partial_serve_flask_2.py

range_header = request.headers.get('Range', None)
    if range_header:
        from_bytes, until_bytes = range_header.replace('bytes=', '').split('-')
        if not until_bytes:  # No until bytes is set, set it to start + 3MB
            until_bytes = int(from_bytes) + int(1024 * 1024 * 3)  # 1MB * 3 = 3MB

        # Get only what required from YouTube
        headers = {'Range': 'bytes=%s-%s' % (from_bytes, until_bytes)}
        r = requests.get(url, headers=headers)
        data = r.content
        
        # Generate response
        rv = Response(data, 206, mimetype=mime, direct_passthrough=True)
        rv.headers.add('Content-Range', r.headers.get('Content-Range'))
        return rv