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/* mpeg-audio.c
*
* MPEG Audio header dissection
* Written by Shaun Jackman <sjackman@gmail.com>
* Copyright 2007 Shaun Jackman
*
* Wiretap Library
* SPDX-License-Identifier: GPL-2.0-or-later
*/
#include "mpeg-audio.h"
static const int mpa_versions[4] = { 2, -1, 1, 0 };
static const int mpa_layers[4] = { -1, 2, 1, 0 };
static const unsigned int mpa_samples_data[3][3] = {
{ 384, 1152, 1152 },
{ 384, 1152, 576 },
{ 384, 1152, 576 },
};
static const unsigned int mpa_bitrates[3][3][16] = { /* kb/s */
{
{ 0, 32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448 },
{ 0, 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384 },
{ 0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320 },
},
{
{ 0, 32, 48, 56, 64, 80, 96, 112, 128, 144, 160, 176, 192, 224, 256 },
{ 0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160 },
{ 0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160 },
},
{
{ 0, 32, 48, 56, 64, 80, 96, 112, 128, 144, 160, 176, 192, 224, 256 },
{ 0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160 },
{ 0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160 },
},
};
static const unsigned int mpa_frequencies[3][4] = {
{ 44100, 48000, 32000 },
{ 22050, 24000, 16000 },
{ 11025, 12000, 8000 },
};
static const unsigned int mpa_padding_data[3] = { 4, 1, 1 };
int
mpa_version(const struct mpa *mpa)
{
return mpa_versions[mpa->version];
}
int
mpa_layer(const struct mpa *mpa)
{
return mpa_layers[mpa->layer];
}
unsigned
mpa_samples(const struct mpa *mpa)
{
return mpa_samples_data[mpa_versions[mpa->version]][mpa_layer(mpa)];
}
unsigned
mpa_bitrate(const struct mpa *mpa)
{
return (1000 * (mpa_bitrates[mpa_versions[mpa->version]][mpa_layers[mpa->layer]][mpa->bitrate]));
}
unsigned
mpa_frequency(const struct mpa *mpa)
{
return(mpa_frequencies[mpa_versions[mpa->version]][mpa->frequency]);
}
unsigned
mpa_padding(const struct mpa *mpa)
{
return(mpa->padding ? mpa_padding_data[mpa_layers[mpa->layer]] : 0);
}
/* Decode an ID3v2 synchsafe integer.
* See https://id3.org/id3v2.4.0-structure section 6.2.
*/
uint32_t
decode_synchsafe_int(uint32_t input)
{
uint32_t value;
/* High-order byte */
value = (input >> 24) & 0x7f;
/* Shift the result left to make room for the next 7 bits */
value <<= 7;
/* Now OR in the 2nd byte */
value |= (input >> 16) & 0x7f;
value <<= 7;
/* ... and the 3rd */
value |= (input >> 8) & 0x7f;
value <<= 7;
/* For the 4th byte don't do the shift */
value |= input & 0x7f;
return value;
}
/*
* Editor modelines - https://www.wireshark.org/tools/modelines.html
*
* Local variables:
* c-basic-offset: 8
* tab-width: 8
* indent-tabs-mode: t
* End:
*
* vi: set shiftwidth=8 tabstop=8 noexpandtab:
* :indentSize=8:tabSize=8:noTabs=false:
*/
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