如何在flutter中并排合并两个视频

dependencies:
  flutter:
    sdk: flutter
  video_player: ^2.2.5
  flutter_ffmpeg: ^0.4.0

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

class MergeVideosPage extends StatefulWidget {
  @override
  _MergeVideosPageState createState() => _MergeVideosPageState();
}

class _MergeVideosPageState extends State<MergeVideosPage> {
  VideoPlayerController _controller1;
  VideoPlayerController _controller2;

  @override
  void initState() {
    super.initState();
    _controller1 = VideoPlayerController.asset('assets/video1.mp4')
      ..initialize().then((_) {
        setState(() {});
      });
    _controller2 = VideoPlayerController.asset('assets/video2.mp4')
      ..initialize().then((_) {
        setState(() {});
      });
  }

  @override
  void dispose() {
    _controller1.dispose();
    _controller2.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Merge Videos'),
      ),
      body: Column(
        children: [
          _controller1.value.isInitialized
              ? AspectRatio(
                  aspectRatio: _controller1.value.aspectRatio,
                  child: VideoPlayer(_controller1),
                )
              : Container(),
          _controller2.value.isInitialized
              ? AspectRatio(
                  aspectRatio: _controller2.value.aspectRatio,
                  child: VideoPlayer(_controller2),
                )
              : Container(),
        ],
      ),
    );
  }
}

class _MergeVideosPageState extends State<MergeVideosPage> {
  // ...

  FlutterFFmpeg _flutterFFmpeg = FlutterFFmpeg();

  void _mergeVideos() async {
    final outputFilePath = '/path/to/output.mp4';

    final arguments = '-i /path/to/video1.mp4 -i /path/to/video2.mp4 -filter_complex hstack $outputFilePath';

    final result = await _flutterFFmpeg.execute(arguments);
    if (result == 0) {
      print('Videos merged successfully!');
    } else {
      print('Failed to merge videos. Error code: $result');
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      // ...
      floatingActionButton: FloatingActionButton(
        onPressed: _mergeVideos,
        child: Icon(Icons.merge_type),
      ),
    );
  }
}