how can i download a video mp4 file using node.js?

I want to let users download a video from my AWS S3 bucket. The video format is MP4:

app.get("/download_video", function(req,res) {
    filename = "s3.xxx.amazon.com/bucketname/folder/video_example.mp4";
    // im stuck on what i can do here
});

There are a lot of examples on how to download images and textfiles online using nodejs, but I can't find anything on videos.