[Canvas/VrtNU] relevant URLs give HTTP Error 500

[Moraty]

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Make sure you are using the latest version: run youtube-dl --version and ensure your version is 2018.03.03. 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 Issues with outdated version will be rejected.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 2018.03.03

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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The following sections concretize particular purposed issues, you can erase any section (the contents between triple ---) not applicable to your issue

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Relevant URL (latest episode of the show):
[https://www.vrt.be/vrtnu/a-z/de-ideale-wereld.relevant/]

youtube-dl --username x --password x https://www.vrt.be/vrtnu/a-z/de-ideale-wereld.relevant/
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'-v', u'--username', u'PRIVATE', u'--password', u'PRIVATE', u'https://www.vrt.be/vrtnu/a-z/de-ideale-wereld.relevant/']
[debug] Encodings: locale UTF-8, fs UTF-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2018.03.03
[debug] Python version 2.7.14 (CPython) - Linux-4.13.0-36-generic-x86_64-with-Ubuntu-17.10-artful
[debug] exe versions: ffmpeg 3.3.4-2, ffprobe 3.3.4-2, rtmpdump 2.4
[debug] Proxy map: {}
[VrtNU] Logging in
[VrtNU] Requesting a token
[VrtNU] de-ideale-wereld.relevant: Downloading webpage
[VrtNU] de-ideale-wereld.relevant: Downloading JSON metadata
ERROR: Unable to download JSON metadata: HTTP Error 500: Internal Server Error (caused by HTTPError()); please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; type  youtube-dl -U  to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.

Same, redirected URL:
[https://www.vrt.be/vrtnu/a-z/de-ideale-wereld/2018/de-ideale-wereld-d20180301/]

youtube-dl --username x --password x https://www.vrt.be/vrtnu/a-z/de-ideale-wereld/2018/de-ideale-wereld-d20180301/
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'-v', u'--username', u'PRIVATE', u'--password', u'PRIVATE', u'https://www.vrt.be/vrtnu/a-z/de-ideale-wereld/2018/de-ideale-wereld-d20180301/']
[debug] Encodings: locale UTF-8, fs UTF-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2018.03.03
[debug] Python version 2.7.14 (CPython) - Linux-4.13.0-36-generic-x86_64-with-Ubuntu-17.10-artful
[debug] exe versions: ffmpeg 3.3.4-2, ffprobe 3.3.4-2, rtmpdump 2.4
[debug] Proxy map: {}
[VrtNU] Logging in
[VrtNU] Requesting a token
WARNING: [VrtNU] Authentication failed
[VrtNU] Waiting for 1 seconds before trying again
[VrtNU] Requesting a token
[VrtNU] de-ideale-wereld-d20180301: Downloading webpage
[VrtNU] de-ideale-wereld-d20180301: Downloading JSON metadata
[Canvas] pbs-pub-91102f37-107e-46e0-a11b-47bb6852418c$vid-59f12323-ffeb-4bc4-a62c-cddb5342f6d5: Downloading JSON metadata
[Canvas] pbs-pub-91102f37-107e-46e0-a11b-47bb6852418c$vid-59f12323-ffeb-4bc4-a62c-cddb5342f6d5: Downloading m3u8 information
[Canvas] pbs-pub-91102f37-107e-46e0-a11b-47bb6852418c$vid-59f12323-ffeb-4bc4-a62c-cddb5342f6d5: Downloading MPD manifest
WARNING: [Canvas] Unknown MIME type application/mp4 in DASH manifest
[Canvas] pbs-pub-91102f37-107e-46e0-a11b-47bb6852418c$vid-59f12323-ffeb-4bc4-a62c-cddb5342f6d5: Downloading ISM manifest
[Canvas] pbs-pub-91102f37-107e-46e0-a11b-47bb6852418c$vid-59f12323-ffeb-4bc4-a62c-cddb5342f6d5: Downloading f4m manifest
...
...
<works fine>

Description of your issue, suggested solution and other information

VRTNu/Canvas's relevant URLs redirect to the URL of the latest episode of the show.
Youtube-dl should check if the URL is one of those, and continue with the redirected URL.

Youtube-dl currently tries to build a json-URL by appending ".mssecurevideo.json", but VRTNu/Canvas stopped giving valid responses for relevant URLs.