mirror of
https://github.com/cookiengineer/audacity
synced 2025-05-04 17:49:45 +02:00
127 lines
3.3 KiB
C
127 lines
3.3 KiB
C
/*
|
|
* 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: energy.c,v 1.3 2008-02-01 19:44:32 richardash1981 Exp $
|
|
*
|
|
*/
|
|
|
|
|
|
#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:
|
|
|