1 files changed, 87 insertions, 0 deletions
diff --git a/libavcodec/opusenc_utils.h b/libavcodec/opusenc_utils.h
new file mode 100644
index 0000000..be82e13
--- /dev/null
+++ b/libavcodec/opusenc_utils.h
@@ -0,0 +1,87 @@
+/*
+ * Opus encoder
+ * Copyright (c) 2017 Rostislav Pehlivanov <atomnuker@gmail.com>
+ *
+ * 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
+ */
+
+#ifndef AVCODEC_OPUSENC_UTILS_H
+#define AVCODEC_OPUSENC_UTILS_H
+
+#include "opus.h"
+
+typedef struct FFBesselFilter {
+    float a[3];
+    float b[2];
+    float x[3];
+    float y[3];
+} FFBesselFilter;
+
+/* Fills the coefficients, returns 1 if filter will be unstable */
+static inline int bessel_reinit(FFBesselFilter *s, float n, float f0, float fs,
+                                int highpass)
+{
+    int unstable;
+    float c, cfreq, w0, k1, k2;
+
+    if (!highpass) {
+        c = (1.0f/sqrtf(sqrtf(pow(2.0f, 1.0f/n) - 3.0f/4.0f) - 0.5f))/sqrtf(3.0f);
+        cfreq = c*f0/fs;
+        unstable = (cfreq <= 0.0f || cfreq >= 1.0f/4.0f);
+    } else {
+        c = sqrtf(3.0f)*sqrtf(sqrtf(pow(2.0f, 1.0f/n) - 3.0f/4.0f) - 0.5f);
+        cfreq = 0.5f - c*f0/fs;
+        unstable = (cfreq <= 3.0f/8.0f || cfreq >= 1.0f/2.0f);
+    }
+
+    w0 = tanf(M_PI*cfreq);
+    k1 = 3.0f * w0;
+    k2 = 3.0f * w0;
+
+    s->a[0] = k2/(1.0f + k1 + k2);
+    s->a[1] = 2.0f * s->a[0];
+    s->a[2] = s->a[0];
+    s->b[0] = 2.0f * s->a[0] * (1.0f/k2 - 1.0f);
+    s->b[1] = 1.0f - (s->a[0] + s->a[1] + s->a[2] + s->b[0]);
+
+    if (highpass) {
+        s->a[1] *= -1;
+        s->b[0] *= -1;
+    }
+
+    return unstable;
+}
+
+static inline int bessel_init(FFBesselFilter *s, float n, float f0, float fs,
+                              int highpass)
+{
+    memset(s, 0, sizeof(FFBesselFilter));
+    return bessel_reinit(s, n, f0, fs, highpass);
+}
+
+static inline float bessel_filter(FFBesselFilter *s, float x)
+{
+    s->x[2] = s->x[1];
+    s->x[1] = s->x[0];
+    s->x[0] = x;
+    s->y[2] = s->y[1];
+    s->y[1] = s->y[0];
+    s->y[0] = s->a[0]*s->x[0] + s->a[1]*s->x[1] + s->a[2]*s->x[2] + s->b[0]*s->y[1] + s->b[1]*s->y[2];
+    return s->y[0];
+}
+
+#endif /* AVCODEC_OPUSENC_UTILS_H */