我正在学习使用google_speech ^2.2.0 API的medical_dictation模型构建flutter-firebase应用程序，用于语音到文本。我已经在GCP上创建了一个服务帐户，启用了语音转文本API，并保存了API密钥。我已经将API密钥保存在flutter项目的根文件夹下为'assets/test_service_account.json'，并将音频文件保存为'assets/audio/test.wav'。我还在pubspec.yaml文件中添加了路径。但我得到了这个例外：
无法加载模块：Public到这里去看看！“assets/service_account_key.json”。资产不存在或数据为空。）
类似的例外我得到关于'test.wav'。
这是我的代码。

import 'package:flutter/services.dart' show rootBundle;
import 'package:google_speech/google_speech.dart' as gs;
import 'package:flutter/material.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:google_speech/speech_client_authenticator.dart';

String audioFilePath = 'assets/audio/test.wav';

Future<String> transcribeAudio(String audioFilePath) async {
  final serviceAccountData =
      await rootBundle.loadString('assets/service_account_key.json');
  final serviceAccount = ServiceAccount.fromString(serviceAccountData);

  final data = await rootBundle.load('assets/audio/test.wav');
  final audio = data.buffer.asUint8List();

  final config = gs.RecognitionConfig(
    encoding: gs.AudioEncoding.LINEAR16,
    model: gs.RecognitionModel.medical_dictation,
    enableAutomaticPunctuation: true,
    sampleRateHertz: 16000,
    languageCode: 'en-US',
  );

  final speechToText = gs.SpeechToText.viaServiceAccount(serviceAccount);

  final response = await speechToText.recognize(config, audio);
  final transcript = response.results
      .map((result) => result.alternatives.first.transcript)
      .join(' ');

  return transcript;
}

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();

  String transcript = await transcribeAudio(audioFilePath);
  print('Transcript: $transcript');
}