FFmpeg
dither.c
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1 /*
2  * Copyright (C) 2012 Michael Niedermayer (michaelni@gmx.at)
3  *
4  * This file is part of libswresample
5  *
6  * libswresample is free software; you can redistribute it and/or
7  * modify it under the terms of the GNU Lesser General Public
8  * License as published by the Free Software Foundation; either
9  * version 2.1 of the License, or (at your option) any later version.
10  *
11  * libswresample is distributed in the hope that it will be useful,
12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14  * Lesser General Public License for more details.
15  *
16  * You should have received a copy of the GNU Lesser General Public
17  * License along with libswresample; if not, write to the Free Software
18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19  */
20 
21 #include "libavutil/avassert.h"
22 #include "swresample_internal.h"
23 
24 void swri_get_dither(SwrContext *s, void *dst, int len, unsigned seed, enum AVSampleFormat out_fmt, enum AVSampleFormat in_fmt) {
25  double scale = 0;
26 #define TMP_EXTRA 2
27  double *tmp = av_malloc((len + TMP_EXTRA) * sizeof(double));
28  int i;
29 
30  out_fmt = av_get_packed_sample_fmt(out_fmt);
31  in_fmt = av_get_packed_sample_fmt( in_fmt);
32 
33  if(in_fmt == AV_SAMPLE_FMT_FLT || in_fmt == AV_SAMPLE_FMT_DBL){
34  if(out_fmt == AV_SAMPLE_FMT_S32) scale = 1.0/(1L<<31);
35  if(out_fmt == AV_SAMPLE_FMT_S16) scale = 1.0/(1L<<15);
36  if(out_fmt == AV_SAMPLE_FMT_U8 ) scale = 1.0/(1L<< 7);
37  }
38  if(in_fmt == AV_SAMPLE_FMT_S32 && out_fmt == AV_SAMPLE_FMT_S16) scale = 1L<<16;
39  if(in_fmt == AV_SAMPLE_FMT_S32 && out_fmt == AV_SAMPLE_FMT_U8 ) scale = 1L<<24;
40  if(in_fmt == AV_SAMPLE_FMT_S16 && out_fmt == AV_SAMPLE_FMT_U8 ) scale = 1L<<8;
41 
42  scale *= s->dither_scale;
43 
44  for(i=0; i<len + TMP_EXTRA; i++){
45  double v;
46  seed = seed* 1664525 + 1013904223;
47 
48  switch(s->dither_method){
49  case SWR_DITHER_RECTANGULAR: v= ((double)seed) / UINT_MAX - 0.5; break;
52  v = ((double)seed) / UINT_MAX;
53  seed = seed*1664525 + 1013904223;
54  v-= ((double)seed) / UINT_MAX;
55  break;
56  default: av_assert0(0);
57  }
58  tmp[i] = v;
59  }
60 
61  for(i=0; i<len; i++){
62  double v;
63 
64  switch(s->dither_method){
67  v = tmp[i];
68  break;
70  v = (- tmp[i] + 2*tmp[i+1] - tmp[i+2]) / sqrt(6);
71  break;
72  default: av_assert0(0);
73  }
74 
75  v*= scale;
76 
77  switch(in_fmt){
78  case AV_SAMPLE_FMT_S16: ((int16_t*)dst)[i] = v; break;
79  case AV_SAMPLE_FMT_S32: ((int32_t*)dst)[i] = v; break;
80  case AV_SAMPLE_FMT_FLT: ((float *)dst)[i] = v; break;
81  case AV_SAMPLE_FMT_DBL: ((double *)dst)[i] = v; break;
82  default: av_assert0(0);
83  }
84  }
85 
86  av_free(tmp);
87 }