Add generic IIR filter interface with Butterworth lowpass filter implementation

and remove obsoleted old lowpass filter.

Originally committed as revision 15005 to svn://svn.ffmpeg.org/ffmpeg/trunk

1 files changed, 103 insertions, 0 deletions

diff --git a/libavcodec/iirfilter.h b/libavcodec/iirfilter.h
new file mode 100644
index 0000000000..ac948d8959
--- /dev/null
+++ b/libavcodec/iirfilter.h
@@ -0,0 +1,103 @@
+/*
+ * IIR filter
+ * Copyright (c) 2008 Konstantin Shishkov
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file iirfilter.h
+ * IIR filter interface
+ */
+
+#ifndef FFMPEG_IIRFILTER_H
+#define FFMPEG_IIRFILTER_H
+
+#include "avcodec.h"
+
+struct FFIIRFilterCoeffs;
+struct FFIIRFilterState;
+
+enum IIRFilterType{
+    FF_FILTER_TYPE_BESSEL,
+    FF_FILTER_TYPE_BUTTERWORTH,
+    FF_FILTER_TYPE_CHEBYSHEV,
+    FF_FILTER_TYPE_ELLIPTIC,
+};
+
+enum IIRFilterMode{
+    FF_FILTER_MODE_LOWPASS,
+    FF_FILTER_MODE_HIGHPASS,
+    FF_FILTER_MODE_BANDPASS,
+    FF_FILTER_MODE_BANDSTOP,
+};
+
+/**
+ * Initialize filter coefficients.
+ *
+ * @param filt_type    filter type (e.g. Butterworth)
+ * @param filt_mode    filter mode (e.g. lowpass)
+ * @param order        filter order
+ * @param cutoff_ratio cutoff to input frequency ratio
+ * @param stopband     stopband to input frequency ratio (used by bandpass and bandstop filter modes)
+ * @param ripple       ripple factor (used only in Chebyshev filters)
+ *
+ * @return pointer to filter coefficients structure or NULL if filter cannot be created
+ */
+struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type,
+                                                    enum IIRFilterMode filt_mode,
+                                                    int order, float cutoff_ratio,
+                                                    float stopband, float ripple);
+
+/**
+ * Create new filter state.
+ *
+ * @param order filter order
+ *
+ * @return pointer to new filter state or NULL if state creation fails
+ */
+struct FFIIRFilterState* ff_iir_filter_init_state(int order);
+
+/**
+ * Free filter coefficients.
+ *
+ * @param coeffs pointer allocated with ff_iir_filter_init_coeffs()
+ */
+void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs);
+
+/**
+ * Free filter state.
+ *
+ * @param state pointer allocated with ff_iir_filter_init_state()
+ */
+void ff_iir_filter_free_state(struct FFIIRFilterState *state);
+
+/**
+ * Perform lowpass filtering on input samples.
+ *
+ * @param coeffs pointer to filter coefficients
+ * @param state  pointer to filter state
+ * @param size   input length
+ * @param src    source samples
+ * @param sstep  source stride
+ * @param dst    filtered samples (destination may be the same as input)
+ * @param dstep  destination stride
+ */
+void ff_iir_filter(const struct FFIIRFilterCoeffs *coeffs, struct FFIIRFilterState *state,
+                   int size, const int16_t *src, int sstep, int16_t *dst, int dstep);
+
+#endif /* FFMPEG_IIRFILTER_H */