I would like to realize this.

1. A user speaks to a web browser.
2. A web browser (Google Chrome) record user's voice as WAV file(Recorder.js) and send it to a python-flask server.

I realized this with the help of addpipe's simple recorder.js sample.
<https://github.com/addpipe/simple-recorderjs-demo>

This sample uses php server, so I changed the original app.js.

original app.js

```
xhr.open("POST","uplod.php",true);

```

my app.js

```
xhr.open("POST","/",true);

```

I checked my web app locally, then everything looked perfect. I use Windows 10, WSL, Debian 10/buster, python3.7.6, Google Chrome. Here is Terminal's record.

```
127.0.0.1 - - [03/Feb/2020 11:53:17] "GET / HTTP/1.1" 200 -
./file.wav exists
127.0.0.1 - - [03/Feb/2020 11:53:32] "POST / HTTP/1.1" 200 -

```

However, when I checked uploaded "file.wav" with ffprobe command, it was broken.

```
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100
file.wav: Invalid data found when processing input

```

This is screenshot of my app. When I push "save to disk" button, I can download WAV file locally.
If I check downloaded WAV file, it is not broken.

```
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100
Input #0, wav, from '/mnt/c/Users/w0obe/Downloads/2020-02-03T02_53_29.366Z.wav':
  Duration: 00:00:07.34, bitrate: 768 kb/s
    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, 1 channels, s16, 768 kb/s

```

[![my app](https://i.stack.imgur.com/BmlF7.png)](https://i.stack.imgur.com/BmlF7.png)

---

My directory structure is here.

```
.
├── file.wav(uploaded WAV file)
├── main.py
├── Pipfile
├── Pipfile.lock
├── static
│   └── js
│       └── app.js
└── templates
    └── index.html

```

This is main.py.

```
#!/usr/bin/env python
# -*- coding: utf-8 -*-
from flask import Flask
from flask import request
from flask import render_template
import os

app = Flask(__name__)

@app.route("/", methods=['POST', 'GET'])
def index():
    if request.method == "POST":
        f = open('./file.wav', 'wb')
        f.write(request.get_data("audio_data"))
        f.close()
        if os.path.isfile('./file.wav'):
            print("./file.wav exists")

        return render_template('index.html', request="POST")   
    else:
        return render_template("index.html")

if __name__ == "__main__":
    app.run()

```

This is index.html.

```
<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>Simple Recorder.js demo with record, stop and pause - addpipe.com</title>
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
  </head>
  <body>
    <h1>Simple Recorder.js demo</h1>

    <div id="controls">
     <button id="recordButton">Record</button>
     <button id="pauseButton" disabled>Pause</button>
     <button id="stopButton" disabled>Stop</button>
    </div>
    <div id="formats">Format: start recording to see sample rate</div>
    <p><strong>Recordings:</strong></p>
    <ol id="recordingsList"></ol>
    <!-- inserting these scripts at the end to be able to use all the elements in the DOM -->
    <script src="https://cdn.rawgit.com/mattdiamond/Recorderjs/08e7abd9/dist/recorder.js"></script>
    <script src="/static/js/app.js"></script>
  </body>
</html>

```

This is app.js.

```
//webkitURL is deprecated but nevertheless
URL = window.URL || window.webkitURL;

var gumStream;                      //stream from getUserMedia()
var rec;                            //Recorder.js object
var input;                          //MediaStreamAudioSourceNode we'll be recording

// shim for AudioContext when it's not avb. 
var AudioContext = window.AudioContext || window.webkitAudioContext;
var audioContext //audio context to help us record

var recordButton = document.getElementById("recordButton");
var stopButton = document.getElementById("stopButton");
var pauseButton = document.getElementById("pauseButton");

//add events to those 2 buttons
recordButton.addEventListener("click", startRecording);
stopButton.addEventListener("click", stopRecording);
pauseButton.addEventListener("click", pauseRecording);

function startRecording() {
    console.log("recordButton clicked");

    /*
        Simple constraints object, for more advanced audio features see
        https://addpipe.com/blog/audio-constraints-getusermedia/
    */

    var constraints = { audio: true, video:false }

    /*
        Disable the record button until we get a success or fail from getUserMedia() 
    */

    recordButton.disabled = true;
    stopButton.disabled = false;
    pauseButton.disabled = false

    /*
        We're using the standard promise based getUserMedia() 
        https://developer.mozilla.org/en-US/docs/Web/API/MediaDevices/getUserMedia
    */

    navigator.mediaDevices.getUserMedia(constraints).then(function(stream) {
        console.log("getUserMedia() success, stream created, initializing Recorder.js ...");

        /*
            create an audio context after getUserMedia is called
            sampleRate might change after getUserMedia is called, like it does on macOS when recording through AirPods
            the sampleRate defaults to the one set in your OS for your playback device

        */
        audioContext = new AudioContext();

        //update the format 
        document.getElementById("formats").innerHTML="Format: 1 channel pcm @ "+audioContext.sampleRate/1000+"kHz"

        /*  assign to gumStream for later use  */
        gumStream = stream;

        /* use the stream */
        input = audioContext.createMediaStreamSource(stream);

        /* 
            Create the Recorder object and configure to record mono sound (1 channel)
            Recording 2 channels  will double the file size
        */
        rec = new Recorder(input,{numChannels:1})

        //start the recording process
        rec.record()

        console.log("Recording started");

    }).catch(function(err) {
        //enable the record button if getUserMedia() fails
        recordButton.disabled = false;
        stopButton.disabled = true;
        pauseButton.disabled = true
    });
}

function pauseRecording(){
    console.log("pauseButton clicked rec.recording=",rec.recording );
    if (rec.recording){
        //pause
        rec.stop();
        pauseButton.innerHTML="Resume";
    }else{
        //resume
        rec.record()
        pauseButton.innerHTML="Pause";

    }
}

function stopRecording() {
    console.log("stopButton clicked");

    //disable the stop button, enable the record too allow for new recordings
    stopButton.disabled = true;
    recordButton.disabled = false;
    pauseButton.disabled = true;

    //reset button just in case the recording is stopped while paused
    pauseButton.innerHTML="Pause";

    //tell the recorder to stop the recording
    rec.stop();

    //stop microphone access
    gumStream.getAudioTracks()[0].stop();

    //create the wav blob and pass it on to createDownloadLink
    rec.exportWAV(createDownloadLink);
}

function createDownloadLink(blob) {

    var url = URL.createObjectURL(blob);
    var au = document.createElement('audio');
    var li = document.createElement('li');
    var link = document.createElement('a');

    //name of .wav file to use during upload and download (without extendion)
    var filename = new Date().toISOString();

    //add controls to the <audio> element
    au.controls = true;
    au.src = url;

    //save to disk link
    link.href = url;
    link.download = filename+".wav"; //download forces the browser to donwload the file using the  filename
    link.innerHTML = "Save to disk";

    //add the new audio element to li
    li.appendChild(au);

    //add the filename to the li
    li.appendChild(document.createTextNode(filename+".wav "))

    //add the save to disk link to li
    li.appendChild(link);

    //upload link
    var upload = document.createElement('a');
    upload.href="#";
    upload.innerHTML = "Upload";
    upload.addEventListener("click", function(event){
          var xhr=new XMLHttpRequest();
          xhr.onload=function(e) {
              if(this.readyState === 4) {
                  console.log("Server returned: ",e.target.responseText);
              }
          };
          var fd=new FormData();
          fd.append("audio_data",blob, filename);
          xhr.open("POST","/",true);
          xhr.send(fd);
    })
    li.appendChild(document.createTextNode (" "))//add a space in between
    li.appendChild(upload)//add the upload link to li

    //add the li element to the ol
    recordingsList.appendChild(li);
}

```

**How can I upload WAV file to flask server?**
Could you give me any information or suggestion?

Thank you in advance.

Sincerely, Kazu