Introduce --output-na-placeholder (closes #27896)

youtube_dl/YoutubeDL.py

@@ -163,6 +163,7 @@ class YoutubeDL(object):
     simulate:          Do not download the video files.
     format:            Video format code. See options.py for more information.
     outtmpl:           Template for output names.
+    outtmpl_na_placeholder: Placeholder for unavailable meta fields.
     restrictfilenames: Do not allow "&" and spaces in file names
     ignoreerrors:      Do not stop on download errors.
     force_generic_extractor: Force downloader to use the generic extractor
@@ -658,7 +659,7 @@ class YoutubeDL(object):
             template_dict = dict((k, v if isinstance(v, compat_numeric_types) else sanitize(k, v))
                                  for k, v in template_dict.items()
                                  if v is not None and not isinstance(v, (list, tuple, dict)))
-            template_dict = collections.defaultdict(lambda: 'NA', template_dict)
+            template_dict = collections.defaultdict(lambda: self.params.get('outtmpl_na_placeholder', 'NA'), template_dict)
 
             outtmpl = self.params.get('outtmpl', DEFAULT_OUTTMPL)
 
@@ -678,8 +679,8 @@ class YoutubeDL(object):
 
             # Missing numeric fields used together with integer presentation types
             # in format specification will break the argument substitution since
-            # string 'NA' is returned for missing fields. We will patch output
-            # template for missing fields to meet string presentation type.
+            # string NA placeholder is returned for missing fields. We will patch
+            # output template for missing fields to meet string presentation type.
             for numeric_field in self._NUMERIC_FIELDS:
                 if numeric_field not in template_dict:
                     # As of [1] format syntax is:

youtube_dl/__init__.py

@@ -340,6 +340,7 @@ def _real_main(argv=None):
         'format': opts.format,
         'listformats': opts.listformats,
         'outtmpl': outtmpl,
+        'outtmpl_na_placeholder': opts.outtmpl_na_placeholder,
         'autonumber_size': opts.autonumber_size,
         'autonumber_start': opts.autonumber_start,
         'restrictfilenames': opts.restrictfilenames,

youtube_dl/options.py

@@ -689,6 +689,10 @@ def parseOpts(overrideArguments=None):
         '-o', '--output',
         dest='outtmpl', metavar='TEMPLATE',
         help=('Output filename template, see the "OUTPUT TEMPLATE" for all the info'))
+    filesystem.add_option(
+        '--output-na-placeholder',
+        dest='outtmpl_na_placeholder', metavar='PLACEHOLDER', default='NA',
+        help=('Placeholder value for unavailable meta fields in output filename template (default is "%default")'))
     filesystem.add_option(
         '--autonumber-size',
         dest='autonumber_size', metavar='NUMBER', type=int,