Combine video and audio files together using JavaScript?

Question

Let's say I have two files video.webm and audio.webm. These two files are supposed to be one file combined together, which will become a 'regular' video + audio file. Is this possible using JavaScript?

Example (these are not the actual fetch)

const video = await fetch('https://harry-potter.com/video'); // Gets video file of movie Harry Potter.
const videoBlob = await video.blob();
const audio = await fetch('https://harry-potter.com/audio'); // Gets audio file of movie Harry Potter.
const auidoBlob = await audio.blob();

const finalBlob = videoBlob + audioBlob; // I want to combine two blobs.

Answer 1

Here is an example for you by using FFmpeg

 import ffmpegPath from 'ffmpeg-static';
    import cp from 'child_process';
    import stream from 'stream';
    import ytdl from "ytdl-core";
    
    const ytmixer = (link, options = {}) => {
    const result = new stream.PassThrough({ highWaterMark: (options as 
    any).highWaterMark || 1024 * 512 });
    ytdl.getInfo(link, options).then(info => {
        let audioStream = ytdl.downloadFromInfo(info, { ...options, quality: 
    'highestaudio' });
        let videoStream = ytdl.downloadFromInfo(info, { ...options, quality: 
    'highestvideo' });
        // create the ffmpeg process for muxing
        let ffmpegProcess = cp.spawn(ffmpegPath, [
            // supress non-crucial messages
            '-loglevel', '8', '-hide_banner',
            // input audio and video by pipe
            '-i', 'pipe:3', '-i', 'pipe:4',
            // map audio and video correspondingly
            '-map', '0:a', '-map', '1:v',
            // no need to change the codec
            '-c', 'copy',
            // output mp4 and pipe
            '-f', 'matroska', 'pipe:5'
        ], {
            // no popup window for Windows users
            windowsHide: true,
            stdio: [
                // silence stdin/out, forward stderr,
                'inherit', 'inherit', 'inherit',
                // and pipe audio, video, output
                'pipe', 'pipe', 'pipe'
            ]
        });
        audioStream.pipe(ffmpegProcess.stdio[3]);
        videoStream.pipe(ffmpegProcess.stdio[4]);
        ffmpegProcess.stdio[5].pipe(result);
    });
    return result;
    };
    
    
    ytmixer('Your Url').pipe(res);