ctrl.forVideo(req,res);

controllers.js

ctrl.forVideo = function (req, res) {
    // First we store our file name in a variable using a inmediatly-invoked function
    let file = (function () {
        // Split the URL in each slash "/";
        let splitted = req.url.split('/');
        //  Then we return only the last part of that array.
        return splitted[splitted.length - 1];
    })();
  
  // Then we check the file stats.
  // We know that it will be in /public/media,
  // so we only add the file name to the string
  fs.stat('public/media/' + file, (err, data) => {
    //  First we check for error
        if (err) {
          //If error, we send a response with status code 404.
            res.writeHead(404)
            res.end();
            throw err

        } else {
            //In case that everithing went OK
            //We check for 'range' header;
            //If we find them, we procced
            if (req.headers['range']) {
                // We store the header in a variable
                let range = req.headers['range'];
                // Then we remove the first part and split the string in every dash "-"
                var array = range.replace('bytes=', "").split("-");
                // After that we store the number where we start to read our buffer;
                var start = parseInt(array[0], 10);
                // We check if there is and end, if not, we just send the total size of the file
                // Total size is total -1, because we start counting from the 0.
                // data.size returns the size, "data" is the object that fs.stat outputs.
                var end = array[1] ? parseInt(array[1], 10) : data.size - 1;
                // Here we decide the size of every chunck we will be sending
                var chunck = 1024 * 1000;
                // And then we set the headers and status code 206
                res.writeHead(206, {
                    // We tell the units that we use to messure the ranges
                    'Accept-Ranges': 'bytes',
                    // We tell the range of the content that we are sending
                    "Content-Range": "bytes " + start + "-" + end + "/" + data.size,
                    // Tell the length of the chunck. We use this to control the flow of the stream.
                    // The "chunck" is a variable that we set in line 38 of this gist.
                    'Content-Length': chunck,
                    // Set the MIME-type
                    'Content-Type': 'video/mp4',
                    // And also set that we dont want to cache out file
                    // This is just to make our example work as if allways were the first time we ask the file.
                    'Cache-Control': 'no-cache'
                });

                // If the ranges headers can't be fulfilled, we will be sending a stream anyway,
                // but the browser will need to assume things and slow down the process.
              
                // Time to make our readable stream
                // First we create a readableStream and store in a variable
                // We pass the start and end parameters so NodeJS can know wich part needs to read and send as buffer.
                let readable = fs.createReadStream('public/media/banjo.mp4', { start, end });
                // If for some reason we cant create our Readable Strea, we end the response.
                if (readable == null) {
                    console.log('readable = null');
                    return res.end();
                // If not...
                } else {
                    // First we use the event .on('open') to listen when the readable is ready to rock
                    // Then we provide a function to pipe to res.
                    readable.on('open', () => {
                        console.log('we are on open');
                        // This function is esential. Here we are puting all the buffer chunk to the response object.
                        readable.pipe(res);
                    });
                    // We also be waiting for that umpleasing error event.
                    readable.on('error', (err) => {
                      // If it happen, we will send the error with the .end() method.
                        res.end(err);
                        console.log(err);
                    });

                }
            }

        }


    })

}