And make them optional, that way tests don't need to keep creating fake
callbacks if they don't need anything from the audio layer.
Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>
Otherwise we may try to use the gstreamer playbin after destroying it,
leading to various error messages showing up in the console.
Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>
This is better than calling audio_*() functions directly, since we can
make sure signals are wired up properly in glade.
Signed-off-by: Anna Schumaker <Anna@OcarinaProject.net>