Transcode video stored online, live, in chunks

Question

I have a video stored on the cloud, I'm using this Flask route to download chunks of the video at a time and return it to the user as a stream:

@app.route("/api/v1/download")
def downloadAPI():
    def download_file(streamable):
        with streamable as stream:
            stream.raise_for_status()
            for chunk in stream.iter_content(chunk_size=512):
                yield chunk

    headers = {"range": range}
    resp = requests.request(
        method=request.method,
        url="example.com/api/file",
        headers=headers,
        data=request.get_data(),
        cookies=request.cookies,
        allow_redirects=False,
        stream=True)

    return Response(download_file(resp), resp.status_code)

How would I transcode these chunks on the fly?

I'm planning on transcoding basically any type of video to mp4