如何为flutter中的chewie播放器添加视频选角？

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

class ChewiePlayerScreen extends StatefulWidget {
  @override
  _ChewiePlayerScreenState createState() => _ChewiePlayerScreenState();
}

class _ChewiePlayerScreenState extends State<ChewiePlayerScreen> {
  VideoPlayerController _videoPlayerController;
  ChewieController _chewieController;

  @override
  void initState() {
    super.initState();
    _videoPlayerController = VideoPlayerController.asset("your_video_path");
    _chewieController = ChewieController(
      videoPlayerController: _videoPlayerController,
      autoInitialize: true,
      placeholder: Container(
        color: Colors.grey,
      ),
      overlay: Container(
        alignment: Alignment.center,
        child: RaisedButton(
          child: Text("Select Character"),
          onPressed: () {
            _selectCharacter();
          },
        ),
      ),
    );
  }

  @override
  void dispose() {
    _videoPlayerController.dispose();
    _chewieController.dispose();
    super.dispose();
  }

  void _selectCharacter() async {
    var videoFile = await ImagePicker.pickVideo(source: ImageSource.gallery);
    if (videoFile != null) {
      setState(() {
        _videoPlayerController = VideoPlayerController.file(videoFile);
        _chewieController = ChewieController(
          videoPlayerController: _videoPlayerController,
          autoInitialize: true,
          placeholder: Container(
            color: Colors.grey,
          ),
          overlay: Container(
            alignment: Alignment.center,
            child: RaisedButton(
              child: Text("Select Character"),
              onPressed: () {
                _selectCharacter();
              },
            ),
          ),
        );
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Chewie Player"),
      ),
      body: Center(
        child: Chewie(
          controller: _chewieController,
        ),
      ),
    );
  }
}