[ie/youtube] Fix JS `n` function name extraction (#10390)

Fixes nsig decoding for player b22ef6e7

Closes #10391
Authored by: bashonly, seproDev

Co-authored-by: sepro <4618135+seproDev@users.noreply.github.com>

test/test_youtube_signature.py

@@ -167,6 +167,10 @@ _NSIG_TESTS = [
         'https://www.youtube.com/s/player/590f65a6/player_ias.vflset/en_US/base.js',
         '1tm7-g_A9zsI8_Lay_', 'xI4Vem4Put_rOg',
     ),
+    (
+        'https://www.youtube.com/s/player/b22ef6e7/player_ias.vflset/en_US/base.js',
+        'b6HcntHGkvBLk_FRf', 'kNPW6A7FyP2l8A',
+    ),
 ]
 
 

yt_dlp/extractor/youtube.py

@@ -3130,7 +3130,8 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
 
     def _extract_n_function_name(self, jscode):
         funcname, idx = self._search_regex(
-            r'\.get\("n"\)\)&&\(b=(?P<nfunc>[a-zA-Z0-9$]+)(?:\[(?P<idx>\d+)\])?\([a-zA-Z0-9]\)',
+            r'''(?x)(?:\.get\("n"\)\)&&\(b=|b=String\.fromCharCode\(110\),c=a\.get\(b\)\)&&\(c=)
+            (?P<nfunc>[a-zA-Z0-9$]+)(?:\[(?P<idx>\d+)\])?\([a-zA-Z0-9]\)''',
             jscode, 'Initial JS player n function name', group=('nfunc', 'idx'))
         if not idx:
             return funcname