Flac > ogg, no transcoding

[shinsero]

Hello

I am running subsonic 5.2 beta on a debian server.
Most of my music library includes .FLAC files, so I'm trying to transcode files into .OGG to save some bandwidth (especially on the phone).
Problem is transcoding doesn't seem to work and files are loading without playing in the default subsonic web player or playing directly .FLAC files on the phone (subsonic android app).
My transcoding setup :

Source Destination Step1 Step2
flac oga flac --decode --stdout %s ffmpeg -i - -acodec libvorbis -ab %bk -f ogg -

Can somebody help me ?