There are code paths (mostly error cases) in which it is possible to
initialize an AudioOutput and then kill it without ever calling
audio_output_new(). In such a case, its destructor will attempt to
free a mixer that was never initialized, leading to an attempt to
take out a lock on a mutex that was similarly never initialized,
which hangs forever.
Fix by always initializing the mixer appropriately.
Pulseaudio expects clients to specify their channel-map if the
default (ALSA) map does not route the audio to the expected speakers.
Many Google results suggest dealing with this by re-routing the audio
channels with the appropriate ALSA plugin, but this will then simply
break any clients which expect the default ALSA mapping.
Virtually all media files and codecs, certainly flac, dca, a52, and of
course anything based on Microsoft's WAVEFORMAT_EXTENSIBLE specification,
assume the layout in the table here:
http://en.wikipedia.org/wiki/Surround_sound#Standard_speaker_channels
Fortunately, pulseaudio directly addresses this with a built-in channel
map for WAVE-EX which can be set automatically in the stream sample-spec.
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
-fixes SIGABRT when mpd is started from a previously paused state
-regression introduced by commit: f5a923b9d1:
'OutputAll: convert to class, move instance to class Partition'
-input_audio_format was previously declared using the static modifier
ensuring it was zero-initialised by default
-the current default-initialised input_audio_format contains garbage at
runtime which allows the AudioFormat.IsDefined() 'fail fast' test in
MultipleOutputs::Update to pass and the SIGABRT follows in
AudioOutput::Open when passed the invalid input_audio_format struct
-switching AudioFormat.IsDefined() for AudioFormat.IsValid() is an
alternative workaround
