From 9e38b273b7ac942e7e9fc05a651ed810ab7d30ba Mon Sep 17 00:00:00 2001
From: Simon Sawicki <contact@grub4k.dev>
Date: Thu, 5 Jun 2025 23:50:58 +0200
Subject: [PATCH] [ie/youtube] Rework nsig function name extraction (#13403)

Closes #13401

Authored by: Grub4K
---
 test/test_youtube_signature.py     |  8 ++++++++
 yt_dlp/extractor/youtube/_video.py | 28 ++++++++++++++--------------
 2 files changed, 22 insertions(+), 14 deletions(-)

diff --git a/test/test_youtube_signature.py b/test/test_youtube_signature.py
index 3f777aed7a..3336b6bfff 100644
--- a/test/test_youtube_signature.py
+++ b/test/test_youtube_signature.py
@@ -320,6 +320,14 @@ _NSIG_TESTS = [
         'https://www.youtube.com/s/player/59b252b9/player_ias.vflset/en_US/base.js',
         'D3XWVpYgwhLLKNK4AGX', 'aZrQ1qWJ5yv5h',
     ),
+    (
+        'https://www.youtube.com/s/player/fc2a56a5/player_ias.vflset/en_US/base.js',
+        'qTKWg_Il804jd2kAC', 'OtUAm2W6gyzJjB9u',
+    ),
+    (
+        'https://www.youtube.com/s/player/fc2a56a5/tv-player-ias.vflset/tv-player-ias.js',
+        'qTKWg_Il804jd2kAC', 'OtUAm2W6gyzJjB9u',
+    ),
 ]
 
 
diff --git a/yt_dlp/extractor/youtube/_video.py b/yt_dlp/extractor/youtube/_video.py
index d82225718c..0b53756dc4 100644
--- a/yt_dlp/extractor/youtube/_video.py
+++ b/yt_dlp/extractor/youtube/_video.py
@@ -2229,20 +2229,20 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
     def _extract_n_function_name(self, jscode, player_url=None):
         varname, global_list = self._interpret_player_js_global_var(jscode, player_url)
         if debug_str := traverse_obj(global_list, (lambda _, v: v.endswith('-_w8_'), any)):
-            funcname = self._search_regex(
-                r'''(?xs)
-                    [;\n](?:
-                        (?P<f>function\s+)|
-                        (?:var\s+)?
-                    )(?P<funcname>[a-zA-Z0-9_$]+)\s*(?(f)|=\s*function\s*)
-                    \((?P<argname>[a-zA-Z0-9_$]+)\)\s*\{
-                    (?:(?!\}[;\n]).)+
-                    \}\s*catch\(\s*[a-zA-Z0-9_$]+\s*\)\s*
-                    \{\s*return\s+%s\[%d\]\s*\+\s*(?P=argname)\s*\}\s*return\s+[^}]+\}[;\n]
-                ''' % (re.escape(varname), global_list.index(debug_str)),
-                jscode, 'nsig function name', group='funcname', default=None)
-            if funcname:
-                return funcname
+            pattern = r'''(?x)
+                \{\s*return\s+%s\[%d\]\s*\+\s*(?P<argname>[a-zA-Z0-9_$]+)\s*\}
+            ''' % (re.escape(varname), global_list.index(debug_str))
+            if match := re.search(pattern, jscode):
+                pattern = r'''(?x)
+                    \{\s*\)%s\(\s*
+                    (?:
+                        (?P<funcname_a>[a-zA-Z0-9_$]+)\s*noitcnuf\s*
+                        |noitcnuf\s*=\s*(?P<funcname_b>[a-zA-Z0-9_$]+)(?:\s+rav)?
+                    )[;\n]
+                ''' % re.escape(match.group('argname')[::-1])
+                if match := re.search(pattern, jscode[match.start()::-1]):
+                    a, b = match.group('funcname_a', 'funcname_b')
+                    return (a or b)[::-1]
             self.write_debug(join_nonempty(
                 'Initial search was unable to find nsig function name',
                 player_url and f'        player = {player_url}', delim='\n'), only_once=True)