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/*
* TwoLAME: an optimized MPEG Audio Layer Two encoder
*
* Copyright (C) 2001-2004 Michael Cheng
* Copyright (C) 2004-2006 The TwoLAME Project
*
* This library 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 2.1 of the License, or (at your option) any later version.
*
* This library 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
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
* $Id$
*
*/
#include <stdio.h>
#include <stdlib.h>
#include "twolame.h"
#include "common.h"
#include "bitbuffer.h"
#include "energy.h"
// Returns the desired number of ancillary bits to be
// reserved at the end of the frame
int get_required_energy_bits(twolame_options * glopts)
{
if (glopts->mode == TWOLAME_MONO) {
// only 2 bytes + zero at n-3 needed for energy level for mono channel
return 24;
} else {
// 5 bytes for the stereo energy info
return 40;
}
}
// Calculates the energy levels of current frame and
// inserts it into the end of the frame
void do_energy_levels(twolame_options * glopts, bit_stream * bs)
{
/* Reference: Using the BWF Energy Levels in AudioScience Bitstreams
http://www.audioscience.com/internet/download/notes/note0001_MPEG_energy.pdf
Specification of the Broadcast Wave Format: Supplement 1 - MPEG audio
http://www.ebu.ch/CMSimages/en/tec_doc_t3285_s1_tcm6-10545.pdf
http://www.sr.se/utveckling/tu/bwf/
The absolute peak of the PCM file for the left and right channel in this frame are written
into the last 5 bytes of the frame.
The last 5 bytes *must* be reserved for this to work correctly (otherwise you'll be
overwriting mpeg audio data) */
short int *leftpcm = glopts->buffer[0];
short int *rightpcm = glopts->buffer[1];
int i, leftMax, rightMax;
unsigned char rhibyte, rlobyte, lhibyte, llobyte;
// Get the position (in butes) of the end of the mpeg audio frame
int frameEnd = buffer_sstell(bs) / 8;
// find the maximum in the left and right channels
leftMax = rightMax = -1;
for (i = 0; i < TWOLAME_SAMPLES_PER_FRAME; i++) {
if (abs(leftpcm[i]) > leftMax)
leftMax = abs(leftpcm[i]);
if (abs(rightpcm[i]) > rightMax)
rightMax = abs(rightpcm[i]);
}
// fix any overflows
if (leftMax > 32767)
leftMax = 32767;
if (rightMax > 32767)
rightMax = 32767;
// convert max value to hi/lo bytes and write into buffer
lhibyte = leftMax / 256;
llobyte = leftMax - 256 * lhibyte;
// Write the left channel into the last two bytes of the frame
bs->buf[frameEnd - 1] = llobyte;
bs->buf[frameEnd - 2] = lhibyte;
bs->buf[frameEnd - 3] = 0;
// Only write the right channel energy info
// if we're in stereo mode.
if (glopts->mode != TWOLAME_MONO) {
rhibyte = rightMax / 256;
rlobyte = rightMax - 256 * rhibyte;
bs->buf[frameEnd - 4] = rlobyte;
bs->buf[frameEnd - 5] = rhibyte;
}
}
// vim:ts=4:sw=4:nowrap:
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