+            self.assertEqual(downloaded['format_id'], f1['format_id'])
+
+    def test_audio_only_extractor_format_selection(self):
+        # For extractors with incomplete formats (all formats are audio-only or
+        # video-only) best and worst should fallback to corresponding best/worst
+        # video-only or audio-only formats (as per
+        # https://github.com/rg3/youtube-dl/pull/5556)
+        formats = [
+            {'format_id': 'low', 'ext': 'mp3', 'preference': 1, 'vcodec': 'none', 'url': TEST_URL},
+            {'format_id': 'high', 'ext': 'mp3', 'preference': 2, 'vcodec': 'none', 'url': TEST_URL},
+        ]
+        info_dict = _make_result(formats)
+
+        ydl = YDL({'format': 'best'})
+        ydl.process_ie_result(info_dict.copy())
+        downloaded = ydl.downloaded_info_dicts[0]
+        self.assertEqual(downloaded['format_id'], 'high')
+
+        ydl = YDL({'format': 'worst'})
+        ydl.process_ie_result(info_dict.copy())
+        downloaded = ydl.downloaded_info_dicts[0]
+        self.assertEqual(downloaded['format_id'], 'low')
+
+    def test_format_not_available(self):
+        formats = [
+            {'format_id': 'regular', 'ext': 'mp4', 'height': 360, 'url': TEST_URL},
+            {'format_id': 'video', 'ext': 'mp4', 'height': 720, 'acodec': 'none', 'url': TEST_URL},
+        ]
+        info_dict = _make_result(formats)
+
+        # This must fail since complete video-audio format does not match filter
+        # and extractor does not provide incomplete only formats (i.e. only
+        # video-only or audio-only).
+        ydl = YDL({'format': 'best[height>360]'})
+        self.assertRaises(ExtractorError, ydl.process_ie_result, info_dict.copy())
+
+    def test_format_selection_issue_10083(self):
+        # See https://github.com/rg3/youtube-dl/issues/10083
+        formats = [
+            {'format_id': 'regular', 'height': 360, 'url': TEST_URL},
+            {'format_id': 'video', 'height': 720, 'acodec': 'none', 'url': TEST_URL},
+            {'format_id': 'audio', 'vcodec': 'none', 'url': TEST_URL},
+        ]
+        info_dict = _make_result(formats)
+
+        ydl = YDL({'format': 'best[height>360]/bestvideo[height>360]+bestaudio'})
+        ydl.process_ie_result(info_dict.copy())
+        self.assertEqual(ydl.downloaded_info_dicts[0]['format_id'], 'video+audio')
+
+    def test_invalid_format_specs(self):
+        def assert_syntax_error(format_spec):
+            ydl = YDL({'format': format_spec})
+            info_dict = _make_result([{'format_id': 'foo', 'url': TEST_URL}])
+            self.assertRaises(SyntaxError, ydl.process_ie_result, info_dict)
+
+        assert_syntax_error('bestvideo,,best')
+        assert_syntax_error('+bestaudio')
+        assert_syntax_error('bestvideo+')
+        assert_syntax_error('/')
+
+    def test_format_filtering(self):
+        formats = [
+            {'format_id': 'A', 'filesize': 500, 'width': 1000},
+            {'format_id': 'B', 'filesize': 1000, 'width': 500},
+            {'format_id': 'C', 'filesize': 1000, 'width': 400},
+            {'format_id': 'D', 'filesize': 2000, 'width': 600},
+            {'format_id': 'E', 'filesize': 3000},
+            {'format_id': 'F'},
+            {'format_id': 'G', 'filesize': 1000000},
+        ]
+        for f in formats:
+            f['url'] = 'http://_/'
+            f['ext'] = 'unknown'
+        info_dict = _make_result(formats)
+
+        ydl = YDL({'format': 'best[filesize<3000]'})
+        ydl.process_ie_result(info_dict)
+        downloaded = ydl.downloaded_info_dicts[0]
+        self.assertEqual(downloaded['format_id'], 'D')
+
+        ydl = YDL({'format': 'best[filesize<=3000]'})
+        ydl.process_ie_result(info_dict)
+        downloaded = ydl.downloaded_info_dicts[0]
+        self.assertEqual(downloaded['format_id'], 'E')
+
+        ydl = YDL({'format': 'best[filesize <= ? 3000]'})
+        ydl.process_ie_result(info_dict)
+        downloaded = ydl.downloaded_info_dicts[0]
+        self.assertEqual(downloaded['format_id'], 'F')
+
+        ydl = YDL({'format': 'best [filesize = 1000] [width>450]'})
+        ydl.process_ie_result(info_dict)
+        downloaded = ydl.downloaded_info_dicts[0]
+        self.assertEqual(downloaded['format_id'], 'B')
+
+        ydl = YDL({'format': 'best [filesize = 1000] [width!=450]'})
+        ydl.process_ie_result(info_dict)
+        downloaded = ydl.downloaded_info_dicts[0]
+        self.assertEqual(downloaded['format_id'], 'C')
+
+        ydl = YDL({'format': '[filesize>?1]'})
+        ydl.process_ie_result(info_dict)
+        downloaded = ydl.downloaded_info_dicts[0]
+        self.assertEqual(downloaded['format_id'], 'G')
+
+        ydl = YDL({'format': '[filesize<1M]'})
+        ydl.process_ie_result(info_dict)
+        downloaded = ydl.downloaded_info_dicts[0]
+        self.assertEqual(downloaded['format_id'], 'E')
+
+        ydl = YDL({'format': '[filesize<1MiB]'})
+        ydl.process_ie_result(info_dict)
+        downloaded = ydl.downloaded_info_dicts[0]
+        self.assertEqual(downloaded['format_id'], 'G')
+
+        ydl = YDL({'format': 'all[width>=400][width<=600]'})
+        ydl.process_ie_result(info_dict)
+        downloaded_ids = [info['format_id'] for info in ydl.downloaded_info_dicts]
+        self.assertEqual(downloaded_ids, ['B', 'C', 'D'])
+
+        ydl = YDL({'format': 'best[height<40]'})
+        try:
+            ydl.process_ie_result(info_dict)
+        except ExtractorError:
+            pass
+        self.assertEqual(ydl.downloaded_info_dicts, [])
+
+    def test_default_format_spec(self):
+        ydl = YDL({'simulate': True})
+        self.assertEqual(ydl._default_format_spec({}), 'bestvideo+bestaudio/best')
+
+        ydl = YDL({'is_live': True})
+        self.assertEqual(ydl._default_format_spec({}), 'best/bestvideo+bestaudio')
+
+        ydl = YDL({'simulate': True, 'is_live': True})
+        self.assertEqual(ydl._default_format_spec({}), 'bestvideo+bestaudio/best')
+
+        ydl = YDL({'outtmpl': '-'})
+        self.assertEqual(ydl._default_format_spec({}), 'best/bestvideo+bestaudio')
+
+        ydl = YDL({})
+        self.assertEqual(ydl._default_format_spec({}, download=False), 'bestvideo+bestaudio/best')
+        self.assertEqual(ydl._default_format_spec({'is_live': True}), 'best/bestvideo+bestaudio')
+
+
+class TestYoutubeDL(unittest.TestCase):
+    def test_subtitles(self):
+        def s_formats(lang, autocaption=False):
+            return [{
+                'ext': ext,
+                'url': 'http://localhost/video.%s.%s' % (lang, ext),
+                '_auto': autocaption,
+            } for ext in ['vtt', 'srt', 'ass']]
+        subtitles = dict((l, s_formats(l)) for l in ['en', 'fr', 'es'])
+        auto_captions = dict((l, s_formats(l, True)) for l in ['it', 'pt', 'es'])
+        info_dict = {
+            'id': 'test',
+            'title': 'Test',
+            'url': 'http://localhost/video.mp4',
+            'subtitles': subtitles,
+            'automatic_captions': auto_captions,
+            'extractor': 'TEST',
+        }
+
+        def get_info(params={}):
+            params.setdefault('simulate', True)
+            ydl = YDL(params)
+            ydl.report_warning = lambda *args, **kargs: None
+            return ydl.process_video_result(info_dict, download=False)
+
+        result = get_info()
+        self.assertFalse(result.get('requested_subtitles'))
+        self.assertEqual(result['subtitles'], subtitles)
+        self.assertEqual(result['automatic_captions'], auto_captions)
+
+        result = get_info({'writesubtitles': True})
+        subs = result['requested_subtitles']
+        self.assertTrue(subs)
+        self.assertEqual(set(subs.keys()), set(['en']))
+        self.assertTrue(subs['en'].get('data') is None)
+        self.assertEqual(subs['en']['ext'], 'ass')
+
+        result = get_info({'writesubtitles': True, 'subtitlesformat': 'foo/srt'})
+        subs = result['requested_subtitles']
+        self.assertEqual(subs['en']['ext'], 'srt')
+
+        result = get_info({'writesubtitles': True, 'subtitleslangs': ['es', 'fr', 'it']})
+        subs = result['requested_subtitles']
+        self.assertTrue(subs)
+        self.assertEqual(set(subs.keys()), set(['es', 'fr']))
+
+        result = get_info({'writesubtitles': True, 'writeautomaticsub': True, 'subtitleslangs': ['es', 'pt']})
+        subs = result['requested_subtitles']
+        self.assertTrue(subs)
+        self.assertEqual(set(subs.keys()), set(['es', 'pt']))
+        self.assertFalse(subs['es']['_auto'])
+        self.assertTrue(subs['pt']['_auto'])
+
+        result = get_info({'writeautomaticsub': True, 'subtitleslangs': ['es', 'pt']})
+        subs = result['requested_subtitles']
+        self.assertTrue(subs)
+        self.assertEqual(set(subs.keys()), set(['es', 'pt']))
+        self.assertTrue(subs['es']['_auto'])
+        self.assertTrue(subs['pt']['_auto'])