我正在制作一个Flutter视频下载管理器。我正在使用flutter_downloader插件。但所面临的问题是，要么视频不下载，要么下载后不播放。下面是从Facebook和Instagram下载视频的代码。

Future<void> _startDownload() async {
    final url = _urlController.text.trim();
    if (url.isEmpty) {
      showDialog(
        context: context,
        builder: (context) => AlertDialog(
          title: const Text('Empty URL'),
          content: const Text('Please enter a video URL.'),
          actions: [
            TextButton(
              onPressed: () => Navigator.pop(context),
              child: const Text('OK'),
            ),
          ],
        ),
      );
      return;
    } else if (!isValidVideoUrl(url)) {
      // Show an error message or handle the invalid URL case
      showDialog(
        context: context,
        builder: (context) => AlertDialog(
          title: const Text('Invalid URL'),
          content: const Text('Please enter a valid video URL.'),
          actions: [
            TextButton(
              onPressed: () => Navigator.pop(context),
              child: const Text('OK'),
            ),
          ],
        ),
      );
      return;
    } else {
      TaskInfo task = TaskInfo(url: url);
      await _requestDownload(task);
      setState(() {
        _tasks!.add(task);
        _items!.add(ItemHolder(name: task.name, task: task));
      });
    }
  }
bool isValidVideoUrl(String url) {
    final Uri? uri = Uri.tryParse(url);

    if (uri == null) {
      // Invalid URL format
      return false;
    }

    // Check if the URL scheme is HTTP or HTTPS
    if (uri.scheme != 'http' && uri.scheme != 'https') {
      return false;
    }

    // Check if the URL host belongs to a valid video hosting platform
    final String host = uri.host.toLowerCase();
    if (host.contains('www.instagram.com') ||
        host.contains('www.tiktok.com') ||
        host.contains('www.reels.com') ||
        host.contains('www.facebook.com')) {
      return true;
    }

    //Invalid video URL
    return false;
  }

解析URI

Future<void> _requestDownload(TaskInfo task) async {
    final url = task.url!;
    if (_permissionReady) {
      final fileName = '${DateTime.now().millisecondsSinceEpoch}.mp4';

      final response = await Dio().head(url);
      final contentType = response.headers['content-type']?.toString();
      final fileExtension = _getFileExtension(contentType);

      task.taskId = await FlutterDownloader.enqueue(
        url: url,
        savedDir: _localPath!,
        fileName: '$fileName$fileExtension',
        saveInPublicStorage: _saveInPublicStorage,
        showNotification: true,
        openFileFromNotification: true,
      );
    }
  }

  String _getFileExtension(String? contentType) {
    if (contentType != null) {
      if (contentType.contains('video/mp4')) {
        return '.mp4';
      } else if (contentType.contains('video/3gpp')) {
        return '.3gp';
      } else if (contentType.contains('video/mpeg')) {
        return '.mpg';
      }
      // Add more cases for other content types and their corresponding file extensions
    }
    return '.mp4'; // Default to '.mp4' if the content type is unknown
  }

我想以正确的格式下载文件，下载后必须播放视频。