Fix account index

[dnicolson]

This fixes the YouTube.js account_index option.

It's not clear if this originally worked or not, the most recent review of the extension also indicates the account index option not working.

[terrygonguet]

I added the account_index option for someone who contacted me by email. I never managed to set things up to reproduce it but the option apparently worked for them.

Does this fix something for you that the YouTube.js account_index does not ?

[dnicolson]

I have not been able to get multiple accounts to work with YouTube.js, I made some notes in LuanRT/YouTube.js#735.

I followed the description from LuanRT/YouTube.js#236 and with an extra step (LuanRT/YouTube.js#707 (comment)) but to no avail.

[terrygonguet]

Well, thanks for the effort. Honestly this looks pretty complicated for something we're not sure if it works or even if it's needed 😅

I would be grateful if you could add comments on how this thing works and so we'll have it on hand if we find someone who needs it 👍

[dnicolson]

I think it is needed, the currently used account_index option doesn't seem to work as confirmed by the reviewer.

The window.ytcfg.get('DELEGATED_SESSION_ID') value determines which account is active, it is undefined if it is the primary account.

Data sync IDs identify additional accounts, these come from the /getDatasyncIdsEndpoint endpoint and are saved in local storage.

Adding the X-Goog-PageId header to Innertube requests determines the active account.

Here are examples of local storage data sync ID keys for the number of accounts signed in.

Three accounts:
id_1||id_2::yt-player::yt-player-lv
id_0||::yt-player::yt-player-lv

Two accounts:
id_1||id_0::yt-player::yt-player-lv
id_0||::yt-player::yt-player-lv

One account:
id_0||::yt-player::yt-player-lv