Repository: youtube-dl
Issue: [niconico] Support for HLS-only videos
Labels: account-needed

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## Checklist

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- First of, make sure you are using the latest version of youtube-dl. Run `youtube-dl --version` and ensure your version is 2019.09.28. If it's not, see https://yt-dl.org/update on how to update. Issues with outdated version will be REJECTED.
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- [x] I'm reporting a site feature request
- [x] I've verified that I'm running youtube-dl version **2019.09.28**
- [x] I've searched the bugtracker for similar site feature requests including closed ones


## Description

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Recently niconico introduced support for HLS videos and now some of the new licensed videos are provided only in HLS format.

Examples:
* https://www.nicovideo.jp/watch/1562727729
* https://www.nicovideo.jp/watch/so35376541

Since yt-dl is currently not supporting downloading HLS videos of niconico, these URLs fail to download video infos and emit the following errors.

```
$ youtube-dl --verbose -u ### -p ### https://www.nicovideo.jp/watch/1562727729
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['--verbose', '-u', 'PRIVATE', '-p', 'PRIVATE', 'https://www.nicovideo.jp/watch/1562727729']
[debug] Encodings: locale cp932, fs mbcs, out cp65001, pref cp932
[debug] youtube-dl version 2019.09.28
[debug] Python version 3.4.4 (CPython) - Windows-10-10.0.18362
[debug] exe versions: ffmpeg 2.8.4, ffprobe 3.4.1, rtmpdump 2.3
[debug] Proxy map: {'no': '192.168.99.100'}
[niconico] Logging in
[niconico] 1562727729: Downloading webpage
[niconico] 1562727729: Downloading JSON metadata for h264_720p-aac_192kbps
ERROR: Unable to download JSON metadata: HTTP Error 403: Forbidden (caused by HTTPError()); please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; type  youtube-dl -U  to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
  File "C:\Users\dst\AppData\Roaming\Build archive\youtube-dl\ytdl-org\tmpyi91grvc\build\youtube_dl\extractor\common.py", line 627, in _request_webpage
  File "C:\Users\dst\AppData\Roaming\Build archive\youtube-dl\ytdl-org\tmpyi91grvc\build\youtube_dl\YoutubeDL.py", line 2237, in urlopen

  File "C:\Python\Python34\lib\urllib\request.py", line 470, in open
  File "C:\Python\Python34\lib\urllib\request.py", line 580, in http_response
  File "C:\Python\Python34\lib\urllib\request.py", line 508, in error
  File "C:\Python\Python34\lib\urllib\request.py", line 442, in _call_chain
  File "C:\Python\Python34\lib\urllib\request.py", line 588, in http_error_default
```

For technical details, HLS-only videos have metadata with `api_data['video']['dmcInfo']['session_api']['protocols'] == ['hls']`, not `['http', 'hls']`.