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xing_frame.cpp
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xing_frame.cpp
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/*
* mp3chop
*
* (C) 2000-2020 Mike Crowe <[email protected]>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of
* the License, or (at your option) any later version.
*
* This program 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
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
* USA
*/
#include "config.h"
#include "xing_frame.h"
#include <string.h>
inline int ExtractI4(const uint8_t *p)
{
int x;
// big endian extract
x = p[0];
x <<= 8;
x |= p[1];
x <<= 8;
x |= p[2];
x <<= 8;
x |= p[3];
return x;
}
inline void WriteI4(uint8_t *p, int i)
{
*p++ = (i >> 24) & 0xff;
*p++ = (i >> 16) & 0xff;
*p++ = (i >> 8) & 0xff;
*p++ = (i & 0xff);
}
XingFrame::XingFrame()
: flags(0), frame_content(0), frame_content_length(0), frames_pos(0)
{
}
XingFrame::~XingFrame()
{
delete frame_content;
frame_content = 0;
}
bool XingFrame::Read(const uint8_t *begin, const uint8_t *end)
{
int i, head_flags;
int h_id, h_mode, h_sr_index;
static const int sr_table[4] = { 44100, 48000, 32000, 99999 };
// get Xing header data
this->flags = 0; // clear to null incase fail
const uint8_t *buf = begin;
// get selected MPEG header data
h_id = (buf[1] >> 3) & 1;
h_sr_index = (buf[2] >> 2) & 3;
h_mode = (buf[3] >> 6) & 3;
// determine offset of header
if (h_id)
{
// mpeg1
if (h_mode != 3 )
buf+=(32+4);
else
buf+=(17+4);
}
else
{
// mpeg2
if (h_mode != 3)
buf+=(17+4);
else
buf+=(9+4);
}
if (buf[0] != 'X') return 0; // fail
if (buf[1] != 'i') return 0; // header not found
if (buf[2] != 'n') return 0;
if (buf[3] != 'g') return 0;
buf+=4;
this->h_id = h_id;
this->samprate = sr_table[h_sr_index];
if (h_id == 0)
this->samprate >>= 1;
head_flags = this->flags = ExtractI4(buf); buf+=4; // get flags
if (head_flags & FRAMES_FLAG)
{
this->frames_pos = buf - begin;
this->frames = ExtractI4(buf);
buf+=4;
}
if (head_flags & BYTES_FLAG)
{
this->bytes = ExtractI4(buf);
buf+=4;
}
if (head_flags & TOC_FLAG)
{
this->toc_pos = buf - begin;
for(i=0;i<100;i++)
this->toc[i] = buf[i];
buf+=100;
}
this->vbr_scale = -1;
if (head_flags & VBR_SCALE_FLAG)
{
this->vbr_scale = ExtractI4(buf);
buf+=4;
}
delete frame_content;
frame_content = 0;
// Now save it all in frame_content.
frame_content_length = buf - begin;
frame_content = reinterpret_cast<uint8_t *>(operator new(frame_content_length));
memcpy(frame_content, begin, frame_content_length);
return 1; // success
}
void XingFrame::SetFrameCount(int frame_count)
{
WriteI4(frame_content + frames_pos, frame_count);
}
void XingFrame::SetTocEntry(int i, uint8_t v)
{
*(frame_content + toc_pos + i) = v;
}