def _pv_params(cls, session, pvswf, pv, **request_params):
        """Returns any parameters needed for Akamai HD player verification.

        Algorithm originally documented by KSV, source:
        http://stream-recorder.com/forum/showpost.php?p=43761&postcount=13
        """

        try:
            data, hdntl = pv.split(";")
        except ValueError:
            data = pv
            hdntl = ""

        cache = Cache(filename="stream.json")
        key = "akamaihd-player:" + pvswf
        cached = cache.get(key)

        request_params = deepcopy(request_params)
        headers = request_params.pop("headers", {})
        if cached:
            headers["If-Modified-Since"] = cached["modified"]
        swf = session.http.get(pvswf, headers=headers, **request_params)

        if cached and swf.status_code == 304:  # Server says not modified
            hash = cached["hash"]
        else:
            # Calculate SHA-256 hash of the uncompressed SWF file, base-64
            # encoded
            hash = sha256()
            hash.update(swfdecompress(swf.content))
            hash = base64.b64encode(hash.digest()).decode("ascii")
            modified = swf.headers.get("Last-Modified", "")

            # Only save in cache if a valid date is given
            if len(modified) < 40:
                cache.set(key, dict(hash=hash, modified=modified))

        msg = "st=0~exp=9999999999~acl=*~data={0}!{1}".format(data, hash)
        auth = hmac.new(AKAMAIHD_PV_KEY, msg.encode("ascii"), sha256)
        pvtoken = "{0}~hmac={1}".format(msg, auth.hexdigest())

        # The "hdntl" parameter can be accepted as a cookie or passed in the
        # query string, but the "pvtoken" parameter can only be in the query
        # string
        params = [("pvtoken", pvtoken)]
        params.extend(parse_qsl(hdntl, keep_blank_values=True))

        return params
Returns any parameters needed for Akamai HD player verification.

        Algorithm originally documented by KSV, source:
        http://stream-recorder.com/forum/showpost.php?p=43761&postcount=13