[BBC Sounds] Tracklist Extraction

[garret1317]

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Description of your pull request and other information

This PR adds tracklist extraction for BBC Sounds.
In doing so, it moves the BBC Sounds extraction from BBCCoUkIE to BBCIE, changing the metadata extracted slightly.

I've greatly enjoyed having tracklists extracted as chapters for another radio extractor I've written - it lets me see what's playing without having to use shazam etc, and I can skip past songs I don't like. It also works quite well for skipping news breaks. The BBC Sounds website and app have tracklists available, with full start and end times - but this isn't being extracted.

Looking at the site's HTML, I saw a big JSON blob in window.__PRELOADED_STATE__ with all the programme's metadata, including the tracklist.
Ctrl-F'ing for __PRELOADED_STATE__ in the extractor, I saw that BBCIE had a section that handled this, but it didn't seem to be using it for Sounds. Instead, it was handled by something in BBCCoUkIE.
I didn't see the metadata that I needed available in BBCCoUkIE's network requests, so I removed the sounds/play/ from BBCCoUkIE's _VALID_URL regex.
Now BBCIE handles it with the existing preloaded state code + new tracklist code.

I don't think this breaks any other pages, but I can't be sure as a lot of the URLs in the tests are long gone.
The tests that weren't for dead links didn't seem to be broken by this, at least. (mostly title changes)

The metadata that's extracted has changed. The main changes I noticed were:

• Programme, Episode is now Programme - Episode
• the description is now the long, full length, version
• the station name is extracted as the uploader
• there are a few more formats

So this will doubtless break someone's workflow.

Template

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• At least skimmed through contributing guidelines including yt-dlp coding conventions
• Searched the bugtracker for similar pull requests
• Checked the code with flake8 and ran relevant tests

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What is the purpose of your pull request?

• Fix or improvement to an extractor (Make sure to add/update tests)
• New extractor (Piracy websites will not be accepted)
• Core bug fix/improvement
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Copilot Summary

🤖 Generated by Copilot at f007598

Summary

🎧🔧📜

Improved BBC Sounds extraction and cleaned up BBC code. Added support for BBCIE to handle BBC Sounds URLs and audio chapters, and removed unused code and tests from BBCCoUkIE.

To handle the BBC Sounds links
The BBCIE extractor thinks
It parses the tracklist
For audio chapters to list
And imports some utils for kinks

Walkthrough

• Import join_nonempty and traverse_obj functions from utils.py for string concatenation and nested value access (link, link)
• Remove sounds/play/ pattern from BBCCoUkIE extractor and its test case, since it is now handled by BBCIE extractor (link, link)
• Add a new test case for sounds/play/ URL to BBCIE extractor, demonstrating audio extraction and metadata (link)
• Parse tracklist information from preload_state variable in BBCIE extractor, and assign it as chapters to the audio (link, link)