diff --git a/test/test_YoutubeDL.py b/test/test_YoutubeDL.py
index 555a516e6d..e1287f2222 100644
--- a/test/test_YoutubeDL.py
+++ b/test/test_YoutubeDL.py
@@ -13,7 +13,7 @@
 
 from test.helper import FakeYDL, assertRegexpMatches
 from yt_dlp import YoutubeDL
-from yt_dlp.compat import compat_str, compat_urllib_error
+from yt_dlp.compat import compat_os_name, compat_setenv, compat_str, compat_urllib_error
 from yt_dlp.extractor import YoutubeIE
 from yt_dlp.extractor.common import InfoExtractor
 from yt_dlp.postprocessor.common import PostProcessor
@@ -663,7 +663,7 @@ def test(tmpl, expected, *, info=None, **params):
             self.assertEqual(ydl.validate_outtmpl(tmpl), None)
 
             outtmpl, tmpl_dict = ydl.prepare_outtmpl(tmpl, info or self.outtmpl_info)
-            out = outtmpl % tmpl_dict
+            out = ydl.escape_outtmpl(outtmpl) % tmpl_dict
             fname = ydl.prepare_filename(info or self.outtmpl_info)
 
             if callable(expected):
@@ -685,9 +685,15 @@ def test(tmpl, expected, *, info=None, **params):
         test('%(autonumber)s', '001', autonumber_size=3)
 
         # Escaping %
+        test('%', '%')
         test('%%', '%')
         test('%%%%', '%%')
+        test('%s', '%s')
+        test('%%%s', '%%s')
+        test('%d', '%d')
+        test('%abc%', '%abc%')
         test('%%(width)06d.%(ext)s', '%(width)06d.mp4')
+        test('%%%(height)s', '%1080')
         test('%(width)06d.%(ext)s', 'NA.mp4')
         test('%(width)06d.%%(ext)s', 'NA.%(ext)s')
         test('%%(width)06d.%(ext)s', '%(width)06d.mp4')
@@ -702,12 +708,9 @@ def test(tmpl, expected, *, info=None, **params):
         test('%(id)s', ('ab:cd', 'ab -cd'), info={'id': 'ab:cd'})
 
         # Invalid templates
-        self.assertTrue(isinstance(YoutubeDL.validate_outtmpl('%'), ValueError))
         self.assertTrue(isinstance(YoutubeDL.validate_outtmpl('%(title)'), ValueError))
         test('%(invalid@tmpl|def)s', 'none', outtmpl_na_placeholder='none')
         test('%()s', 'NA')
-        test('%s', '%s')
-        test('%d', '%d')
 
         # NA placeholder
         NA_TEST_OUTTMPL = '%(uploader_date)s-%(width)d-%(x|def)s-%(id)s.%(ext)s'
@@ -741,6 +744,7 @@ def test(tmpl, expected, *, info=None, **params):
         # Internal formatting
         FORMATS = self.outtmpl_info['formats']
         test('%(timestamp-1000>%H-%M-%S)s', '11-43-20')
+        test('%(title|%)s %(title|%%)s', '% %%')
         test('%(id+1-height+3)05d', '00158')
         test('%(width+100)05d', 'NA')
         test('%(formats.0) 15s', ('% 15s' % FORMATS[0], '% 15s' % str(FORMATS[0]).replace(':', ' -')))
@@ -759,6 +763,11 @@ def test(tmpl, expected, *, info=None, **params):
         # test('%(foo|)s.%(ext)s', ('.mp4', '_.mp4'))  # fixme
         # test('%(foo|)s', ('', '_'))  # fixme
 
+        # Environment variable expansion for prepare_filename
+        compat_setenv('__yt_dlp_var', 'expanded')
+        envvar = '%__yt_dlp_var%' if compat_os_name == 'nt' else '$__yt_dlp_var'
+        test(envvar, (envvar, 'expanded'))
+
         # Path expansion and escaping
         test('Hello %(title1)s', 'Hello $PATH')
         test('Hello %(title2)s', 'Hello %PATH%')
diff --git a/yt_dlp/YoutubeDL.py b/yt_dlp/YoutubeDL.py
index c0bde43395..3350042c91 100644
--- a/yt_dlp/YoutubeDL.py
+++ b/yt_dlp/YoutubeDL.py
@@ -65,7 +65,8 @@
     float_or_none,
     format_bytes,
     format_field,
-    STR_FORMAT_RE,
+    STR_FORMAT_RE_TMPL,
+    STR_FORMAT_TYPES,
     formatSeconds,
     GeoRestrictedError,
     HEADRequest,
@@ -845,20 +846,40 @@ def get_output_path(self, dir_type='', filename=None):
         return sanitize_path(path, force=self.params.get('windowsfilenames'))
 
     @staticmethod
-    def validate_outtmpl(tmpl):
+    def _outtmpl_expandpath(outtmpl):
+        # expand_path translates '%%' into '%' and '$$' into '$'
+        # correspondingly that is not what we want since we need to keep
+        # '%%' intact for template dict substitution step. Working around
+        # with boundary-alike separator hack.
+        sep = ''.join([random.choice(ascii_letters) for _ in range(32)])
+        outtmpl = outtmpl.replace('%%', '%{0}%'.format(sep)).replace('$$', '${0}$'.format(sep))
+
+        # outtmpl should be expand_path'ed before template dict substitution
+        # because meta fields may contain env variables we don't want to
+        # be expanded. For example, for outtmpl "%(title)s.%(ext)s" and
+        # title "Hello $PATH", we don't want `$PATH` to be expanded.
+        return expand_path(outtmpl).replace(sep, '')
+
+    @staticmethod
+    def escape_outtmpl(outtmpl):
+        ''' Escape any remaining strings like %s, %abc% etc. '''
+        return re.sub(
+            STR_FORMAT_RE_TMPL.format('', '(?![%(\0])'),
+            lambda mobj: ('' if mobj.group('has_key') else '%') + mobj.group(0),
+            outtmpl)
+
+    @classmethod
+    def validate_outtmpl(cls, outtmpl):
         ''' @return None or Exception object '''
+        outtmpl = cls.escape_outtmpl(cls._outtmpl_expandpath(outtmpl))
         try:
-            re.sub(
-                STR_FORMAT_RE.format(''),
-                lambda mobj: ('%' if not mobj.group('has_key') else '') + mobj.group(0),
-                tmpl
-            ) % collections.defaultdict(int)
+            outtmpl % collections.defaultdict(int)
             return None
         except ValueError as err:
             return err
 
     def prepare_outtmpl(self, outtmpl, info_dict, sanitize=None):
-        """ Make the template and info_dict suitable for substitution (outtmpl % info_dict)"""
+        """ Make the template and info_dict suitable for substitution : ydl.outtmpl_escape(outtmpl) % info_dict """
         info_dict = dict(info_dict)
         na = self.params.get('outtmpl_na_placeholder', 'NA')
 
@@ -879,7 +900,7 @@ def prepare_outtmpl(self, outtmpl, info_dict, sanitize=None):
         }
 
         TMPL_DICT = {}
-        EXTERNAL_FORMAT_RE = re.compile(STR_FORMAT_RE.format('[^)]*'))
+        EXTERNAL_FORMAT_RE = re.compile(STR_FORMAT_RE_TMPL.format('[^)]*', f'[{STR_FORMAT_TYPES}]'))
         MATH_FUNCTIONS = {
             '+': float.__add__,
             '-': float.__sub__,
@@ -938,10 +959,11 @@ def get_value(mdict):
 
         def create_key(outer_mobj):
             if not outer_mobj.group('has_key'):
-                return '%{}'.format(outer_mobj.group(0))
+                return f'%{outer_mobj.group(0)}'
 
+            prefix = outer_mobj.group('prefix')
             key = outer_mobj.group('key')
-            fmt = outer_mobj.group('format')
+            original_fmt = fmt = outer_mobj.group('format')
             mobj = re.match(INTERNAL_FORMAT_RE, key)
             if mobj is None:
                 value, default, mobj = None, na, {'fields': ''}
@@ -965,6 +987,7 @@ def create_key(outer_mobj):
                 value = float_or_none(value)
                 if value is None:
                     value, fmt = default, 's'
+
             if sanitize:
                 if fmt[-1] == 'r':
                     # If value is an object, sanitize might convert it to a string
@@ -972,9 +995,10 @@ def create_key(outer_mobj):
                     value, fmt = repr(value), '%ss' % fmt[:-1]
                 if fmt[-1] in 'csr':
                     value = sanitize(mobj['fields'].split('.')[-1], value)
-            key += '\0%s' % fmt
+
+            key = '%s\0%s' % (key.replace('%', '%\0'), original_fmt)
             TMPL_DICT[key] = value
-            return '%({key}){fmt}'.format(key=key, fmt=fmt)
+            return f'{prefix}%({key}){fmt}'
 
         return EXTERNAL_FORMAT_RE.sub(create_key, outtmpl), TMPL_DICT
 
@@ -986,19 +1010,8 @@ def _prepare_filename(self, info_dict, tmpl_type='default'):
                 is_id=(k == 'id' or k.endswith('_id')))
             outtmpl = self.outtmpl_dict.get(tmpl_type, self.outtmpl_dict['default'])
             outtmpl, template_dict = self.prepare_outtmpl(outtmpl, info_dict, sanitize)
-
-            # expand_path translates '%%' into '%' and '$$' into '$'
-            # correspondingly that is not what we want since we need to keep
-            # '%%' intact for template dict substitution step. Working around
-            # with boundary-alike separator hack.
-            sep = ''.join([random.choice(ascii_letters) for _ in range(32)])
-            outtmpl = outtmpl.replace('%%', '%{0}%'.format(sep)).replace('$$', '${0}$'.format(sep))
-
-            # outtmpl should be expand_path'ed before template dict substitution
-            # because meta fields may contain env variables we don't want to
-            # be expanded. For example, for outtmpl "%(title)s.%(ext)s" and
-            # title "Hello $PATH", we don't want `$PATH` to be expanded.
-            filename = expand_path(outtmpl).replace(sep, '') % template_dict
+            outtmpl = self.escape_outtmpl(self._outtmpl_expandpath(outtmpl))
+            filename = outtmpl % template_dict
 
             force_ext = OUTTMPL_TYPES.get(tmpl_type)
             if force_ext is not None:
@@ -2344,7 +2357,7 @@ def print_optional(field):
             if re.match(r'\w+$', tmpl):
                 tmpl = '%({})s'.format(tmpl)
             tmpl, info_copy = self.prepare_outtmpl(tmpl, info_dict)
-            self.to_stdout(tmpl % info_copy)
+            self.to_stdout(self.escape_outtmpl(tmpl) % info_copy)
 
         print_mandatory('title')
         print_mandatory('id')
diff --git a/yt_dlp/postprocessor/execafterdownload.py b/yt_dlp/postprocessor/execafterdownload.py
index 336671d14a..ce77c6e807 100644
--- a/yt_dlp/postprocessor/execafterdownload.py
+++ b/yt_dlp/postprocessor/execafterdownload.py
@@ -23,7 +23,7 @@ def pp_key(cls):
     def parse_cmd(self, cmd, info):
         tmpl, tmpl_dict = self._downloader.prepare_outtmpl(cmd, info)
         if tmpl_dict:  # if there are no replacements, tmpl_dict = {}
-            return tmpl % tmpl_dict
+            return self._downloader.escape_outtmpl(tmpl) % tmpl_dict
 
         # If no replacements are found, replace {} for backard compatibility
         if '{}' not in cmd:
diff --git a/yt_dlp/postprocessor/metadatafromfield.py b/yt_dlp/postprocessor/metadatafromfield.py
index d41ab4bfcf..0027947650 100644
--- a/yt_dlp/postprocessor/metadatafromfield.py
+++ b/yt_dlp/postprocessor/metadatafromfield.py
@@ -55,7 +55,7 @@ def format_to_regex(fmt):
     def run(self, info):
         for dictn in self._data:
             tmpl, tmpl_dict = self._downloader.prepare_outtmpl(dictn['tmpl'], info)
-            data_to_parse = tmpl % tmpl_dict
+            data_to_parse = self._downloader.escape_outtmpl(tmpl) % tmpl_dict
             self.write_debug('Searching for r"%s" in %s' % (dictn['regex'], dictn['tmpl']))
             match = re.search(dictn['regex'], data_to_parse)
             if match is None:
diff --git a/yt_dlp/utils.py b/yt_dlp/utils.py
index 4ff53573f1..2bd0925b6b 100644
--- a/yt_dlp/utils.py
+++ b/yt_dlp/utils.py
@@ -4438,8 +4438,8 @@ def q(qid):
 # As of [1] format syntax is:
 #  %[mapping_key][conversion_flags][minimum_width][.precision][length_modifier]type
 # 1. https://docs.python.org/2/library/stdtypes.html#string-formatting
-STR_FORMAT_RE = r'''(?x)
-    (?<!%)
+STR_FORMAT_RE_TMPL = r'''(?x)
+    (?<!%)(?P<prefix>(?:%%)*)
     %
     (?P<has_key>\((?P<key>{0})\))?  # mapping key
     (?P<format>
@@ -4447,10 +4447,11 @@ def q(qid):
         (?:\d+)?  # minimum field width (optional)
         (?:\.\d+)?  # precision (optional)
         [hlL]?  # length modifier (optional)
-        [diouxXeEfFgGcrs]  # conversion type
+        {1}  # conversion type
     )
 '''
 
+STR_FORMAT_TYPES = 'diouxXeEfFgGcrs'
 
 def limit_length(s, length):
     """ Add ellipses to overly long strings """