For VoD on "Niconico Channel Plus" (Japanese: ニコニコチャンネルプラス).
https://portal.nicochannel.jp/

Thanks to the following people who provided useful information:

- lokilin, raised a request in issue 2537 of yt-dlp/yt-dlp;
- 雷兰濑 (railannad), raised a request in issue 4366;
- Trung0246, analyzed HTTP data in issue 4366;
- Lesmiscore, made cross-reference between the above two issues.

- Store all URLs as class members for better human-reading.
- Directly use the "HTTPSession" object which is from the Streamlink
  session instead of passing it from outside.
- Use validation schemas instead of "json.loads" and "__getitem__" ([])
  for better data decoding, JSON validation and exception handling.
- Directly return the result from "HLSStream.parse_variant_playlist"
  since the plugin does not modify the dictionary of streams.

Both ID and channel name are in the URL, so no need to output them.

It's not informative.

Titles are easy to find in the webpage.

That channel name is "kanase.ito".

…onvert_to_vod_flg" are True

The name of those fields is confusing.

…a live