Extend documentation for AVOption.

[ffmpeg] / libavcodec / mdct.c

diff --git a/libavcodec/mdct.c b/libavcodec/mdct.c
index 5c3e7b3b19e96caa39acb5732a495f3d88dce0e7..c51f809714417a35f3923203bf9e38a960bc1d81 100644 (file)
--- a/libavcodec/mdct.c
+++ b/libavcodec/mdct.c
@@ -2,18 +2,20 @@
  * MDCT/IMDCT transforms
  * Copyright (c) 2002 Fabrice Bellard.
  *
- * This library is free software; you can redistribute it and/or
+ * 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 of the License, or (at your option) any later version.
+ * version 2.1 of the License, or (at your option) any later version.
  *
- * This library is distributed in the hope that it will be useful,
+ * 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 this library; if not, write to the Free Software
+ * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 #include "dsputil.h"
@@ -23,13 +25,36 @@
  * MDCT/IMDCT transforms.
  */
 
+// Generate a Kaiser-Bessel Derived Window.
+#define BESSEL_I0_ITER 50 // default: 50 iterations of Bessel I0 approximation
+void ff_kbd_window_init(float *window, float alpha, int n)
+{
+   int i, j;
+   double sum = 0.0, bessel, tmp;
+   double local_window[n];
+   double alpha2 = (alpha * M_PI / n) * (alpha * M_PI / n);
+
+   for (i = 0; i < n; i++) {
+       tmp = i * (n - i) * alpha2;
+       bessel = 1.0;
+       for (j = BESSEL_I0_ITER; j > 0; j--)
+           bessel = bessel * tmp / (j * j) + 1;
+       sum += bessel;
+       local_window[i] = sum;
+   }
+
+   sum++;
+   for (i = 0; i < n; i++)
+       window[i] = sqrt(local_window[i] / sum);
+}
+
 /**
  * init MDCT or IMDCT computation.
  */
 int ff_mdct_init(MDCTContext *s, int nbits, int inverse)
 {
     int n, n4, i;
-    float alpha;
+    double alpha;
 
     memset(s, 0, sizeof(*s));
     n = 1 << nbits;
@@ -60,10 +85,10 @@ int ff_mdct_init(MDCTContext *s, int nbits, int inverse)
 /* complex multiplication: p = a * b */
 #define CMUL(pre, pim, are, aim, bre, bim) \
 {\
-    float _are = (are);\
-    float _aim = (aim);\
-    float _bre = (bre);\
-    float _bim = (bim);\
+    double _are = (are);\
+    double _aim = (aim);\
+    double _bre = (bre);\
+    double _bim = (bim);\
     (pre) = _are * _bre - _aim * _bim;\
     (pim) = _are * _bim + _aim * _bre;\
 }