                    'user': {
+                        'videos': {
+                            'edges': [
+                                {
+                                    'node': {
+                                        'id': '2756589076',
+                                        'title': 'Test',
+                                        'recordedAt': '2026-04-25T09:14:01Z'
+                                    }
+                                }
+                            ]
+                        }
+                    }
+                }
+            }
+
+            stream_info = {
+                'title': 'Test',
+                'createdAt': '2026-04-25T09:14:01Z'
+            }
+
+            manager._process_stream(archiver, stream_info, 'stream-id')
+
+            archiver.file_manager.clean_raw_file.assert_not_called()
+            archiver.file_manager.delete_local_files.assert_not_called()
+
 
 if __name__ == '__main__':
     # Run tests with verbose output