[youtube] Add options to skip webpage and js player for video extraction

[coletdjnz]

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What is the purpose of your pull request?

• (Future?) Bug fix
• Improvement
• New extractor
• New feature

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Description of your pull request and other information

Not sure what to call this.

This code was originally from #682.

This PR adds:

• fallback player url extraction when it fails to be extracted from the webpage
• don't download js player unnecessarily for clients that don't require it
• try extract js player url from any additional client configs
• ability to skip the js player usage/download (inc iframe fallback).
  • This overrides the clients' config setting.
  • This can be enabled with --extractor-args youtube:player_skip=js
  • Formats that require signature decryption will be skipped automatically (since no player url)
• ability to skip the webpage download
  • This can be enabled with --extractor-args youtube:player_skip=webpage

KNOWN ISSUES:

• authentication for multi-channel accounts and multi-account cookies may not work correctly if the webpage (and any additional client configs) are not downloaded.

TODO:

• documentation
• player_skip=js or something else?

[coletdjnz]

Some example usage

1. --extractor-args youtube:player_skip=webpage,configs,js;player_client=android,web
   • This makes extraction solely rely on the API - so no webpage downloads. Might help with avoiding 429s in some situations.
   • Since the web client usually needs the player js, formats from the web client requiring signature decryption will be skipped.
   • 3 initial API requests (android, web, initial data)

2. --extractor-args youtube:player_skip=webpage,configs,js;player_client=android
- Same as above, but without the web client (some minor metadata may be missed - be sure to check)
- 2 initial API requests (android, initial data) Do not use - missing metadata

3. --extractor-args youtube:player_skip=webpage;player_client=android
- since the android client doesn't require the player js, this is the same as 2. Do not use - missing metadata

4. --extractor-args youtube:player_skip=webpage

   • basically forces fallbacks as if the webpage failed to download.
   • player url should be downloaded using the iframe API fallback (once, only if required)

5. --extractor-args youtube:player_skip=webpage;player_client=web_music

   • config webpage for web_music is downloaded (thus player js details), so web formats should work correctly.

Not recommended:

1. --extractor-args youtube:player_skip=webpage,configs,js;player_client=web
   • In some cases you'll get a no formats error (formats from the web client requiring signature decryption will be skipped).
2. --extractor-args youtube:player_skip=js;player_client=web