参考资料：
    flutter - 使用flutter firebase_messaging插件发送通知声音
    https://www.coder.work/article/277913
    手把手带你写 Flutter 系统音量插件(Android\iOS)
    https://juejin.im/post/5dad1b9b5188250ec90be4cc
    FlutterでFCMを使ったプッシュ通知を実装してみた
    https://dev.classmethod.jp/articles/flutter_fcm_push1/
    Play and pause a video
    https://flutter.dev/docs/cookbook/plugins/play-video
    本地远程音频播放，支持多个同时播放
    https://pub.dev/packages/audioplayers
    https://pub.dev/packages/firebase_messaging#-readme-tab-
    https://pub.dev/packages/video_player