How do you add a header to wav file?

Question

I am sending audio data stored as a blob to my backend (node/express). When I save the file as .wav and attempt to use in the SpeechRecogition package in python it throws an error saying the "file does not start with RIFF id". So how can I add the headers to my blob file before I save it so that it is a correctly formatted .wav file? I can provide the code if necessary.

node.js file

var multer = require('multer');
var fs = require('fs'); //use the file system so we can save files
var uniqid = require('uniqid');
var spawn = require('child_process').spawn;
const storage = multer.memoryStorage()
var upload = multer({ storage: storage });

router.post('/api/test', upload.single('upl'), function (req, res) {

   console.log(req.file);
   console.log(req.file.buffer);

   var id = uniqid();
   fs.writeFileSync(id+".wav", Buffer.from(new Uint8Array(req.file.buffer))); //write file to server as .wav file

   const scriptPath = 'handleAudio.py'
   const process = spawn('python3', [__dirname+"/../"+scriptPath, "/home/bitnami/projects/sample/"+id+".wav", req.file.originalname, 'True']); //throws error about header in .wav

});

Also I had this same example working with a php endpoint that just saved the blob to a file with .wav extension and the python file accepted it. What could be different in the move_uploaded_file in php and what I am doing above with node?

Answer 1

Every .wav file needs a header specified by the WAVE file format, available here . While it's fine for you to build the header yourself, it's much easier to just use a proper lib to do the work for you.

One example is node-wav , which has a nice API to write WAVE files from raw PCM data (what you have at the moment). Example code is provided by the node-wav documentation.