[Broken] YouTube alternative channel URL not recognized

[ghost]

• [x] I'm reporting a broken site support
• [x] I've verified that I'm running youtube-dlc version 2020.10.31 (I just had to follow issue template, but same with latest version)
• [x] I've checked that all provided URLs are alive and playable in a browser
• [x] I've checked that all URLs and arguments with special characters are properly quoted or escaped
• [x] I've searched the bugtracker for similar issues including closed ones

Description

YouTube channel URLs are not always recognized. For example

> youtube-dlc "https://www.youtube.com/deepinc/videos?flow=grid&view=0&gl=US"
[generic] videos?flow=grid&view=0&gl=US: Requesting header
WARNING: Falling back on generic information extractor.
[generic] videos?flow=grid&view=0&gl=US: Downloading webpage
[generic] videos?flow=grid&view=0&gl=US: Extracting information
ERROR: Unsupported URL: https://www.youtube.com/deepinc/videos?flow=grid&view=0&gl=US

However, if I compute the channel ID of deepinc, then it works:

> youtube-dlc "https://www.youtube.com/channel/UCyF1eat8zd-GaeYcjiWbyvQ/videos?flow=grid&view=0&gl=US"
[youtube:tab] UCyF1eat8zd-GaeYcjiWbyvQ: Downloading webpage
[download] Downloading playlist: DEEP INC. - Videos
[youtube:tab] Downloading page 1
[youtube:tab] Downloading page 2
[youtube:tab] Downloading page 3
[youtube:tab] Downloading page 4
[youtube:tab] playlist DEEP INC. - Videos: Downloading 132 videos
[download] Downloading video 1 of 132
[youtube] 4OA-SbtiC3M: Downloading webpage
...

Please support alternative channel URLs. Thanks.

[pukkandan]

This is fixed in #245 but the patch never made it to release since blackjack has been inactive for a while. You can check out my fork yt-dlp if you want