adding support for cli

youtube_dl/__init__.py

@@ -10,6 +10,7 @@ import io
 import os
 import random
 import sys
+import json
 
 
 from .options import (
@@ -275,7 +276,11 @@ def _real_main(argv=None):
     # source and target containers. From this point the container won't change,
     # so metadata can be added here.
     if opts.addmetadata:
-        postprocessors.append({'key': 'FFmpegMetadata'})
+        postprocessors.append({
+            'key': 'FFmpegMetadata',
+            'preferredinfo': json.load(opts.preferredinfo),
+            })
+
     if opts.convertsubtitles:
         postprocessors.append({
             'key': 'FFmpegSubtitlesConvertor',