Repository: youtube-dl
Issue: HTTP Error 404 but in browser page is valid
Labels: site-support-request

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## Checklist

<!--
Carefully read and work through this check list in order to prevent the most common mistakes and misuse of youtube-dl:
- First of, make sure you are using the latest version of youtube-dl. Run `youtube-dl --version` and ensure your version is 2020.06.06. If it's not, see https://yt-dl.org/update on how to update. Issues with outdated version will be REJECTED.
- Make sure that all provided video/audio/playlist URLs (if any) are alive and playable in a browser.
- Make sure that all URLs and arguments with special characters are properly quoted or escaped as explained in http://yt-dl.org/escape.
- Search the bugtracker for similar issues: http://yt-dl.org/search-issues. DO NOT post duplicates.
- Finally, put x into all relevant boxes (like this [x])
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Version:
I updated using this: sudo curl -L https://yt-dl.org/downloads/latest/youtube-dl -o /usr/local/bin/youtube-dl
and my current version is 2020.05.03 not 2020.06.06 as mentioned. I am on ubuntu 16.04

Also tried adding -u PRIVATE
- [ x] I'm reporting a broken site support
- [ N] I've verified that I'm running youtube-dl version **2020.06.06**
- [ 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


## Verbose log
```
Error:
WARNING: Could not send HEAD request to https://learn.unity.com/tutorial/custom-render-passes-with-lwrp: HTTP Error 404: Not Found
[generic] custom-render-passes-with-lwrp: Downloading webpage
WARNING: Falling back on generic information extractor.
[generic] custom-render-passes-with-lwrp: Extracting information
ERROR: Unsupported URL: https://learn.unity.com/tutorial/custom-render-passes-with-lwrp
Traceback (most recent call last):
  File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 797, in extract_info
    ie_result = ie.extract(url)
  File "/usr/local/bin/youtube-dl/youtube_dl/extractor/common.py", line 530, in extract
    ie_result = self._real_extract(url)
  File "/usr/local/bin/youtube-dl/youtube_dl/extractor/generic.py", line 3370, in _real_extract
    raise UnsupportedError(url)
youtube_dl.utils.UnsupportedError: Unsupported URL: https://learn.unity.com/tutorial/custom-render-passes-with-lwrp

```


## Description

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According to https://ytdl-org.github.io/youtube-dl/supportedsites.html, unity is supported.
I tried the following:
youtube-dl --username <user> --password <pass> --verbose https://learn.unity.com/tutorial/custom-render-passes-with-lwrp

Also tried 
youtube-dl --cookies ./unity.txt --verbose "https://learn.unity.com/tutorial/custom-render-passes-with-lwrp"

Also tried adding -u PRIVATE