[ie/youtube] Add `force_js_variant` extractor-arg

Authored by: bashonly

README.md

@@ -1782,6 +1782,7 @@ The following extractors use this feature:
 * `data_sync_id`: Overrides the account Data Sync ID used in Innertube API requests. This may be needed if you are using an account with `youtube:player_skip=webpage,configs` or `youtubetab:skip=webpage`
 * `visitor_data`: Overrides the Visitor Data used in Innertube API requests. This should be used with `player_skip=webpage,configs` and without cookies. Note: this may have adverse effects if used improperly. If a session from a browser is wanted, you should pass cookies instead (which contain the Visitor ID)
 * `po_token`:  Proof of Origin (PO) Token(s) to use. Comma seperated list of PO Tokens in the format `CLIENT.CONTEXT+PO_TOKEN`, e.g. `youtube:po_token=web.gvs+XXX,web.player=XXX,web_safari.gvs+YYY`. Context can be either `gvs` (Google Video Server URLs) or `player` (Innertube player request)
+* `force_js_variant`: The player javascript variant to use for signature and nsig deciphering. The available clients variants are `base`, `tce`, `tv`, `es6`, `phone`, `tablet`. Only `base` is recommended as a possible workaround; the others are mainly for debugging purposes. The default is to use what is prescribed by the site, and can be selected with `false`
 
 #### youtubetab (YouTube playlists, channels, feeds, etc.)
 * `skip`: One or more of `webpage` (skip initial webpage download), `authcheck` (allow the download of playlists requiring authentication when no initial webpage is downloaded. This may cause unwanted behavior, see [#1122](https://github.com/yt-dlp/yt-dlp/pull/1122) for more details)

yt_dlp/extractor/youtube/_video.py

@@ -1760,6 +1760,15 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
         },
     ]
 
+    _PLAYER_JS_VARIANT_MAP = {
+        'base': '/s/player/{}/player_ias.vflset/en_US/base.js',
+        'tce': '/s/player/{}/player_ias_tce.vflset/en_US/base.js',
+        'tv': '/s/player/{}/tv-player-ias.vflset/tv-player-ias.js',
+        'es6': '/s/player/{}/tv-player-es6.vflset/tv-player-es6.js',
+        'phone': '/s/player/{}/player-plasma-ias-phone-en_US.vflset/base.js',
+        'tablet': '/s/player/{}/player-plasma-ias-tablet-en_US.vflset/base.js',
+    }
+
     @classmethod
     def suitable(cls, url):
         from yt_dlp.utils import parse_qs
@@ -1939,6 +1948,13 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
             get_all=False, expected_type=str)
         if not player_url:
             return
+        js_variant = self._configuration_arg('force_js_variant', [''])[0]
+        if js_variant not in ('false', ''):
+            if js_variant not in self._PLAYER_JS_VARIANT_MAP:
+                raise ExtractorError(f'Invalid JS variant: {js_variant}', expected=True)
+            player_id = self._extract_player_info(player_url)
+            self.write_debug(f'Forcing {js_variant} variant for player {player_id}')
+            player_url = self._PLAYER_JS_VARIANT_MAP[js_variant].format(player_id)
         return urljoin('https://www.youtube.com', player_url)
 
     def _download_player_url(self, video_id, fatal=False):