[Bug 753275] 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

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=753275

--- Comment #2 from madigens at gmail.com ---
I reported this to Clementine first but was told to report this here. A cursory
look at the source code and a comment tells me that the player sets up this
pipeline: "queue ! audioconvert ! <caps32> ! rgvolume ! rglimiter !
audioconvert2 ! tee [etc.]", grepping the code further doesn't reveal any other
handling of ReplayGain. So any responsibility is shoved off into the rg*
components of GStreamer it seems.

The problem is that GStreamer correctly turns down the volume while playing an
Opus file, but undershoots the mark by 5db. The playback gain header of Opus
files is married to the EBU R128 specification, which means turning down to a
reference level of -23db. RG defaults to -18db. REPLAYGAIN tags like in other
formats are forbidden by the Opus specification, so Opus files need special
treatment by ReplayGain-handlers.

I know nothing of the inner workings of GStreamer, but it seems to me that
rgvolume should catch this and adjust the volume accordingly.

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