Send MediaRecorder blobs to server and build file on backend

Question

I\'m working on a website using nodejs and SailsJs.

My objective is send the blobs generated by MediaRecorder.ondataavailable event (which returns small blobs) to the se

Answer 1

So I solved it by doing the following (once I get the merge action call):

const dir = `${__dirname}/.tmp/`;
const fileName = getFileNameFromEvent(eventId);
const path = dir + fileName;
//First get the path for every file chunk ordered (otherwise it'll lose quality)
let recParts = await RecordingParts.find({
      where: {
        filename: fileName
      }
    }).sort('index ASC');

let wstream = fs.createWriteStream(path);
for (let i = 0; i < recParts.length; i++){
      let aux = await readFile(recParts[i].tmpPath, null);
      wstream.write(aux);
      //Delete chunks
      fs.unlink(recParts[i].tmpPath, (err) => {
        if (err) throw err;
      });
    }

    wstream.end();

//Utils function
const readFile = (path, opts = 'utf8') =>
  new Promise((res, rej) => {
    fs.readFile(path, opts, (err, data) => {
      if (err) rej(err);
      else res(data)
    })
  });

After

wstream.end();

You will have the merged file at path

Answer 2

For those who are still interesting in the flow of the continuous saving of the media stream using MediaRecorder API and WebSockets...

Client side:

const ws = new WebSocket(someWsUrl);
const mediaStream = new MediaStream();
const videoTrack = someStream.getVideoTracks()[0];
const audioTrack = someStream.getAudioTracks()[0];
mediaStream.addTrack(videoTrack);
mediaStream.addTrack(audioTrack);
const recorderOptions = {
  mimeType: 'video/webm',
  videoBitsPerSecond: 200000 // 0.2 Mbit/sec.
};
const mediaRecorder = new MediaRecorder(mediaStream, recorderOptions);
mediaRecorder.start(1000); // 1000 - the number of milliseconds to record into each Blob
mediaRecorder.ondataavailable = (event) => {
  console.debug('Got blob data:', event.data);
  if (event.data && event.data.size > 0) {
    ws.send(event.data);
  }
};

Server side:

const WebSocket = require('ws');
const wss = new WebSocket.Server({ port: 3000 });
wss.on('connection', (ws, req) => {
  const fileStream = fs.createWriteStream(filePath, { flags: 'a' });
  ws.on('message', message => {
    // Only raw blob data can be sent
    fileStream.write(Buffer.from(new Uint8Array(message)));
  });
});

Answer 3

This is my solution if it helps anybody:

I send chuncks in binary format (I have selected Uint8Array), and add each chunk to a file in the server side after packing the received data (converted to binary in the same unsigned char decoding)

Client Side Javascript:

let order=0;
mediaRecorder.ondataavailable = async (e) => {
    if(e.data && e.data.size > 0) {         
        var reader = new FileReader();
        reader.readAsArrayBuffer(e.data); 
        reader.onloadend = async function(event) {
            let arrayBuffer = reader.result;   
            let uint8View = new Uint8Array(arrayBuffer);
            let response = await fetch('save-video.php', {
                method: 'POST',                 
                body: JSON.stringify({
                    chunk: uint8View,
                    order: order
                })                  
            });
            order += 1;
        }

    }       
}

Server Side PHP:

<?php
    
$request = json_decode(file_get_contents("php://input"), true);
$chunk = $request['chunk'];
$order = $request['order'];
$binarydata = pack("C*", ...$chunk);
    
$filePath = "uploads/file.webm";
$out = fopen("{$filePath}", $order == 0 ? "wb" : "ab");
if ($out) {
    fwrite($out, $binarydata);
    fclose($out);
}

?>