I have an Audio-File in Commons in .ogg. I can download this file as .mp3 from Commons. But I can link this file in Wikibooks.es only as .ogg. But .ogg Files cant be listened to in mobile devices with OS.
It would be nice, when .ogg files in commons can be linkes in Wikipedia and Wikibook as MP3-Files.
(I use some thousand .ogg files from [https://commons.wikimedia.org/wiki/Category:Curso_de_Alem%C3%A1n_Para_Principiantes_con_audio] in [https://es.wikibooks.org/wiki/Curso_de_alem%C3%A1n_para_principiantes_con_audio] )