Merge branch 'master' of https://github.com/aurium/youtube-dl into aurium-master

youtube_dl/YoutubeDL.py

@@ -262,6 +262,7 @@ class YoutubeDL(object):
     The following options are used by the post processors:
     prefer_ffmpeg:     If True, use ffmpeg instead of avconv if both are available,
                        otherwise prefer avconv.
+    postprocessor_args: Extra parameters for external apps, like avconv.
     """
 
     params = None