[ie/youtube] Fix `n` function name extraction for player `3400486c` (#10542)

Authored by: bashonly

test/test_youtube_signature.py

@@ -171,6 +171,10 @@ _NSIG_TESTS = [
         'https://www.youtube.com/s/player/b22ef6e7/player_ias.vflset/en_US/base.js',
         'b6HcntHGkvBLk_FRf', 'kNPW6A7FyP2l8A',
     ),
+    (
+        'https://www.youtube.com/s/player/3400486c/player_ias.vflset/en_US/base.js',
+        'lL46g3XifCKUZn1Xfw', 'z767lhet6V2Skl',
+    ),
 ]
 
 

yt_dlp/extractor/youtube.py

@@ -3131,7 +3131,14 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
 
     def _extract_n_function_name(self, jscode):
         funcname, idx = self._search_regex(
-            r'''(?x)(?:\.get\("n"\)\)&&\(b=|b=String\.fromCharCode\(110\),c=a\.get\(b\)\)&&\(c=)
+            r'''(?x)
+            (?:
+                \.get\("n"\)\)&&\(b=|
+                (?:
+                    b=String\.fromCharCode\(110\)|
+                    ([a-zA-Z0-9$.]+)&&\(b="nn"\[\+\1\]
+                ),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: