[youtube] Fix n-sig extraction for phone player JS (#2816)

Authored by: MinePlayersPE

test/test_youtube_signature.py

@@ -90,6 +90,10 @@ _NSIG_TESTS = [
         'https://www.youtube.com/s/player/e06dea74/player_ias.vflset/en_US/base.js',
         'AiuodmaDDYw8d3y4bf', 'ankd8eza2T6Qmw',
     ),
+    (
+        'https://www.youtube.com/s/player/5dd88d1d/player-plasma-ias-phone-en_US.vflset/base.js',
+        'kSxKFLeqzv_ZyHSAt', 'n8gS8oRlHOxPFA',
+    ),
 ]
 
 

yt_dlp/extractor/youtube.py

@@ -2413,7 +2413,7 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
 
     def _extract_n_function_name(self, jscode):
         nfunc, idx = self._search_regex(
-            r'\.get\("n"\)\)&&\(b=(?P<nfunc>[a-zA-Z0-9$]{3})(?:\[(?P<idx>\d+)\])?\([a-zA-Z0-9]\)',
+            r'\.get\("n"\)\)&&\(b=(?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 nfunc