Add samplerate rate converter plugin

Added a rate converter pluging using libsamplerate.
The plugin is built only when libsamplerate is detected by configure.

See doc/samplerate.txt for usage.

This plugin is released under GPL (to follow the license of
libsamplerate), not LGPL.

1 files changed, 30 insertions, 0 deletions

diff --git a/doc/samplerate.txt b/doc/samplerate.txt
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+Rate Converter Plugin Using Libsamplerate
+=========================================
+
+The plugin in rate subdirectory is an external rate converter using
+libsamplerate by Erik de Castro Lopo.  You can use this rate converter
+plugin by defining a rate PCM with "converter" parameter, such as:
+
+	pcm.my_rate {
+		type rate
+		slave.pcm "hw"
+		converter "samplerate"
+	}
+
+The plug plugin has also a similar field, "rate_converter".
+
+Or, more easily, define a global variable "defaults.pcm.rate_converter",
+which is used as the default converter type by plug and rate plugins:
+
+	defaults.pcm.rate_converter "samplerate"
+
+Write the above in your ~/.asoundrc or /etc/asound.conf.
+
+The following converter types are available:
+
+  - samplerate_best	Use SRC_SINC_BEST_QUALITY
+  - samplerate_medium	Use SRC_SINC_MEDIUM_QUALITY
+  - samplerate		Use SRC_SINC_FASTEST
+  - samplerate_order	Use SRC_ZERO_ORDER_HOLD
+  - samplerate_linear	Use SRC_LINEAR
+