How to stream large .mp4 files?

28 Jul, 2021
Streaming large video files from the server to the client which might be a web app or mobile apps inefficient manner! 
We can’t send the entire video once to a client. because there are conditions like the bandwidth and data restrictions of the user.
Example:
Let’s say youtube, the user may watch some part of the video and went away for some reason, if he opened that video again, it should not load the entire video from start. 
Here is the part we need some mechanism to handle this situation. 
Nodejs stream API comes into the picture, its more efficient than reading a file in a conventional manner and waiting for the callbacks to resolve.
Created a basic video streaming server to explain it little better.  
The flow of the system:
User visits the site (index.html)
The html5 video component in index.html is pointed to URL of the video that is streaming by server
The video request is handler by the server by processing range header and sends out part of the video as partial content
Setting up project:
Open terminal
mkdir <project name>
cd <project name>
npm init -y
Open your favourite  text editor
Create index.html on that folder (check below html code, use it there)
Create a server.js file(check the js code provided below)
Run the command “node server.js”
Open browser and navigate to “localhost:3000”
Complete source code: 
 https://github.com/varaprasadh/gfg-blogs/tree/master/streamvideo
We will need a index.html file show the video that coming from the server!
HTML
<!DOCTYPE html><html lang="en"><head>    <meta charset="UTF-8">    <meta name="viewport"          content="width=device-width,                   initial-scale=1.0">    <meta http-equiv="X-UA-Compatible"            content="ie=edge">    <title>video player</title></head><body>    <video src="http://localhost:3000/video" controls>   </video></body></html>
Javascript
const http=require('http');const fs=require("fs");const path=require("path"); /* http.createServer takes a handler   function and returns a server instance;*/const server=http.createServer((req, res)=>{    // return res.end(req.url+req.method);    if(req.method==='GET' && req.url==="/"){        /*we will send a index.html page when          user visits "/" endpoint*/        /*index.html will have video component          that displays the video*/                 fs.createReadStream(path.resolve(                        "index.html")).pipe(res);        return;    }    //if video content is requesting    if(req.method==='GET' && req.url==="/video"){        const filepath = path.resolve("video.mp4");        const stat = fs.statSync(filepath)        const fileSize = stat.size        const range = req.headers.range        /*when we seek the video it will put          range header to the request*/        /*if range header exists send some            part of video*/        if (range) {            //range format is "bytes=start-end",            const parts =                range.replace(/bytes=/, "").split("-");                        const start = parseInt(parts[0], 10)            /*in some cases end may not exists, if its                          not exists make it end of file*/            const end =                 parts[1] ?parseInt(parts[1], 10) :fileSize - 1                         //chunk size is what the part of video we are sending.            const chunksize = (end - start) + 1            /*we can provide offset values as options to           the fs.createReadStream to read part of content*/            const file = fs.createReadStream(filepath, {start, end})                         const head = {                'Content-Range': `bytes ${start}-${end}/${fileSize}`,                'Accept-Ranges': 'bytes',                'Content-Length': chunksize,                'Content-Type': 'video/mp4',            }            /*we should set status code as 206 which is                    for partial content*/            // because video is continuously fetched part by part            res.writeHead(206, head);          file.pipe(res);                   }else{                 //if not send the video from start.        /* anyway html5 video player play content          when sufficient frames available*/        // It doesn't wait for the entire video to load.                    const head = {               'Content-Length': fileSize,               'Content-Type': 'video/mp4',           }           res.writeHead(200, head);           fs.createReadStream(path).pipe(res);        }    }    /*if anything other than handler routes then send      400 status code, is for bad request*/    else{        res.writeHead(400);        res.end("bad request");    }}) /*check if system has environment variable   for the port, otherwise defaults to 3000*/const PORT = process.env.PORT || 3000; //start the serverserver.listen(PORT, () => {  console.log(`server listening on port:${PORT}`);})
Finally we can see the result in the browser
Final Result
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