[youtube] convert subtitles with --skip-download

youtube_dlc/YoutubeDL.py

@@ -105,6 +105,7 @@
     FFmpegFixupStretchedPP,
     FFmpegMergerPP,
     FFmpegPostProcessor,
+    FFmpegSubtitlesConvertorPP,
     get_postprocessor,
 )
 from .version import __version__
@@ -1846,6 +1847,29 @@ def dl(name, info):
                                                 (sub_lang, error_to_compat_str(err)))
                             continue
 
+        if self.params.get('skip_download', False):
+            if self.params.get('convertsubtitles', False):
+                subconv = FFmpegSubtitlesConvertorPP(self, format=self.params.get('convertsubtitles'))
+                filename_real_ext = os.path.splitext(filename)[1][1:]
+                filename_wo_ext = (
+                    os.path.splitext(filename)[0]
+                    if filename_real_ext == info_dict['ext']
+                    else filename)
+                afilename = '%s.%s' % (filename_wo_ext, self.params.get('convertsubtitles'))
+                if subconv.available:
+                    info_dict.setdefault('__postprocessors', [])
+                    # info_dict['__postprocessors'].append(subconv)
+                if os.path.exists(encodeFilename(afilename)):
+                        self.to_screen(
+                            '[download] %s has already been downloaded and '
+                            'converted' % afilename)
+                else:
+                    try:
+                        self.post_process(filename, info_dict)
+                    except (PostProcessingError) as err:
+                        self.report_error('postprocessing: %s' % str(err))
+                        return
+
         if self.params.get('writeinfojson', False):
             infofn = replace_extension(filename, 'info.json', info_dict.get('ext'))
             if self.params.get('nooverwrites', False) and os.path.exists(encodeFilename(infofn)):

youtube_dlc/__init__.py

@@ -315,6 +315,7 @@ def parse_retries(retries):
         else match_filter_func(opts.match_filter))
 
     ydl_opts = {
+        'convertsubtitles': opts.convertsubtitles,
         'usenetrc': opts.usenetrc,
         'username': opts.username,
         'password': opts.password,