Vrai !
J'ai posé la question à ceux qui ne peuvent que savoir, c'est à dire SYNOLOGY, voici leur réponse, en anglais :
Thank you for the feedback. Please allow us to reply in English.
After consulting with our PM team, unfortunately, this format FLAC and OGG hasn't been supported in DS audio yet. However, there is one thing for certain, this suggestion of yours has certainly caught our attention. We have put this suggestion in our enhancement database. If you need to suggest more features, you could also sumit the following form to let the PM team know you ideas:
http://www.synology.com/support/inquiry_form.php?lang=enu&type=1
Hope this helps.
Voilà c'est clair ! A bon entendeur ..