since it's often confused to be the same as `format_note`

* Also fix bug where `_test_url` was being ignored

Ref: https://stackoverflow.com/a/20542029
Related: #340

* Allow skipping a level: `traverse_obj([{k:v1}, {k:v2}], (None, k))` => `[v1, v2]`
* Make keys variadic: `traverse_obj(obj, k1: str, k2: str)` => `traverse_obj(obj, (k1,), (k2,))`
* Fetch from multiple keys: `traverse_obj([{k1:[1], k2:[2], k3:[3]}], (0, (k1, k2), 0))` => `[1, 2]`

TODO: Add tests

* The thumbnail URLs are hard-coded and their actual existence is tested lazily
* Added option `--no-check-formats` to not test them

Closes #340, Related: #402, #337, https://github.com/ytdl-org/youtube-dl/issues/29049

Closes #495

Closes #530

Authored-by: mzbaulhaque 

* Update some `_extract_response` calls to keep them consistent
* Cleanup continuation extraction related code using new API format
* Improve `_extract_account_syncid` to support multiple parameters
* Generalize `get_text` and related functions into one
* Update `INNERTUBE_CONTEXT_CLIENT_NAME` with integer values

Authored by: colethedj

Fixes #522

`SESSION_INDEX` in `ytcfg` is the index of the active account and should be sent as `X-Goog-AuthUser` header

Closes #518
Authored by @colethedj

Authored by: nao20010128nao

* [generic] Extract subtitles in cases missed previously
* [common] Detect discarded subtitles in SMIL manifests
* [generic] Extract everything in the SMIL manifest

Authored by: fstirlitz 

This reverts commit 4d971a16 by @damianoamatruda
Closes #500

This was wrongly checking for `write_thumbnail`

Authored by: colethedj

Authored by: colethedj

Authored by: fstirlitz

Capture the newline character as part of a single-line comment

From #497, Authored by: fstirlitz

From #497, Authored by: fstirlitz

Authored by: colethedj

Authored by colethedj

Closes #477

Related: https://github.com/yt-dlp/yt-dlp/issues/486#issuecomment-877820394

Closes #474

Closes #438, #481, #485 

Authored by: colethedj

Authored by: kevinoconnor7

and some refactoring

Closes #462
Also added extractor-arg `video_types` to `vikichannel`

Co-authored-by: zackmark29, pukkandan

Bug from: 981052c9

:ci skip all

[peertube] only call description endpoint if necessary
https://github.com/ytdl-org/youtube-dl/commit/a8035827177d6b59aca03bd717acb6a9bdd75ada

Authored by: blackjack4494

Authored-by: zenerdi0de