-- use software volume when hardware doesn't support all channels (alsa done)
-- paplay needs to set a channel map. our default is only correct for AIFF.
- (we need help from libsndfile for this)
-- silence generation should be moved into the core to avoid races and code
- duplication in the backends
-- examine if it is possible to mimic esd's handling of half duplex cards
- (switch to capture when a recording client connects and drop playback during
- that time)
-- Fix a way for the threading API to handle state and subscription callbacks
- in a nice way.