Simple lowpass filter implementation.

Originally committed as revision 14921 to svn://svn.ffmpeg.org/ffmpeg/trunk

1 files changed, 83 insertions, 0 deletions

diff --git a/libavcodec/lowpass.h b/libavcodec/lowpass.h
new file mode 100644
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+++ b/libavcodec/lowpass.h
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+/*
+ * Lowpass 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 lowpass.h
+ * lowpass filter interface
+ */
+
+#ifndef FFMPEG_LOWPASS_H
+#define FFMPEG_LOWPASS_H
+
+#include "avcodec.h"
+
+struct FFLPFilterCoeffs;
+struct FFLPFilterState;
+
+/**
+ * Initialize filter coefficients.
+ *
+ * @param order        filter order
+ * @param cutoff_ratio cutoff to input frequency ratio
+ *
+ * @return pointer to filter coefficients structure or NULL if filter cannot be created
+ */
+const struct FFLPFilterCoeffs* ff_lowpass_filter_init_coeffs(int order, float cutoff_ratio);
+
+/**
+ * Create new filter state.
+ *
+ * @param order filter order
+ *
+ * @return pointer to new filter state or NULL if state creation fails
+ */
+struct FFLPFilterState* ff_lowpass_filter_init_state(int order);
+
+#if 0 //enable with arbitrary order filter implementation, use av_free() for filter state only for now
+/**
+ * Free filter coefficients.
+ *
+ * @param coeffs pointer allocated with ff_lowpass_filter_init_coeffs()
+ */
+void ff_lowpass_filter_free_coeffs(struct FFLPFilterCoeffs *coeffs);
+
+/**
+ * Free filter state.
+ *
+ * @param state pointer allocated with ff_lowpass_filter_init_state()
+ */
+void ff_lowpass_filter_free_state(struct FFLPFilterState *state);
+#endif
+
+/**
+ * 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_lowpass_filter(const struct FFLPFilterCoeffs *coeffs, struct FFLPFilterState *state, int size, int16_t *src, int sstep, int16_t *dst, int dstep);
+
+#endif /* FFMPEG_LOWPASS_H */