[FormatSort] Fix `aext` for `--prefer-free-formats`

Closes #4735

README.md

@@ -1530,7 +1530,7 @@ The available fields are:
  - `acodec`: Audio Codec (`flac`/`alac` > `wav`/`aiff` > `opus` > `vorbis` > `aac` > `mp4a` > `mp3` > `eac3` > `ac3` > `dts` > other)
  - `codec`: Equivalent to `vcodec,acodec`
  - `vext`: Video Extension (`mp4` > `webm` > `flv` > other). If `--prefer-free-formats` is used, `webm` is preferred.
- - `aext`: Audio Extension (`m4a` > `aac` > `mp3` > `ogg` > `opus` > `webm` > other). If `--prefer-free-formats` is used, the order changes to `opus` > `ogg` > `webm` > `m4a` > `mp3` > `aac`.
+ - `aext`: Audio Extension (`m4a` > `aac` > `mp3` > `ogg` > `opus` > `webm` > other). If `--prefer-free-formats` is used, the order changes to `ogg` > `opus` > `webm` > `mp3` > `m4a` > `aac`
  - `ext`: Equivalent to `vext,aext`
  - `filesize`: Exact filesize, if known in advance
  - `fs_approx`: Approximate filesize calculated from the manifests

yt_dlp/extractor/common.py

@@ -1693,7 +1693,7 @@ class InfoExtractor:
                      'order_free': ('webm', 'mp4', 'flv', '', 'none')},
             'aext': {'type': 'ordered', 'field': 'audio_ext',
                      'order': ('m4a', 'aac', 'mp3', 'ogg', 'opus', 'webm', '', 'none'),
-                     'order_free': ('opus', 'ogg', 'webm', 'm4a', 'mp3', 'aac', '', 'none')},
+                     'order_free': ('ogg', 'opus', 'webm', 'mp3', 'm4a', 'aac', '', 'none')},
             'hidden': {'visible': False, 'forced': True, 'type': 'extractor', 'max': -1000},
             'aud_or_vid': {'visible': False, 'forced': True, 'type': 'multiple',
                            'field': ('vcodec', 'acodec'),