A mutex acts as a memory barrier, and thus "volatile" is not
necessary.

The Release Track Id uniquely identifies a recording on a release - that
is, even if a recording appears twice on a release (meaning that the
combination of recording and release id are not enough to figure out
which one it is), the release track id will allow differentiating the two.

The tag names are taken from
https://musicbrainz.org/doc/MusicBrainz_Picard/Tags/Mapping

Eliminate the duplicate pa_operation_get_state() call.

The standard has been renamed since the early draft that was
implemented in MPD.

Necessary for "final" on gcc 4.6.

Translate SampleFormat::DSD to SND_PCM_FORMAT_DSD_U8, which was added
to alsa-lib 1.0.27.1.

Enables using range-based "for".

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>

There is no advantage in using g_setenv().

Passing a void pointer is unsafe.

Make it "const".