From 2ad1768c7b48b6c77bbe9c42a4c2744f7b029182 Mon Sep 17 00:00:00 2001
From: Rostislav Pehlivanov <atomnuker@gmail.com>
Date: Sat, 23 Sep 2017 00:38:37 +0100
Subject: opusenc: implement a psychoacoustic system

This commit implements a psychoacoustic system for the native Opus
encoder. Its unlike any other psychoacoustic system known since its
capable of using a lookahead to make better choices on how to treat the
current frame and how many bits to allocate for it (and future frames).

Also, whilst the main bulk of the analysis function has to run in a
single thread, the per-frame anaylsis functions does not modify the main
psychoacoustic context, so in the future it will be fairly trivial to
run those as slice threads.

Signed-off-by: Rostislav Pehlivanov <atomnuker@gmail.com>
---
 libavcodec/opusenc_utils.h | 82 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 82 insertions(+)
 create mode 100644 libavcodec/opusenc_utils.h

(limited to 'libavcodec/opusenc_utils.h')

diff --git a/libavcodec/opusenc_utils.h b/libavcodec/opusenc_utils.h
new file mode 100644
index 0000000000..8b9c5bffaf
--- /dev/null
+++ b/libavcodec/opusenc_utils.h
@@ -0,0 +1,82 @@
+/*
+ * 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
+ */
+
+#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];
+}
-- 
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