The given song must exist, or MPD will abort.  Calling it with an
unknown song is illegal.

Conflicts:
	src/decoder/ffmpeg_decoder_plugin.c

Require libavutil 51.5.0.

This function was added when the libavformat version was 53.2.0, but
the actual release 53.2.0 did not have it.

Use libasound's polling functions, implement a bridge to GSource /
GPollFD and send idle events to clients when an external program
changes the ALSA mixer volume.

Better error handling.

Conflicts:
	src/decoder/ffmpeg_decoder_plugin.c
	src/input/ffmpeg_input_plugin.c

Needed for av_rescale_q() in ffmpeg 0.8.

avcodec_open() has been deprecated.

It's a no-op and deprecated.

URLContext is deprecated.

Support ancient ffmpeg versions.

Keep the device open as long as the output is enabled, but initialize
it only when playback starts.

When we don't have enough data, generate some silence, hoping the
input buffer will fill soon.  Reducing the render buffer size is not
legal.

Blocking inside the render callback is forbidden, and this sleep call
didn't make any sense.

For simpler seeking within current song.

Moving songs using either 'move' or 'moveid' to position -1 (after the
current song) would fail for a song which is just before the current
song.
This patch corrects the check to see if the current song is in the range
to be moved. Since the range is from `start` up to `end` (exclusive) the
check was incorrect, but is now fixed.

This plugin's use of the "Timer" library was wrong; it added the same
amount of virtual data in every iteration in _play(), but did not
actually play something.  This created an artificial, but useless,
delay.  This patch implements the method _cancel(), and implements
hard-coded sleep values.  This is only slightly better, but does not
attempt to look sane.

The implementation of cancel() did not work well: you cannot use
alSourceUnqueueBuffers() to unqueue queued buffers, and our function
openal_unqueue_buffers() left the OpenAL library in a rather undefined
state; nothing was supposed to be queued, but the "filled" variable
was not reset.

The expression "!format" does not make sense, and cannot occur.