Be able to download metadata from DRM protected video

[Luuk3333]

Checklist

• I'm reporting a feature request
• I've verified that I'm running youtube-dl version 2019.11.22
• I've searched the bugtracker for similar feature requests including closed ones

Description

Currently when downloading metadata of a DRM protected video with options like '--write-thumbnail', '--write-info-json' and '--write-description', youtube-dl will show the error 'ERROR: This video is DRM protected' and exit. Even when using the option '--skip-download'.
However, in some situations it would be useful to be able to download video metadata even though the video is protected by DRM.

Here's an example of the current situation:

$ youtube-dl --skip-download --write-thumbnail --write-description "https://www.npostart.nl/binnenstebuiten/20-11-2019/KN_1710420"
[npo] KN_1710420: Downloading token
[npo] KN_1710420: Downloading player JSON
[npo] KN_1710420: Downloading hls profile JSON
[npo] KN_1710420: Downloading dash-widevine profile JSON
[npo] KN_1710420: Downloading dash-playready profile JSON
[npo] KN_1710420: Downloading smooth profile JSON
ERROR: This video is DRM protected.

Relevant options

Using the following options with a DRM protected video will produce the same output as the example above:

• --write-description
• --write-info-json
• --write-annotations
• --write-thumbnail
• --write-all-thumbnails
• --get-url
• --get-title
• --get-id
• --get-thumbnail
• --get-description
• --get-duration
• --get-filename
• --get-format
• --dump-json
• --dump-single-json
• --print-json
• --list-formats
• --write-sub
• --all-subs
• --list-subs

Solution

There are two cases when downloading metadata from a DRM protected video:

• not using the option '--skip-download'
  In this case the error about not being able to download the video due to DRM could be downgraded to a warning, with youtube-dl proceeding to download metadata. However, it may be a good idea to keep the current situation to make it very clear that the video cannot be downloaded.

• using the option '--skip-download'
  In this case the error about not being able to download the video due to DRM should not stop the metadata from being downloaded. The error may be downgraded to a warning or not shown at all.