$ youtube-dl -v http://www.youtube.com/watch?v=B5Ni8UKI198
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['-v', 'http://www.youtube.com/watch?v=B5Ni8UKI198']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2017.04.26
[debug] Python version 3.6.1 - Linux-4.10.11-1-ARCH-x86_64-with-arch
[debug] exe versions: ffmpeg 3.3, ffprobe 3.3, rtmpdump 2.4
[debug] Proxy map: {}
[youtube] B5Ni8UKI198: Downloading webpage
[youtube] B5Ni8UKI198: Downloading video info webpage
[youtube] B5Ni8UKI198: Extracting video information
WARNING: unable to extract html5 player; please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see  https://yt-dl.org/update  on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
[youtube] {43} signature length 40.40, html5 player None
ERROR: Signature extraction failed: Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/youtube_dl/extractor/youtube.py", line 1081, in _decrypt_signature
    video_id, player_url, s
  File "/usr/lib/python3.6/site-packages/youtube_dl/extractor/youtube.py", line 969, in _extract_signature_function
    raise ExtractorError('Cannot identify player %r' % player_url)
youtube_dl.utils.ExtractorError: Cannot identify player 'https://www.youtube.com/yts/jsbin/player-vflppxuSE/en_US/base.js'; please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see  https://yt-dl.org/update  on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
 (caused by ExtractorError("Cannot identify player 'https://www.youtube.com/yts/jsbin/player-vflppxuSE/en_US/base.js'; please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see  https://yt-dl.org/update  on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.",)); please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see  https://yt-dl.org/update  on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/youtube_dl/extractor/youtube.py", line 1081, in _decrypt_signature
    video_id, player_url, s
  File "/usr/lib/python3.6/site-packages/youtube_dl/extractor/youtube.py", line 969, in _extract_signature_function
    raise ExtractorError('Cannot identify player %r' % player_url)
youtube_dl.utils.ExtractorError: Cannot identify player 'https://www.youtube.com/yts/jsbin/player-vflppxuSE/en_US/base.js'; please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see  https://yt-dl.org/update  on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/youtube_dl/extractor/youtube.py", line 1081, in _decrypt_signature
    video_id, player_url, s
  File "/usr/lib/python3.6/site-packages/youtube_dl/extractor/youtube.py", line 969, in _extract_signature_function
    raise ExtractorError('Cannot identify player %r' % player_url)
youtube_dl.utils.ExtractorError: Cannot identify player 'https://www.youtube.com/yts/jsbin/player-vflppxuSE/en_US/base.js'; please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see  https://yt-dl.org/update  on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/youtube_dl/YoutubeDL.py", line 760, in extract_info
    ie_result = ie.extract(url)
  File "/usr/lib/python3.6/site-packages/youtube_dl/extractor/common.py", line 429, in extract
    ie_result = self._real_extract(url)
  File "/usr/lib/python3.6/site-packages/youtube_dl/extractor/youtube.py", line 1642, in _real_extract
    encrypted_sig, video_id, player_url, age_gate)
  File "/usr/lib/python3.6/site-packages/youtube_dl/extractor/youtube.py", line 1091, in _decrypt_signature
    'Signature extraction failed: ' + tb, cause=e)
youtube_dl.utils.ExtractorError: Signature extraction failed: Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/youtube_dl/extractor/youtube.py", line 1081, in _decrypt_signature
    video_id, player_url, s
  File "/usr/lib/python3.6/site-packages/youtube_dl/extractor/youtube.py", line 969, in _extract_signature_function
    raise ExtractorError('Cannot identify player %r' % player_url)
youtube_dl.utils.ExtractorError: Cannot identify player 'https://www.youtube.com/yts/jsbin/player-vflppxuSE/en_US/base.js'; please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see  https://yt-dl.org/update  on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
 (caused by ExtractorError("Cannot identify player 'https://www.youtube.com/yts/jsbin/player-vflppxuSE/en_US/base.js'; please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see  https://yt-dl.org/update  on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.",)); please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see  https://yt-dl.org/update  on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.