When an audio output device is disabled, also disable its mixer.

No caller must ever pass an invalid device number to
mixer_control_setvol() or mixer_control_getvol().

Very small start..

Passing libraries through LDFLAGS is a mistake that causes link to fail
when using --as-needed. Since the ld arguments are positional, so are
libtool's. Use the proper variable, thus, to pass the libraries.

Replaced both player_stop_decoder() invocations with player_dc_stop(),
which also cleans up the pipe.

In the "CANCEL" command handler, the decoder is stopped twice: first
by player_dc_stop(), then by dc_stop().  Remove the latter.

This function was part of a workaround which we don't need anymore.

After adding the container_scan() method the update_regular_file() method was quite hard to read.
Now there's update_container_file() which deals with container files.
That way normal container files (i.e. without embedded tracks) are handled by the old code like a regular file.
This will fix some of the odd behaviour observed.

snd_pcm_writei() returns the type snd_pcm_sframes_t, not int.  Use the
correct variable type.

If the PCM handle gets disconnected, don't close and clear it in
alsa_recover().  The MPD core will call alsa_close() anyway.  This
way, we can always assume that alsa_data.pcm is always valid.

After a seek, wait until enough new chunks are decoded before starting
playback.  If this takes too long, send silence chunks to the audio
outputs meanwhile.

When the audio outputs are closed, also clear the audio format.  If we
don't do this, every call to audio_output_all_update() will open the
device, even if it's meant to be paused.

Don't allow reopening an audio device after pause with
audio_format==NULL, force the caller to provide the audio_format each
time.

When playback is unpaused, pass the audio_format to
audio_output_all_open().  Don't assume that output_all.c remembers the
previous audio format.  Also check if there has been an audio format
yet.

Check audio_output.command after each sub-chunk has been played.  It
discards the rest of the chunk, but since all commands make the device
stop anyway, this is not a problem, but part of the improvement.  This
improves the latency of audio output commands.

When seeking into a new song, and the decoder for the new song fails
to start up, MPD forgot to send the "command_finished" signal to the
main thread.

When pc.next_song is reset due to a decoder failure, also reset the
player.queued flag.  player.queued must not be true when there is no
pc.next_song.

Reset player.xfade and player.buffering from within
player_seek_decoder(), not in the player_process_command() switch
statement.

A larger chunk size means less overhead for managing them.  4 kB seems
to be a reasonable choice: it contains 23 ms of 44.1 kHz 16 bit stereo
data, or 3 ms of 192 kHz 24 bit stereo data.  The original value of
1020 seemed to be too small, there were quite a lot of system calls
and context switches.

The "run_output" program can be used to test an audio output plugin in
an isolated environment.

The music_buffer is a global variable, and must not be freed until the
player thread exits.

Instead of passing individual buffers to audio_output_all_play(), pass
music_chunk objects.  Append all those chunks asynchronously to a
music_pipe instance.  All output threads may then read chunks from
this pipe.  This reduces MPD's internal latency by an order of
magnitude.

When a PAUSE command is received while the decoder starts, don't open
the audio device when the decoder becomes ready.  It's pointless,
because MPD will close if after that.

Moved some more cruft out of do_play().

Moved some cruft out of do_play().

Preparation for the next patch: since the output devices stay open
even when the player thread stops playing, we will need a persistent
music buffer.

audio_output_open() is only called by audio_output_update().  Don't
export it.

When a music chunk is freed (returned to the buffer), poison its
memory.

If the header valgrind/memcheck.h is available, add
VALGRIND_MAKE_MEM_NOACCESS() and VALGRIND_MAKE_MEM_UNDEFINED()
support, which enables nice warnings in the valgrind memory checker.

Memory poisoning is useful for marking memory regions as "undefined".
This poisoning only enabled in the debug build (!NDEBUG).

This is similar to the MPD 0.14 patch "wait 10 seconds before
reopening a failed device", which only covered open() failures.  This
patch adds the same feature for play().