Hello Devin!

Usually, the lists of allowed extensions is defined in the Storage integrations. For Timeline it looks like:

INSERT INTO `sys_objects_storage` (`object`, `engine`, `params`, `token_life`, `cache_control`, `levels`, `table_files`, `ext_mode`, `ext_allow`, `ext_deny`, `quota_size`, `current_size`, `quota_number`, `current_number`, `max_file_size`, `ts`) VALUES

('bx_timeline_photos', @sStorageEngine, '', 360, 2592000, 3, 'bx_timeline_photos', 'allow-deny', 'jpg,jpeg,jpe,gif,png', '', 0, 0, 0, 0, 0, 0),

('bx_timeline_photos_processed', @sStorageEngine, '', 360, 2592000, 3, 'bx_timeline_photos_processed', 'allow-deny', 'jpg,jpeg,jpe,gif,png', '', 0, 0, 0, 0, 0, 0),

('bx_timeline_videos', @sStorageEngine, '', 360, 2592000, 3, 'bx_timeline_videos', 'allow-deny', 'avi,flv,mpg,mpeg,wmv,mp4,m4v,mov,divx,xvid,3gp,webm,jpg', '', 0, 0, 0, 0, 0, 0),

('bx_timeline_videos_processed', @sStorageEngine, '', 360, 2592000, 3, 'bx_timeline_videos_processed', 'allow-deny', 'avi,flv,mpg,mpeg,wmv,mp4,m4v,mov,divx,xvid,3gp,webm,jpg', '', 0, 0, 0, 0, 0, 0);

But not that adding mp3 to any of this part will not provide the possibility to play files with this extension (need ot write the new processing of it). So you may post them to Files app with the same result.