You need to update 2 filters:

UPDATE `sys_transcoder_filters` 
  SET  `filter_params` =  'a:3:{s:1:"h";s:3:"480";s:10:"force_type";s:3:"mp4";s:14:"ffmpeg_options";a:1:{s:7:"threads";i:0;}}' 
  WHERE `transcoder_object` =  'bx_videos_video_mp4' AND  `filter` =  'Mp4';
UPDATE `sys_transcoder_filters` 
  SET  `filter_params` =  'a:3:{s:1:"h";s:3:"480";s:10:"force_type";s:4:"webm";s:14:"ffmpeg_options";a:1:{s:7:"threads";i:0;}}' 
  WHERE `transcoder_object` =  'bx_videos_video_webm' AND  `filter` =  'Webm';