Repository: youtube-dl
Issue: Unsupported URL - https://mat6tube.com/watch/-68355713_456239357
Labels: site-support-request,nsfw

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## Checklist

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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 2021.12.17. 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 Issues with outdated version will be REJECTED.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 site you are requesting is not dedicated to copyright infringement, see https://yt-dl.org/copyright-infringement. youtube-dl does not support such sites. In order for site support request to be accepted all provided example URLs should not violate any copyrights.
- Search the bugtracker for similar site support requests: http://yt-dl.org/search-issues. DO NOT post duplicates.
- Finally, put x into all relevant boxes (like this [x])
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- [X] I'm reporting a new site support request
- [X] I've verified that I'm running youtube-dl version **2021.12.17**
- [X] I've checked that all provided URLs are alive and playable in a browser
- [X] I've checked that none of provided URLs violate any copyrights
- [X] I've searched the bugtracker for similar site support requests including closed ones


## Example URLs

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Provide all kinds of example URLs support for which should be included. Replace following example URLs by yours.
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- Single video: https://mat6tube.com/watch/-68355713_456239357
- Playlist: ...?

## Description

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Unable to download videos from: https://mat6tube.com.
```
**youtube-dl -v  -f 'bestvideo[ext=mp4]+bestaudio[ext=m4a]/best[ext=mp4]/best' 'https://mat6tube.com/watch/-68355713_456239357'**
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['-v', '-f', 'bestvideo[ext=mp4]+bestaudio[ext=m4a]/best[ext=mp4]/best', 'https://mat6tube.com/watch/-68355713_456239357']
[debug] Encodings: locale UTF-8, fs utf-8, out utf-8, pref UTF-8
[debug] youtube-dl version 2021.12.17
[debug] Python version 3.10.8 (CPython) - macOS-11.7.1-x86_64-i386-64bit
[debug] exe versions: ffmpeg 5.1.2, ffprobe 5.1.2, rtmpdump 2.4
[debug] Proxy map: {}
[generic] -68355713_456239357: Requesting header
WARNING: Falling back on generic information extractor.
[generic] -68355713_456239357: Downloading webpage
[generic] -68355713_456239357: Extracting information
[debug] Invoking downloader on 'https://mat6tube.com/videofile/-68355713_456239357.mp4'
ERROR: unable to download video data: HTTP Error 404: Not Found
Traceback (most recent call last):
  File "/usr/local/Cellar/youtube-dl/2021.12.17/libexec/lib/python3.10/site-packages/youtube_dl/YoutubeDL.py", line 1976, in process_info
    success = dl(filename, info_dict)
  File "/usr/local/Cellar/youtube-dl/2021.12.17/libexec/lib/python3.10/site-packages/youtube_dl/YoutubeDL.py", line 1915, in dl
    return fd.download(name, info)
  File "/usr/local/Cellar/youtube-dl/2021.12.17/libexec/lib/python3.10/site-packages/youtube_dl/downloader/common.py", line 366, in download
    return self.real_download(filename, info_dict)
  File "/usr/local/Cellar/youtube-dl/2021.12.17/libexec/lib/python3.10/site-packages/youtube_dl/downloader/http.py", line 351, in real_download
    establish_connection()
  File "/usr/local/Cellar/youtube-dl/2021.12.17/libexec/lib/python3.10/site-packages/youtube_dl/downloader/http.py", line 116, in establish_connection
    raise err
  File "/usr/local/Cellar/youtube-dl/2021.12.17/libexec/lib/python3.10/site-packages/youtube_dl/downloader/http.py", line 110, in establish_connection
    ctx.data = self.ydl.urlopen(request)
  File "/usr/local/Cellar/youtube-dl/2021.12.17/libexec/lib/python3.10/site-packages/youtube_dl/YoutubeDL.py", line 2288, in urlopen
    return self._opener.open(req, timeout=self._socket_timeout)
  File "/usr/local/Cellar/python@3.10/3.10.8/Frameworks/Python.framework/Versions/3.10/lib/python3.10/urllib/request.py", line 525, in open
    response = meth(req, response)
  File "/usr/local/Cellar/python@3.10/3.10.8/Frameworks/Python.framework/Versions/3.10/lib/python3.10/urllib/request.py", line 634, in http_response
    response = self.parent.error(
  File "/usr/local/Cellar/python@3.10/3.10.8/Frameworks/Python.framework/Versions/3.10/lib/python3.10/urllib/request.py", line 563, in error
    return self._call_chain(*args)
  File "/usr/local/Cellar/python@3.10/3.10.8/Frameworks/Python.framework/Versions/3.10/lib/python3.10/urllib/request.py", line 496, in _call_chain
    result = func(*args)
  File "/usr/local/Cellar/python@3.10/3.10.8/Frameworks/Python.framework/Versions/3.10/lib/python3.10/urllib/request.py", line 643, in http_error_default
    raise HTTPError(req.full_url, code, msg, hdrs, fp)
urllib.error.HTTPError: HTTP Error 404: Not Found
```