Repository: yt-dlp
Issue: Add support for STAGE+ albums
Labels: site-request,account-needed,triage,can-share-account

### DO NOT REMOVE OR SKIP THE ISSUE TEMPLATE

- [X] I understand that I will be **blocked** if I *intentionally* remove or skip any mandatory\* field

### Checklist

- [X] I'm reporting a new site support request
- [X] I've verified that I have **updated yt-dlp to nightly or master** ([update instructions](https://github.com/yt-dlp/yt-dlp#update-channels))
- [X] I've checked that all provided URLs are playable in a browser with the same IP and same login details
- [X] I've checked that none of provided URLs [violate any copyrights](https://github.com/yt-dlp/yt-dlp/blob/master/CONTRIBUTING.md#is-the-website-primarily-used-for-piracy) or contain any [DRM](https://en.wikipedia.org/wiki/Digital_rights_management) to the best of my knowledge
- [X] I've searched [known issues](https://github.com/yt-dlp/yt-dlp/issues/3766) and the [bugtracker](https://github.com/yt-dlp/yt-dlp/issues?q=) for similar issues **including closed ones**. DO NOT post duplicates
- [X] I've read the [guidelines for opening an issue](https://github.com/yt-dlp/yt-dlp/blob/master/CONTRIBUTING.md#opening-an-issue)
- [X] I've read about [sharing account credentials](https://github.com/yt-dlp/yt-dlp/blob/master/CONTRIBUTING.md#are-you-willing-to-share-account-details-if-needed) and am willing to share it if required

### Region

All

### Example URLs

-Album info page: https://www.stage-plus.com/audio/album_85M64TBDBSSJ8D9M
-Audio Player (for chosen track): https://www.stage-plus.com/audio/album_85M64TBDBSSJ8D9M?player=true&trackId=track_AHP62ORBBSOJID9K70SG


### Provide a description that is worded well enough to be understood

This is a register-user-only site for concert performances in the form of VODs and albums, meaning the extractor requires account credentials or cookies. If required, I can provide my username and password.

As of now, support exists for extraction of VODs, but not albums.


### Provide verbose output that clearly demonstrates the problem

- [X] Run **your** yt-dlp command with **-vU** flag added (`yt-dlp -vU <your command line>`)
- [ ] If using API, add `'verbose': True` to `YoutubeDL` params instead
- [X] Copy the WHOLE output (starting with `[debug] Command-line config`) and insert it below

### Complete Verbose Output

```shell
[debug] Command-line config: ['-vU', '-u', 'PRIVATE', '-p', 'PRIVATE', 'https://www.stage-plus.com/audio/album_85M64TBDBSSJ8D9M?player=true&trackId=track_AHP62ORBBSOJID9K70SG']
[debug] Encodings: locale cp1252, fs utf-8, pref cp1252, out utf-8, error utf-8, screen utf-8
[debug] yt-dlp version stable@2024.03.10 from yt-dlp/yt-dlp [615a84447] (win_exe)
[debug] Python 3.8.10 (CPython AMD64 64bit) - Windows-10-10.0.22631-SP0 (OpenSSL 1.1.1k  25 Mar 2021)
[debug] exe versions: ffmpeg 2023-12-07-git-f89cff96d0-full_build-www.gyan.dev (setts), ffprobe 2023-12-07-git-f89cff96d0-full_build-www.gyan.dev
[debug] Optional libraries: Cryptodome-3.20.0, brotli-1.1.0, certifi-2024.02.02, mutagen-1.47.0, requests-2.31.0, sqlite3-3.35.5, urllib3-2.2.1, websockets-12.0
[debug] Proxy map: {}
[debug] Request Handlers: urllib, requests, websockets
[debug] Loaded 1803 extractors
[debug] Fetching release info: https://api.github.com/repos/yt-dlp/yt-dlp/releases/latest
Latest version: stable@2024.03.10 from yt-dlp/yt-dlp
yt-dlp is up to date (stable@2024.03.10 from yt-dlp/yt-dlp)
[generic] Extracting URL: https://www.stage-plus.com/audio/album_85M64TBDBSSJ8D9M?player=true&trackId=track_AHP62ORBBSOJID9K70SG
[generic] album_85M64TBDBSSJ8D9M?player=true&trackId=track_AHP62ORBBSOJID9K70SG: Downloading webpage
WARNING: [generic] Falling back on generic information extractor
[generic] album_85M64TBDBSSJ8D9M?player=true&trackId=track_AHP62ORBBSOJID9K70SG: Extracting information
[debug] Looking for embeds
ERROR: Unsupported URL: https://www.stage-plus.com/audio/album_85M64TBDBSSJ8D9M?player=true&trackId=track_AHP62ORBBSOJID9K70SG
Traceback (most recent call last):
  File "yt_dlp\YoutubeDL.py", line 1594, in wrapper
  File "yt_dlp\YoutubeDL.py", line 1729, in __extract_info
  File "yt_dlp\extractor\common.py", line 732, in extract
  File "yt_dlp\extractor\generic.py", line 2530, in _real_extract
yt_dlp.utils.UnsupportedError: Unsupported URL: https://www.stage-plus.com/audio/album_85M64TBDBSSJ8D9M?player=true&trackId=track_AHP62ORBBSOJID9K70SG
```