Video stream source change using Python Flask and JS

I have the following server side route code for stream

movies_list = ['./mov1.mp4', './mov2.mp4', './mov3.mp4',]

@app.route("/video", methods=["GET"])
def video():
    headers = request.headers
    if not "range" in headers:
        return current_app.response_class(status=400)

    video_path = os.path.abspath(os.path.join("media", movies_list[0]))
    size = os.stat(video_path)
    size = size.st_size

    chunk_size = (10 ** 6) * 3 #1000kb makes 1mb * 3 = 3mb (this is based on your choice)
    start = int(re.sub("D", "", headers["range"]))
    end = min(start + chunk_size, size - 1)

    content_lenght = end - start + 1

    def get_chunk(video_path, start, chunk_size):
        with open(video_path, "rb") as f:
            f.seek(start)
            chunk = f.read(chunk_size)
        return chunk

    headers = {
        "Content-Range": f"bytes {start}-{end}/{size}",
        "Accept-Ranges": "bytes",
        "Content-Length": content_lenght,
        "Content-Type": "video/mp4",
    }

    return current_app.response_class(get_chunk(video_path, start,chunk_size), 206, headers)

Also client side html page

<video width="720" controls>
  <source src="/video" type="video/mp4">
</video>

How can I send a request from the client side to the server so that it changes the source and starts playing?