how to convert audio url into a file in flutter web?

I am using microphone package to record voice, Flutter stores audio for a while we can play as Audio url that but i need to store the voice url in form of file in firebase storage. heare my code....

    void handleAudioState(AudioState state) {
        setState(() {
          if (audioState == AudioState.not) {
        // Starts recording
           try{
             _recorder.start();
             audioState = AudioState.recording;
       }
          catch(e){
           print(e.toString());
       }
        // Finished recording
      } 
         else if (audioState == AudioState.recording) {
         audioState = AudioState.play;
         _recorder.stop();
        // Play recorded audio
      } 
         else if (audioState == AudioState.play) {
         audioState = AudioState.stop;
         dynamic rec=_recorder.toBytes();
         print(rec.toString());
         // var file= File.fromRawPath(rec);
         //print(file);
         _audioPlayer=AudioPlayer();
         _audioPlayer.setUrl(_recorder.value.recording!.url).then((value){
          print(_recorder.value.recording!.url);
          return _audioPlayer.play().then((value){
            setState(() {
              audioState = AudioState.play;
            });
          });
        });
        // Stop recorded audio
      } else if (audioState == AudioState.stop) {
        audioState = AudioState.play;
        _audioPlayer.stop();
      }
    });
  }

 void handleAudioState(AudioState state) {
    setState(() {
      if (audioState == AudioState.not) {
        // Starts recording
       try{
         _recorder.start();
         audioState = AudioState.recording;
       }
       catch(e){
         print(e.toString());
       }
        // Finished recording
      } else if (audioState == AudioState.recording) {
        audioState = AudioState.play;
        _recorder.stop();
        // Play recorded audio
      } else if (audioState == AudioState.play) {
        audioState = AudioState.stop;
        dynamic rec=_recorder.toBytes();
        print(rec.toString());
       // var file= File.fromRawPath(rec);
       //print(file);
        _audioPlayer=AudioPlayer();
        _audioPlayer.setUrl(_recorder.value.recording!.url).then((value){
          print(_recorder.value.recording!.url);
          return _audioPlayer.play().then((value){
            setState(() {
              audioState = AudioState.play;
            });
          });
        });
        // Stop recorded audio
      } else if (audioState == AudioState.stop) {
        audioState = AudioState.play;
        _audioPlayer.stop();
      }
    });
  }

i am using below Packages just_audio: ^0.8.0 microphone: please let me know how to do this , thanks in anticipation