Update and correct (format,extension) table for YouTube

diff --git a/youtube-dl b/youtube-dl
index 496ae036fa7c98ed3166e0dfb16e857f4efad409..9fe58a3547e37858ecc3c02482b7bf2c4654be79 100755 (executable)
--- a/youtube-dl
+++ b/youtube-dl
@@ -561,7 +561,8 @@ class YoutubeIE(InfoExtractor):
 
                # Extension
                video_extension = {
-                       '17': '3gp',
+                       '13': '3gp',
+                       '17': 'mp4',
                        '18': 'mp4',
                        '22': 'mp4',
                }.get(format_param, 'flv')