Repository: yt-dlp/yt-dlp
Issue category: Bug Report

[YouTube] player `3bb1f723`: nsig extraction failed: Some formats may be missing
### DO NOT REMOVE OR SKIP THE ISSUE TEMPLATE

- [X] I understand that I will be **blocked** if I *intentionally* remove or skip any mandatory\* field

### Checklist

- [X] I'm reporting a bug unrelated to a specific site
- [X] I've verified that I have **updated yt-dlp to nightly or master** ([update instructions](https://github.com/yt-dlp/yt-dlp#update-channels))
- [X] I've checked that all provided URLs are playable in a browser with the same IP and same login details
- [X] I've checked that all URLs and arguments with special characters are [properly quoted or escaped](https://github.com/yt-dlp/yt-dlp/wiki/FAQ#video-url-contains-an-ampersand--and-im-getting-some-strange-output-1-2839-or-v-is-not-recognized-as-an-internal-or-external-command)
- [X] I've searched [known issues](https://github.com/yt-dlp/yt-dlp/issues/3766) and the [bugtracker](https://github.com/yt-dlp/yt-dlp/issues?q=) for similar issues **including closed ones**. DO NOT post duplicates
- [X] I've read the [guidelines for opening an issue](https://github.com/yt-dlp/yt-dlp/blob/master/CONTRIBUTING.md#opening-an-issue)

### Provide a description that is worded well enough to be understood

the function _extract_n_function_name of extractor/youtube.py not working with the playerId `3bb1f723`

### Provide verbose output that clearly demonstrates the problem

- [X] Run **your** yt-dlp command with **-vU** flag added (`yt-dlp -vU <your command line>`)
- [ ] If using API, add `'verbose': True` to `YoutubeDL` params instead
- [X] Copy the WHOLE output (starting with `[debug] Command-line config`) and insert it below

### Complete Verbose Output

```shell
[debug] Command-line config: ['https://www.youtube.com/watch?v=2yJgwwDcgV8', '--extractor-args', 'youtube:player_client=mweb', '--no-config', '-v', '-F', '--cookies', 'cookies28.txt']
[debug] Encodings: locale cp1252, fs utf-8, pref cp1252, out utf-8, error utf-8, screen utf-8
[debug] yt-dlp version master@2024.12.04.231213 from yt-dlp/yt-dlp-master-builds [fca3eb5f8] (win_exe)
[debug] Python 3.10.11 (CPython AMD64 64bit) - Windows-10-10.0.22631-SP0 (OpenSSL 1.1.1t  7 Feb 2023)
[debug] exe versions: ffmpeg 7.1-full_build-www.gyan.dev (setts), ffprobe 7.1-full_build-www.gyan.dev, phantomjs 2.5.0, rtmpdump 2.4
[debug] Optional libraries: Cryptodome-3.21.0, brotli-1.1.0, certifi-2024.08.30, curl_cffi-0.5.10, mutagen-1.47.0, requests-2.32.3, sqlite3-3.40.1, urllib3-2.2.3, websockets-14.1
[debug] Proxy map: {}
[debug] Request Handlers: urllib, requests, websockets, curl_cffi
[debug] Loaded 1837 extractors
[youtube] Extracting URL: https://www.youtube.com/watch?v=2yJgwwDcgV8
[youtube] 2yJgwwDcgV8: Downloading webpage
[youtube] 2yJgwwDcgV8: Downloading mweb player API JSON
[youtube] 2yJgwwDcgV8: Downloading player 3bb1f723
WARNING: [youtube] Falling back to generic n function search
         player = https://www.youtube.com/s/player/3bb1f723/player_ias.vflset/en_US/base.js
WARNING: [youtube] 2yJgwwDcgV8: nsig extraction failed: Some formats may be missing
         n = biFW29aV5aoB3znbkq ; player = https://www.youtube.com/s/player/3bb1f723/player_ias.vflset/en_US/base.js
[debug] [youtube] Unable to extract nsig function code (caused by RegexNotFoundError('Unable to extract \x1b[0;94mInitial JS player n function name\x1b[0m; please report this issue on  https://github.com/yt-dlp/yt-dlp/issues?q= , filling out the appropriate issue template. Confirm you are on the latest version using  yt-dlp -U')); please report this issue on  https://github.com/yt-dlp/yt-dlp/issues?q= , filling out the appropriate issue template. Confirm you are on the latest version using  yt-dlp -U
WARNING: [youtube] Falling back to generic n function search
         player = https://www.youtube.com/s/player/3bb1f723/player_ias.vflset/en_US/base.js
WARNING: [youtube] 2yJgwwDcgV8: nsig extraction failed: Some formats may be missing
         n = g_F_AdRs3sNRjsOIzh ; player = https://www.youtube.com/s/player/3bb1f723/player_ias.vflset/en_US/base.js
WARNING: Only images are available for download. use --list-formats to see them
[debug] Sort order given by extractor: quality, res, fps, hdr:12, source, vcodec, channels, acodec, lang, proto
[debug] Formats sorted by: hasvid, ie_pref, quality, res, fps, hdr:12(7), source, vcodec, channels, acodec, lang, proto, size, br, asr, vext, aext, hasaud, id
[info] Available formats for 2yJgwwDcgV8:
ID  EXT   RESOLUTION FPS │ PROTO │ VCODEC MORE INFO
────────────────────────────────────────────────────
sb2 mhtml 48x27        0 │ mhtml │ images storyboard
sb1 mhtml 67x45        1 │ mhtml │ images storyboard
sb0 mhtml 135x90       1 │ mhtml │ images storyboard
```



Functions to edit:
yt_dlp/extractor/youtube.py:YoutubeIE._extract_n_function_name
yt_dlp/extractor/youtube.py:YoutubeIE._extract_n_function_code
yt_dlp/extractor/youtube.py:YoutubeIE._extract_n_function_from_code
Functions added: yt_dlp/extractor/youtube.py:YoutubeIE._fixup_n_function_code

Patch:
diff --git a/yt_dlp/extractor/youtube.py b/yt_dlp/extractor/youtube.py
index 83dde7d9c41f..65cffabb8d83 100644
--- a/yt_dlp/extractor/youtube.py
+++ b/yt_dlp/extractor/youtube.py
@@ -3205,6 +3205,7 @@ def _extract_n_function_name(self, jscode, player_url=None):
         # *  a.D&&(b="nn"[+a.D],c=a.get(b))&&(c=narray[idx](c),a.set(b,c),narray.length||nfunc("")
         # *  a.D&&(PL(a),b=a.j.n||null)&&(b=narray[0](b),a.set("n",b),narray.length||nfunc("")
         # *  a.D&&(b="nn"[+a.D],vL(a),c=a.j[b]||null)&&(c=narray[idx](c),a.set(b,c),narray.length||nfunc("")
+        # *  J.J="";J.url="";J.Z&&(R="nn"[+J.Z],mW(J),N=J.K[R]||null)&&(N=narray[idx](N),J.set(R,N))}};
         funcname, idx = self._search_regex(
             r'''(?x)
             (?:
@@ -3221,7 +3222,7 @@ def _extract_n_function_name(self, jscode, player_url=None):
                     )\)&&\(c=|
                 \b(?P<var>[a-zA-Z0-9_$]+)=
             )(?P<nfunc>[a-zA-Z0-9_$]+)(?:\[(?P<idx>\d+)\])?\([a-zA-Z]\)
-            (?(var),[a-zA-Z0-9_$]+\.set\("n"\,(?P=var)\),(?P=nfunc)\.length)''',
+            (?(var),[a-zA-Z0-9_$]+\.set\((?:"n+"|[a-zA-Z0-9_$]+)\,(?P=var)\))''',
             jscode, 'n function name', group=('nfunc', 'idx'), default=(None, None))
         if not funcname:
             self.report_warning(join_nonempty(
@@ -3230,7 +3231,7 @@ def _extract_n_function_name(self, jscode, player_url=None):
             return self._search_regex(
                 r'''(?xs)
                 ;\s*(?P<name>[a-zA-Z0-9_$]+)\s*=\s*function\([a-zA-Z0-9_$]+\)
-                \s*\{(?:(?!};).)+?["']enhanced_except_''',
+                \s*\{(?:(?!};).)+?return\s*(?P<q>["'])[\w-]+_w8_(?P=q)\s*\+\s*[a-zA-Z0-9_$]+''',
                 jscode, 'Initial JS player n function name', group='name')
         elif not idx:
             return funcname
@@ -3239,6 +3240,11 @@ def _extract_n_function_name(self, jscode, player_url=None):
             rf'var {re.escape(funcname)}\s*=\s*(\[.+?\])\s*[,;]', jscode,
             f'Initial JS player n function list ({funcname}.{idx})')))[int(idx)]
 
+    def _fixup_n_function_code(self, argnames, code):
+        return argnames, re.sub(
+            rf';\s*if\s*\(\s*typeof\s+[a-zA-Z0-9_$]+\s*===?\s*(["\'])undefined\1\s*\)\s*return\s+{argnames[0]};',
+            ';', code)
+
     def _extract_n_function_code(self, video_id, player_url):
         player_id = self._extract_player_info(player_url)
         func_code = self.cache.load('youtube-nsig', player_id, min_ver='2024.07.09')
@@ -3250,7 +3256,8 @@ def _extract_n_function_code(self, video_id, player_url):
 
         func_name = self._extract_n_function_name(jscode, player_url=player_url)
 
-        func_code = jsi.extract_function_code(func_name)
+        # XXX: Workaround for the `typeof` gotcha
+        func_code = self._fixup_n_function_code(*jsi.extract_function_code(func_name))
 
         self.cache.store('youtube-nsig', player_id, func_code)
         return jsi, player_id, func_code
@@ -3266,7 +3273,7 @@ def extract_nsig(s):
             except Exception as e:
                 raise JSInterpreter.Exception(traceback.format_exc(), cause=e)
 
-            if ret.startswith('enhanced_except_'):
+            if ret.startswith('enhanced_except_') or ret.endswith(f'_w8_{s}'):
                 raise JSInterpreter.Exception('Signature function returned an exception')
             return ret
 

Test patch: diff --git a/test/test_youtube_signature.py b/test/test_youtube_signature.py
index 0f7ae34f44f5..1823af378f94 100644
--- a/test/test_youtube_signature.py
+++ b/test/test_youtube_signature.py
@@ -183,6 +183,10 @@
         'https://www.youtube.com/s/player/b12cc44b/player_ias.vflset/en_US/base.js',
         'keLa5R2U00sR9SQK', 'N1OGyujjEwMnLw',
     ),
+    (
+        'https://www.youtube.com/s/player/3bb1f723/player_ias.vflset/en_US/base.js',
+        'gK15nzVyaXE9RsMP3z', 'ZFFWFLPWx9DEgQ',
+    ),
 ]
 
 
@@ -254,8 +258,11 @@ def signature(jscode, sig_input):
 
 
 def n_sig(jscode, sig_input):
-    funcname = YoutubeIE(FakeYDL())._extract_n_function_name(jscode)
-    return JSInterpreter(jscode).call_function(funcname, sig_input)
+    ie = YoutubeIE(FakeYDL())
+    funcname = ie._extract_n_function_name(jscode)
+    jsi = JSInterpreter(jscode)
+    func = jsi.extract_function_from_code(*ie._fixup_n_function_code(*jsi.extract_function_code(funcname)))
+    return func([sig_input])
 
 
 make_sig_test = t_factory(