pcm/PcmResampler: convert to abstract interface

The PcmResampler interface is implemented by the two classes
FallbackPcmResampler and LibsampleratePcmResampler.  This prepares for
adding more resampler libraries.

src/pcm/LibsamplerateResampler.hxx

@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2003-2013 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_PCM_LIBSAMPLERATE_RESAMPLER_HXX
+#define MPD_PCM_LIBSAMPLERATE_RESAMPLER_HXX
+
+#include "Resampler.hxx"
+#include "PcmBuffer.hxx"
+#include "AudioFormat.hxx"
+
+#include <samplerate.h>
+
+/**
+ * A resampler using libsamplerate.
+ */
+class LibsampleratePcmResampler final : public PcmResampler {
+	unsigned src_rate, dest_rate;
+	unsigned channels;
+
+	SRC_STATE *state;
+	SRC_DATA data;
+
+	PcmBuffer buffer;
+
+public:
+	virtual AudioFormat Open(AudioFormat &af, unsigned new_sample_rate,
+				 Error &error) override;
+	virtual void Close() override;
+	virtual ConstBuffer<void> Resample(ConstBuffer<void> src,
+					   Error &error) override;
+
+private:
+	ConstBuffer<float> Resample2(ConstBuffer<float> src, Error &error);
+};
+
+bool
+pcm_resample_lsr_global_init(const char *converter, Error &error);
+
+#endif