Remove --filesystem-encoding option

test/test_YoutubeDL.py

@@ -2,6 +2,7 @@
 
 # Allow direct execution
 import os
+import platform
 import sys
 import unittest
 from unittest.mock import patch
@@ -930,11 +931,15 @@ class TestYoutubeDL(unittest.TestCase):
         # --trim-filenames
         test('%(title6)s.%(ext)s', 'あ' * 10 + '.mp4')
         test('%(title6)s.%(ext)s', 'あ' * 3 + '.mp4', trim_file_name='3c')
-        test('%(title6)s.%(ext)s', 'あ' * 3 + '.mp4', trim_file_name='9b', filesystem_encoding='utf-8')
-        test('%(title6)s.%(ext)s', 'あ' * 3 + '.mp4', trim_file_name='10b', filesystem_encoding='utf-8')
-        test('%(title6)s.%(ext)s', 'あ' * 3 + '.mp4', trim_file_name='11b', filesystem_encoding='utf-8')
-        test('%(title6)s.%(ext)s', 'あ' * 4 + '.mp4', trim_file_name='12b', filesystem_encoding='utf-8')
-        test('%(title6)s.%(ext)s', 'あ' * 6 + '.mp4', trim_file_name='12b', filesystem_encoding='utf-16le')
+        if sys.getfilesystemencoding() == 'utf-8' and platform.system() != 'Windows':
+            test('%(title6)s.%(ext)s', 'あ' * 3 + '.mp4', trim_file_name='9b')
+            test('%(title6)s.%(ext)s', 'あ' * 3 + '.mp4', trim_file_name='10b')
+            test('%(title6)s.%(ext)s', 'あ' * 3 + '.mp4', trim_file_name='11b')
+            test('%(title6)s.%(ext)s', 'あ' * 4 + '.mp4', trim_file_name='12b')
+        elif platform.system() == 'Windows':
+            test('%(title6)s.%(ext)s', 'あ' * 4 + '.mp4', trim_file_name='8b')
+            test('%(title6)s.%(ext)s', 'あ' * 4 + '.mp4', trim_file_name='9b')
+            test('%(title6)s.%(ext)s', 'あ' * 5 + '.mp4', trim_file_name='10b')
         test('folder/%(title6)s.%(ext)s', f'fol{os.path.sep}あああ.mp4', trim_file_name='3c')
 
     def test_format_note(self):

yt_dlp/YoutubeDL.py

@@ -13,6 +13,7 @@ import locale
 import operator
 import os
 from pathlib import Path
+import platform
 import random
 import re
 import shutil
@@ -267,7 +268,6 @@ class YoutubeDL:
     outtmpl_na_placeholder: Placeholder for unavailable meta fields.
     restrictfilenames: Do not allow "&" and spaces in file names
     trim_file_name:    Limit length of filename (extension excluded)
-    filesystem_encoding: Encoding to use when calculating filename length in bytes
     windowsfilenames:  True: Force filenames to be Windows compatible
                        False: Sanitize filenames only minimally
                        This option has no effect when running on Windows
@@ -1449,7 +1449,7 @@ class YoutubeDL:
             # no maximum
             return filename + suffix
 
-        encoding = self.params.get('filesystem_encoding') or sys.getfilesystemencoding()
+        encoding = sys.getfilesystemencoding() if platform.system() != 'Windows' else 'utf-16-le'
 
         def trim_filename(name: str):
             if mode == 'b':

yt_dlp/__init__.py

@@ -1,4 +1,3 @@
-import codecs
 import sys
 
 if sys.version_info < (3, 9):
@@ -432,12 +431,6 @@ def validate_options(opts):
     # Other options
     validate_regex('trim filenames', opts.trim_file_name, r'(?:\d+[bc]?|notrim)')
 
-    if opts.filesystem_encoding is not None:
-        try:
-            codecs.lookup(opts.filesystem_encoding)
-        except LookupError:
-            raise ValueError(f'Invalid filesystem encoding: {opts.filesystem_encoding}')
-
     if opts.playlist_items is not None:
         try:
             tuple(PlaylistEntries.parse_playlist_items(opts.playlist_items))
@@ -895,7 +888,6 @@ def parse_options(argv=None):
         'max_downloads': opts.max_downloads,
         'prefer_free_formats': opts.prefer_free_formats,
         'trim_file_name': opts.trim_file_name,
-        'filesystem_encoding': opts.filesystem_encoding,
         'verbose': opts.verbose,
         'dump_intermediate_pages': opts.dump_intermediate_pages,
         'write_pages': opts.write_pages,