Issue

• This is a bug report.
• I have read the contribution guidelines.

Description

As of yesterday, Streamlink doesn't detect a YouTube live stream when you put in channel home page as parameter. Tested with several YT channels. A friend of mine started experiencing same issue yesterday as well. Inputting direct video link works, but detecting that video from the channel page is now broken.

Expected / Actual behavior

Streamlink should find an ID of the live stream and start downloading/streaming it.
Instead no video is found at all.

Reproduction steps / Explicit stream URLs to test

1. Find a YT channel that has a live stream
2. Input: streamlink.exe https://www.youtube.com/channel/xxxxxxx (other parameters don't seem to matter)
3. Output: error: Could not find a video on this page

Logs

Channel ID removed:

streamlink --loglevel debug https://www.youtube.com/channel/xxxxx
[cli][debug] OS:         Windows 7
[cli][debug] Python:     3.6.6
[cli][debug] Streamlink: 1.6.0
[cli][debug] Requests(2.24.0), Socks(1.7.1), Websocket(0.57.0)
[cli][info] Found matching plugin youtube for URL https://www.youtube.com/channel/xxxxx
error: Could not find a video on this page

Additional comments, etc.

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