Ignore subdomains on reddit URLs

[llyyr]

Make sure you are using the latest version: run youtube-dl --version and ensure your version is 2018.05.09. If it's not, read this FAQ entry and update. Issues with outdated version will be rejected.

• I've verified and I assure that I'm running youtube-dl 2018.05.09

Before submitting an issue make sure you have:

• At least skimmed through the README, most notably the FAQ and BUGS sections
• Searched the bugtracker for similar issues including closed ones
• Checked that provided video/audio/playlist URLs (if any) are alive and playable in a browser

What is the purpose of your issue?

• Bug report (encountered problems with youtube-dl)
• Site support request (request for adding support for a new site)
• Feature request (request for a new functionality)
• Question
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If the purpose of this issue is a site support request please provide all kinds of example URLs support for which should be included (replace following example URLs by yours):

• Single video: https://nm.reddit.com/r/Cricket/comments/8idvby/lousy_cameraman_finds_himself_in_cairns_line_of/

Note that youtube-dl does not support sites dedicated to copyright infringement. In order for site support request to be accepted all provided example URLs should not violate any copyrights.

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Description of your issue, suggested solution and other information

Various subs use dm or nm subdomain which apply different css, there's also np subdomain which does the same. reddit also has a massive number of 2 alphabet subdomains to serve the site in different languages.

youtube-dl already supports www and old, but it's not possible to add support for each and every one of them so it'd be better to ignore it altogether since it doesn't affect reddit detection or .json API availability.

I'll submit a PR if this solution is acceptable.