[Request] Speed up --get-id on playlists

[SebiderSushi]

Checklist

• I'm reporting a feature request
• I've verified that I'm running youtube-dl version 2019.09.12.1
• I've searched the bugtracker for similar feature requests including closed ones

Description

(I'm not familiar with the internals of youtube-dl, so correct me if i have made any false assumptions)

When running youtube-dl --get-id <playlist url> the process is quite slow - as if youtube-dl downloads and parses the page of every single video to get its id. However, when downloading with a playlist withe the --download-archive option, youtube-dl is able to skip hundreds of videos within just a few seconds total.

At least on sites like youtube.com, where the video id is part of the URL, youtube-dl should already have all video ids after parsing the playlists page. If there are other sites where youtube-dl can already obtain some information (not just limited to video ids) about the individual videos by just parsing the playlist page, it would be great to include them too.

It would be nice if youtube-dl could detect these cases and speed up its process by not downloading a ton of webpages wherever possible.

Ideally, things like the following should be possible in just a few seconds:
youtube-dl --get-filename -o '%(playlist_uploader)s/%(playlist_title)s/%(playlist_index)i_%(id)s.mkv'

[SebiderSushi]

Awesome, thank You very much!

I see now that, on youtube.com, id and title can be used. What about the other fields? Is this extractor dependant? I.e. could they be used even with --flat-playlist as long as the extractor provides them after parsing a playlist page?