wsutil/mpeg-audio.c

   1 /* mpeg-audio.c
   2  *
   3  * MPEG Audio header dissection
   4  * Written by Shaun Jackman <sjackman@gmail.com>
   5  * Copyright 2007 Shaun Jackman
   6  *
   7  * Wiretap Library
   8  * SPDX-License-Identifier: GPL-2.0-or-later
   9  */
  10
  11 #include "mpeg-audio.h"
  12
  13 static const int mpa_versions[4] = { 2, -1, 1, 0 };
  14 static const int mpa_layers[4] = { -1, 2, 1, 0 };
  15
  16 static const unsigned int mpa_samples_data[3][3] = {
  17         { 384, 1152, 1152 },
  18         { 384, 1152, 576 },
  19         { 384, 1152, 576 },
  20 };
  21
  22 static const unsigned int mpa_bitrates[3][3][16] = { /* kb/s */
  23         {
  24                 { 0, 32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448 },
  25                 { 0, 32, 48, 56,  64,  80,  96, 112, 128, 160, 192, 224, 256, 320, 384 },
  26                 { 0, 32, 40, 48,  56,  64,  80,  96, 112, 128, 160, 192, 224, 256, 320 },
  27         },
  28         {
  29                 { 0, 32, 48, 56,  64,  80,  96, 112, 128, 144, 160, 176, 192, 224, 256 },
  30                 { 0,  8, 16, 24,  32,  40,  48,  56,  64,  80,  96, 112, 128, 144, 160 },
  31                 { 0,  8, 16, 24,  32,  40,  48,  56,  64,  80,  96, 112, 128, 144, 160 },
  32         },
  33         {
  34                 { 0, 32, 48, 56,  64,  80,  96, 112, 128, 144, 160, 176, 192, 224, 256 },
  35                 { 0,  8, 16, 24,  32,  40,  48,  56,  64,  80,  96, 112, 128, 144, 160 },
  36                 { 0,  8, 16, 24,  32,  40,  48,  56,  64,  80,  96, 112, 128, 144, 160 },
  37         },
  38 };
  39
  40 static const unsigned int mpa_frequencies[3][4] = {
  41         { 44100, 48000, 32000 },
  42         { 22050, 24000, 16000 },
  43         { 11025, 12000, 8000 },
  44 };
  45
  46 static const unsigned int mpa_padding_data[3] = { 4, 1, 1 };
  47
  48 int
  49 mpa_version(const struct mpa *mpa)
  50 {
  51         return mpa_versions[mpa->version];
  52 }
  53
  54 int
  55 mpa_layer(const struct mpa *mpa)
  56 {
  57         return mpa_layers[mpa->layer];
  58 }
  59
  60 unsigned
  61 mpa_samples(const struct mpa *mpa)
  62 {
  63         return mpa_samples_data[mpa_versions[mpa->version]][mpa_layer(mpa)];
  64 }
  65
  66 unsigned
  67 mpa_bitrate(const struct mpa *mpa)
  68 {
  69         return (1000 * (mpa_bitrates[mpa_versions[mpa->version]][mpa_layers[mpa->layer]][mpa->bitrate]));
  70 }
  71
  72 unsigned
  73 mpa_frequency(const struct mpa *mpa)
  74 {
  75         return(mpa_frequencies[mpa_versions[mpa->version]][mpa->frequency]);
  76 }
  77
  78 unsigned
  79 mpa_padding(const struct mpa *mpa)
  80 {
  81         return(mpa->padding ? mpa_padding_data[mpa_layers[mpa->layer]] : 0);
  82 }
  83
  84 /* Decode an ID3v2 synchsafe integer.
  85  * See https://id3.org/id3v2.4.0-structure section 6.2.
  86  */
  87 uint32_t
  88 decode_synchsafe_int(uint32_t input)
  89 {
  90         uint32_t value;
  91
  92         /* High-order byte */
  93         value = (input >> 24) & 0x7f;
  94         /* Shift the result left to make room for the next 7 bits */
  95         value <<= 7;
  96
  97         /* Now OR in the 2nd byte */
  98         value |= (input >> 16) & 0x7f;
  99         value <<= 7;
 100
 101         /* ... and the 3rd */
 102         value |= (input >> 8) & 0x7f;
 103         value <<= 7;
 104
 105         /* For the 4th byte don't do the shift */
 106         value |= input & 0x7f;
 107
 108         return value;
 109 }
 110
 111 /*
 112  * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
 113  *
 114  * Local variables:
 115  * c-basic-offset: 8
 116  * tab-width: 8
 117  * indent-tabs-mode: t
 118  * End:
 119  *
 120  * vi: set shiftwidth=8 tabstop=8 noexpandtab:
 121  * :indentSize=8:tabSize=8:noTabs=false:
 122  */