How can I append video segment (stream) in PHP [Laravel]

This is my first time working with videos and it's a bit overwhelming.

Problem

I would like to be able to record user's screen and every 5 seconds send the recorded screen to my backend server. Then, on my backend server append each 5 seconds into a full video.

If I send 3 parts of 5 second, I would like to have the full 15 seconds video.

What I have tried

I have the following frontend code:

function accessRecord(id) {
    navigator.mediaDevices.getDisplayMedia({
        audio: false,
        video: true
    }).then(startStream).catch(failedStream)
}

function startStream(stream) {
    const mediaRecorder = new MediaRecorder(stream, {
        // I have tried adding a mimeType as well
        // mimeType: 'video/mp4'
    });

    mediaRecorder.start(5000);

    mediaRecorder.ondataavailable = (e) => {
        fetch('http://localhost/api/session/12/video/stream', {
            method: 'POST',
            body: new Blob([e.data]),
        }).then(() => {
            console.log('success')
        }).catch((e) => {
            console.log('error')
            console.log(e);
        })
    };
}

Then, on my backend server [Laravel] I do the following logic:

Route::post('session/{id}/video/stream', function (Request $request) {
    $videoData = $request->getContent();

    $filename = 'video_uuid-video.mp4';

    if (!file_exists(storage_path('app/videos/' . $filename))) {
        touch(storage_path('app/videos/' . $filename));
    }

    \Illuminate\Support\Facades\Storage::append('videos/' . $filename, $videoData);

    return response()->json(['message' => 'Video frame uploaded successfully']);
});

Whenever I stop the streaming, and I try to open the video on my MAC (MacOS) the video doesn't open:

I'm not sure what I'm doing wrong here. I would like to record every 5 seconds the video, then append to the current video and in the end (when the stream ends) I would like to be able to play the video.

You can not combine or append video file to another video file using normal append like append text file.

You need an encoder, for an example FFMPEG

here the example code:

    $existing_file = 'video_uuid-video.mp4';
    $filename = rand(0,9999999).".mp4";

    if (!file_exists(storage_path('app/videos/'.$filename))) {
        touch(storage_path('app/videos/'.$filename));
    }

    Storage::put('videos/'.$filename, $videoData);
    shell_exec("ffmpeg -i $filename -i $existing_file -filter_complex \"concat=n=2:v=0:a=1\" -vn -y output.mp4");