Add upmix and vdownmix plugins

Added PCM upmix and vdownmix plugins.

The upmix plugin is for upmixing to 4.0 or 5.1 surrounds
by simple copying (and delay line for rear).

The vdownmix plugin is a kind of "virtual surround", which
downmixes 4.0 or 5.1 input to 2.0 output with some effect.

3 files changed, 59 insertions, 1 deletions

diff --git a/doc/Makefile.am b/doc/Makefile.am
index 70bcc3e..dfb40b3 100644
--- a/doc/Makefile.am
+++ b/doc/Makefile.am
@@ -1 +1,2 @@
-EXTRA_DIST = README-pcm-oss README-jack README-polyp
+EXTRA_DIST = README-pcm-oss README-jack README-polyp \
+	upmix.txt vdownmix.txt
diff --git a/doc/upmix.txt b/doc/upmix.txt
new file mode 100644
index 0000000..b8a6da4
--- /dev/null
+++ b/doc/upmix.txt
@@ -0,0 +1,34 @@
+UPMIX PLUGIN
+============
+
+The upmix plugin is an easy-to-use plugin for upmixing from 1 or 2
+channel stream to 4 or 6-channel stream.  The number of channels to be
+expanded is determined by the slave PCM.  For example, the following
+PCM defines upmixing to 5.1 from 2-6 channels input:
+
+	pcm.upmix51 {
+		type upmix
+		slave.pcm "surround51"
+	}
+
+You can use this PCM as a default one by defining below:
+
+	pcm.!default "plug:upmix51"
+
+The upmix plugin copies left and right channels to rear left and right
+with a certain delay.  The delay size can be specified by "delay" PCM
+option in msec.  For example, to set 10ms delay in the above case:
+
+	pcm.upmix51 {
+		type upmix
+		slave.pcm "surround51"
+		channels 6
+		delay 10
+	}
+
+As default, 15ms delay is used.
+
+The center and LFE channels are the average of sum of left and right
+signals.
+
+The accepted format is currently only S16.
diff --git a/doc/vdownmix.txt b/doc/vdownmix.txt
new file mode 100644
index 0000000..0e1403f
--- /dev/null
+++ b/doc/vdownmix.txt
@@ -0,0 +1,23 @@
+VDOWNMIX PLUGIN
+===============
+
+The vdownmix plugin is a downmixer from 4-6 channels to 2-channel
+stereo headphone output.  This plugin processes the input signals with
+a simple spacialization, so the output sounds like a kind of "virtual
+surround".
+
+For example, define the below:
+
+	pcm.!surround51 {
+		type vdownmix
+		slave.pcm "default"
+	}
+	pcm.!surround40 {
+		type vdownmix
+		slave.pcm "default"
+	}
+
+and the outputs from video player to these PCMs are converted to the
+default 2.0 output with a proper downmix.
+
+The accepted format is currently only S16.