[documentation] Better document `--prefer-free-formats`

Also added `--no-prefer-free-formats`

README.md

@@ -520,8 +520,12 @@ Then simply type this
     --no-audio-multistreams          Only one audio stream is downloaded for
                                      each output file (default)
     --all-formats                    Download all available video formats
-    --prefer-free-formats            Prefer free video formats over non-free
-                                     formats of same quality
+    --prefer-free-formats            Prefer video formats with free containers
+                                     over non-free ones of same quality. Use
+                                     with "-S ext" to strictly prefer free
+                                     containers irrespective of quality
+    --no-prefer-free-formats         Don't give any special preference to free
+                                     containers (default)
     -F, --list-formats               List all available formats of requested
                                      videos
     --list-formats-as-table          Present the output of -F in tabular form

youtube_dlc/extractor/common.py

@@ -1469,13 +1469,12 @@ class InfoExtractor(object):
             elif conversion == 'bytes':
                 return FileDownloader.parse_bytes(value)
             elif conversion == 'order':
-                order_free = self._get_field_setting(field, 'order_free')
-                order_list = order_free if order_free and self._use_free_order else self._get_field_setting(field, 'order')
+                order_list = (self._use_free_order and self._get_field_setting(field, 'order_free')) or self._get_field_setting(field, 'order')
                 use_regex = self._get_field_setting(field, 'regex')
                 list_length = len(order_list)
                 empty_pos = order_list.index('') if '' in order_list else list_length + 1
                 if use_regex and value is not None:
-                    for (i, regex) in enumerate(order_list):
+                    for i, regex in enumerate(order_list):
                         if regex and re.match(regex, value):
                             return list_length - i
                     return list_length - empty_pos  # not in list

youtube_dlc/options.py

@@ -483,7 +483,13 @@ def parseOpts(overrideArguments=None):
     video_format.add_option(
         '--prefer-free-formats',
         action='store_true', dest='prefer_free_formats', default=False,
-        help='Prefer free video formats over non-free formats of same quality')
+        help=(
+            'Prefer video formats with free containers over non-free ones of same quality. '
+            'Use with "-S ext" to strictly prefer free containers irrespective of quality'))
+    video_format.add_option(
+        '--no-prefer-free-formats',
+        action='store_true', dest='prefer_free_formats', default=False,
+        help="Don't give any special preference to free containers (default)")
     video_format.add_option(
         '-F', '--list-formats',
         action='store_true', dest='listformats',