Flutter如何保存(重新编码)视频上的文本覆盖

import 'package:flutter/material.dart';
import 'package:video_player/video_player.dart';

class VideoOverlay extends StatefulWidget {
  final String videoPath;

  VideoOverlay({required this.videoPath});

  @override
  _VideoOverlayState createState() => _VideoOverlayState();
}

class _VideoOverlayState extends State<VideoOverlay> {
  late VideoPlayerController _controller;
  late TextEditingController _textController;
  late GlobalKey _textKey;

  @override
  void initState() {
    super.initState();
    _controller = VideoPlayerController.asset(widget.videoPath)
      ..initialize().then((_) {
        setState(() {});
      });
    _textController = TextEditingController();
    _textKey = GlobalKey();
  }

  @override
  void dispose() {
    _controller.dispose();
    _textController.dispose();
    super.dispose();
  }

  void _saveVideo() async {
    RenderRepaintBoundary boundary =
        _textKey.currentContext!.findRenderObject() as RenderRepaintBoundary;
    ui.Image image = await boundary.toImage();
    ByteData? byteData =
        await image.toByteData(format: ui.ImageByteFormat.png);
    Uint8List pngBytes = byteData!.buffer.asUint8List();

    final Directory extDir = await getApplicationDocumentsDirectory();
    final String dirPath = '${extDir.path}/Videos';
    await Directory(dirPath).create(recursive: true);
    final String filePath = '$dirPath/${DateTime.now().millisecondsSinceEpoch}.mp4';

    await _controller.saveToFile(filePath, textOverlay: pngBytes);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Video Overlay'),
      ),
      body: _controller.value.isInitialized
          ? Stack(
              children: [
                AspectRatio(
                  aspectRatio: _controller.value.aspectRatio,
                  child: VideoPlayer(_controller),
                ),
                RepaintBoundary(
                  key: _textKey,
                  child: TextField(
                    controller: _textController,
                    decoration: InputDecoration(
                      labelText: 'Enter text',
                    ),
                  ),
                ),
              ],
            )
          : Container(),
      floatingActionButton: FloatingActionButton(
        onPressed: _saveVideo,
        child: Icon(Icons.save),
      ),
    );
  }
}