[outtmpl] Alternate form of format type `l` for `\n` delimited list

README.md

@@ -963,7 +963,7 @@ The field names themselves (the part inside the parenthesis) can also have some
 1. **Date/time Formatting**: Date/time fields can be formatted according to [strftime formatting](https://docs.python.org/3/library/datetime.html#strftime-and-strptime-format-codes) by specifying it separated from the field name using a `>`. Eg: `%(duration>%H-%M-%S)s`, `%(upload_date>%Y-%m-%d)s`, `%(epoch-3600>%H-%M-%S)s`
 1. **Alternatives**: Alternate fields can be specified seperated with a `,`. Eg: `%(release_date>%Y,upload_date>%Y|Unknown)s`
 1. **Default**: A literal default value can be specified for when the field is empty using a `|` seperator. This overrides `--output-na-template`. Eg: `%(uploader|Unknown)s`
-1. **More Conversions**: In addition to the normal format types `diouxXeEfFgGcrs`, `B`, `j`, `l`, `q` can be used for converting to **B**ytes, **j**son, a comma seperated **l**ist and a string **q**uoted for the terminal respectively
+1. **More Conversions**: In addition to the normal format types `diouxXeEfFgGcrs`, `B`, `j`, `l`, `q` can be used for converting to **B**ytes, **j**son, a comma seperated **l**ist (alternate form flag `#` makes it new line `\n` seperated) and a string **q**uoted for the terminal, respectively
 1. **Unicode normalization**: The format type `U` can be used for NFC [unicode normalization](https://docs.python.org/3/library/unicodedata.html#unicodedata.normalize). The alternate form flag (`#`) changes the normalization to NFD and the conversion flag `+` can be used for NFKC/NFKD compatibility equivalence normalization. Eg: `%(title)+.100U` is NFKC
 
 To summarize, the general syntax for a field is:

test/test_YoutubeDL.py

@@ -765,6 +765,7 @@ class TestYoutubeDL(unittest.TestCase):
 
         # Custom type casting
         test('%(formats.:.id)l', 'id1, id2, id3')
+        test('%(formats.:.id)#l', ('id1\nid2\nid3', 'id1 id2 id3'))
         test('%(ext)l', 'mp4')
         test('%(formats.:.id) 15l', '  id1, id2, id3')
         test('%(formats)j', (json.dumps(FORMATS), sanitize(json.dumps(FORMATS))))

yt_dlp/YoutubeDL.py

@@ -1033,7 +1033,8 @@ class YoutubeDL(object):
 
             str_fmt = f'{fmt[:-1]}s'
             if fmt[-1] == 'l':  # list
-                value, fmt = ', '.join(variadic(value)), str_fmt
+                delim = '\n' if '#' in (outer_mobj.group('conversion') or '') else ', '
+                value, fmt = delim.join(variadic(value)), str_fmt
             elif fmt[-1] == 'j':  # json
                 value, fmt = json.dumps(value, default=_dumpjson_default), str_fmt
             elif fmt[-1] == 'q':  # quoted

yt_dlp/utils.py

@@ -2099,7 +2099,9 @@ def sanitize_filename(s, restricted=False, is_id=False):
     def replace_insane(char):
         if restricted and char in ACCENT_CHARS:
             return ACCENT_CHARS[char]
-        if char == '?' or ord(char) < 32 or ord(char) == 127:
+        elif not restricted and char == '\n':
+            return ' '
+        elif char == '?' or ord(char) < 32 or ord(char) == 127:
             return ''
         elif char == '"':
             return '' if restricted else '\''