Decoding base64 encoded webm video in NodeJs - node.js

Question

I'm setting up an Express.js endpoint that would support decoding a base64 string that came from the client (camera record), which is basically an encoded webm video.
The problem is that to validate this, I am trying to create a .webm video file from the encoded base64 string on the server. Unfortunately this results in a video file that cannot be played due to an error of "No video with supported format and MIME type found" (Ubuntu 18.04).
I did not have any issue with any other .webm files but also the base64 URL is sure to be correct as I am using it on the cliet as the source of a element to replay what was recorded and works fine.
The issue I suspect is something wrong with the code that generates the file on the server route.
import express from "express";
import multer from "multer";
import fs from "fs";
const router = express.Router();
// ...
router.post("/upload", multer().fields([]), (req, res) => {
const formData = req.body;
// formData.vid_string is the base64 encoded string
fs.writeFileSync(
"./test.webm",
Buffer.from(formData.vid_string.split(",")[1], "base64")
);
res.sendStatus(200);
});
I have also tried to change fs.writeFileSync code and add "base64" as a third argument but it has the same result.
Any input would be appreciated! Thanks!

Answer 1

I am pretty sure the correct way to do this is to remove the portion of the base64 string that is the URL specifications (If this is applicable to your situation being the part string that states base64 data and the "video/webm" portion and the trailing comma,) and call atob() on the resulting string this atob will represent the binary string version of the video. Then simply write that string to your new file!
However, I would recommend parsing the base64URL to binary string from the client side, since I am fairly sure that base64 uses more space to account for a smaller group of available bytes, if you have any control over how the video will be sent to the node server.