Allow `images` formats

Necessary for #343.

* They are identified by `vcodec=acodec='none'`
* These formats show as the worst in `-F`
* Any postprocessor that expects audio/video will be skipped
* `b*` and all related selectors will skip such formats
* This commit also does not add any selector for downloading such formats. They have to be explicitly requested by the `format_id`. Implementation of a selector is left for when #389 is resolved

yt_dlp/YoutubeDL.py

@@ -1822,14 +1822,16 @@ class YoutubeDL(object):
                         format_modified = mobj.group('mod') is not None
 
                         format_fallback = not format_type and not format_modified  # for b, w
-                        filter_f = (
+                        _filter_f = (
                             (lambda f: f.get('%scodec' % format_type) != 'none')
                             if format_type and format_modified  # bv*, ba*, wv*, wa*
                             else (lambda f: f.get('%scodec' % not_format_type) == 'none')
                             if format_type  # bv, ba, wv, wa
                             else (lambda f: f.get('vcodec') != 'none' and f.get('acodec') != 'none')
                             if not format_modified  # b, w
-                            else None)  # b*, w*
+                            else lambda f: True)  # b*, w*
+                        filter_f = lambda f: _filter_f(f) and (
+                            f.get('vcodec') != 'none' or f.get('acodec') != 'none')
                     else:
                         filter_f = ((lambda f: f.get('ext') == format_spec)
                                     if format_spec in ['mp4', 'flv', 'webm', '3gp', 'm4a', 'mp3', 'ogg', 'aac', 'wav']  # extension
@@ -2928,6 +2930,8 @@ class YoutubeDL(object):
     @staticmethod
     def format_resolution(format, default='unknown'):
         if format.get('vcodec') == 'none':
+            if format.get('acodec') == 'none':
+                return 'images'
             return 'audio only'
         if format.get('resolution') is not None:
             return format['resolution']

yt_dlp/extractor/common.py

@@ -1473,7 +1473,7 @@ class InfoExtractor(object):
     class FormatSort:
         regex = r' *((?P<reverse>\+)?(?P<field>[a-zA-Z0-9_]+)((?P<separator>[~:])(?P<limit>.*?))?)? *$'
 
-        default = ('hidden', 'hasvid', 'ie_pref', 'lang', 'quality',
+        default = ('hidden', 'aud_or_vid', 'hasvid', 'ie_pref', 'lang', 'quality',
                    'res', 'fps', 'codec:vp9.2', 'size', 'br', 'asr',
                    'proto', 'ext', 'hasaud', 'source', 'format_id')  # These must not be aliases
         ytdl_default = ('hasaud', 'quality', 'tbr', 'filesize', 'vbr',
@@ -1494,6 +1494,9 @@ class InfoExtractor(object):
                      'order': ('m4a', 'aac', 'mp3', 'ogg', 'opus', 'webm', '', 'none'),
                      'order_free': ('opus', 'ogg', 'webm', 'm4a', 'mp3', 'aac', '', 'none')},
             'hidden': {'visible': False, 'forced': True, 'type': 'extractor', 'max': -1000},
+            'aud_or_vid': {'visible': False, 'forced': True, 'type': 'multiple', 'default': 1,
+                           'field': ('vcodec', 'acodec'),
+                           'function': lambda it: int(any(v != 'none' for v in it))},
             'ie_pref': {'priority': True, 'type': 'extractor'},
             'hasvid': {'priority': True, 'field': 'vcodec', 'type': 'boolean', 'not_in_list': ('none',)},
             'hasaud': {'field': 'acodec', 'type': 'boolean', 'not_in_list': ('none',)},
@@ -1701,9 +1704,7 @@ class InfoExtractor(object):
 
                 def wrapped_function(values):
                     values = tuple(filter(lambda x: x is not None, values))
-                    return (self._get_field_setting(field, 'function')(*values) if len(values) > 1
+                    return self._get_field_setting(field, 'function')(values) if values else None
-                            else values[0] if values
-                            else None)
 
                 value = wrapped_function((get_value(f) for f in actual_fields))
             else:
@@ -1719,7 +1720,7 @@ class InfoExtractor(object):
             if not format.get('ext') and 'url' in format:
                 format['ext'] = determine_ext(format['url'])
             if format.get('vcodec') == 'none':
-                format['audio_ext'] = format['ext']
+                format['audio_ext'] = format['ext'] if format.get('acodec') != 'none' else 'none'
                 format['video_ext'] = 'none'
             else:
                 format['video_ext'] = format['ext']

yt_dlp/postprocessor/common.py

@@ -1,5 +1,6 @@
 from __future__ import unicode_literals
 
+import functools
 import os
 
 from ..compat import compat_str
@@ -67,6 +68,25 @@ class PostProcessor(object):
         """Sets the downloader for this PP."""
         self._downloader = downloader
 
+    @staticmethod
+    def _restrict_to(*, video=True, audio=True, images=True):
+        allowed = {'video': video, 'audio': audio, 'images': images}
+
+        def decorator(func):
+            @functools.wraps(func)
+            def wrapper(self, info):
+                format_type = (
+                    'video' if info['vcodec'] != 'none'
+                    else 'audio' if info['acodec'] != 'none'
+                    else 'images')
+                if allowed[format_type]:
+                    func(self, info)
+                else:
+                    self.to_screen('Skipping %s' % format_type)
+                    return [], info
+            return wrapper
+        return decorator
+
     def run(self, information):
         """Run the PostProcessor.
 

yt_dlp/postprocessor/embedthumbnail.py

@@ -16,6 +16,7 @@ try:
 except ImportError:
     has_mutagen = False
 
+from .common import PostProcessor
 from .ffmpeg import (
     FFmpegPostProcessor,
     FFmpegThumbnailsConvertorPP,
@@ -62,6 +63,7 @@ class EmbedThumbnailPP(FFmpegPostProcessor):
     def _report_run(self, exe, filename):
         self.to_screen('%s: Adding thumbnail to "%s"' % (exe, filename))
 
+    @PostProcessor._restrict_to(images=False)
     def run(self, info):
         filename = info['filepath']
         temp_filename = prepend_extension(filename, 'temp')

yt_dlp/postprocessor/ffmpeg.py

@@ -310,6 +310,7 @@ class FFmpegExtractAudioPP(FFmpegPostProcessor):
         except FFmpegPostProcessorError as err:
             raise AudioConversionError(err.msg)
 
+    @PostProcessor._restrict_to(images=False)
     def run(self, information):
         path = information['filepath']
         orig_ext = information['ext']
@@ -419,6 +420,7 @@ class FFmpegVideoConvertorPP(FFmpegPostProcessor):
             return ['-c:v', 'libxvid', '-vtag', 'XVID']
         return []
 
+    @PostProcessor._restrict_to(images=False)
     def run(self, information):
         path, source_ext = information['filepath'], information['ext'].lower()
         target_ext = self._target_ext(source_ext)
@@ -456,6 +458,7 @@ class FFmpegEmbedSubtitlePP(FFmpegPostProcessor):
         super(FFmpegEmbedSubtitlePP, self).__init__(downloader)
         self._already_have_subtitle = already_have_subtitle
 
+    @PostProcessor._restrict_to(images=False)
     def run(self, information):
         if information['ext'] not in ('mp4', 'webm', 'mkv'):
             self.to_screen('Subtitles can only be embedded in mp4, webm or mkv files')
@@ -523,6 +526,7 @@ class FFmpegEmbedSubtitlePP(FFmpegPostProcessor):
 
 
 class FFmpegMetadataPP(FFmpegPostProcessor):
+    @PostProcessor._restrict_to(images=False)
     def run(self, info):
         metadata = {}
 
@@ -625,6 +629,7 @@ class FFmpegMetadataPP(FFmpegPostProcessor):
 
 
 class FFmpegMergerPP(FFmpegPostProcessor):
+    @PostProcessor._restrict_to(images=False)
     def run(self, info):
         filename = info['filepath']
         temp_filename = prepend_extension(filename, 'temp')
@@ -657,6 +662,7 @@ class FFmpegMergerPP(FFmpegPostProcessor):
 
 
 class FFmpegFixupStretchedPP(FFmpegPostProcessor):
+    @PostProcessor._restrict_to(images=False, audio=False)
     def run(self, info):
         stretched_ratio = info.get('stretched_ratio')
         if stretched_ratio is None or stretched_ratio == 1:
@@ -676,6 +682,7 @@ class FFmpegFixupStretchedPP(FFmpegPostProcessor):
 
 
 class FFmpegFixupM4aPP(FFmpegPostProcessor):
+    @PostProcessor._restrict_to(images=False, video=False)
     def run(self, info):
         if info.get('container') != 'm4a_dash':
             return [], info
@@ -694,6 +701,7 @@ class FFmpegFixupM4aPP(FFmpegPostProcessor):
 
 
 class FFmpegFixupM3u8PP(FFmpegPostProcessor):
+    @PostProcessor._restrict_to(images=False)
     def run(self, info):
         filename = info['filepath']
         if self.get_audio_codec(filename) == 'aac':
@@ -805,6 +813,7 @@ class FFmpegSplitChaptersPP(FFmpegPostProcessor):
             ['-ss', compat_str(chapter['start_time']),
              '-t', compat_str(chapter['end_time'] - chapter['start_time'])])
 
+    @PostProcessor._restrict_to(images=False)
     def run(self, info):
         chapters = info.get('chapters') or []
         if not chapters:

yt_dlp/postprocessor/sponskrub.py

@@ -41,6 +41,7 @@ class SponSkrubPP(PostProcessor):
                 return None
         return path
 
+    @PostProcessor._restrict_to(images=False)
     def run(self, information):
         if self.path is None:
             return [], information