Opus: playback gain always relative to EBU R128 level (-23db LUFS), must be played 5db louder to match ReplayGain level (-18db LUFS) when using ReplayGain

Submitted by Nikolaus Waxweiler @madig

Link to original bug (#753275)

Description

(not sure if this is the correct place to ask for this)

I use Clementine (GStreamer-based) and ReplayGain all my music. I noticed that while playing around with the new Opus format, those files are played much quieter than music in other formats. After digging around, I found: Opus files are by design always normalized to -23db LUFS (R128), while ReplayGain defaults to -18db LUFS. Foobar2000 seems to simply preamp these files +5db when playing. Could GStreamer do the same? Or maybe take an argument of what reference level to use so players can set and forget it?

(Maybe related: Bug 751534)