mirror of
https://github.com/cookiengineer/audacity
synced 2025-11-04 08:04:06 +01:00
124 lines
3.5 KiB
C
124 lines
3.5 KiB
C
/*
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* TwoLAME: an optimized MPEG Audio Layer Two encoder
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*
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* Copyright (C) 2001-2004 Michael Cheng
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* Copyright (C) 2004-2006 The TwoLAME Project
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*
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* $Id$
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*
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include "twolame.h"
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#include "common.h"
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#include "bitbuffer.h"
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#include "energy.h"
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// Returns the desired number of ancillary bits to be
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// reserved at the end of the frame
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int get_required_energy_bits(twolame_options * glopts)
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{
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if (glopts->mode == TWOLAME_MONO) {
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// only 2 bytes + zero at n-3 needed for energy level for mono channel
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return 24;
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} else {
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// 5 bytes for the stereo energy info
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return 40;
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}
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}
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// Calculates the energy levels of current frame and
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// inserts it into the end of the frame
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void do_energy_levels(twolame_options * glopts, bit_stream * bs)
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{
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/* Reference: Using the BWF Energy Levels in AudioScience Bitstreams
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http://www.audioscience.com/internet/download/notes/note0001_MPEG_energy.pdf
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Specification of the Broadcast Wave Format: Supplement 1 - MPEG audio
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http://www.ebu.ch/CMSimages/en/tec_doc_t3285_s1_tcm6-10545.pdf
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http://www.sr.se/utveckling/tu/bwf/
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The absolute peak of the PCM file for the left and right channel in this frame are written
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into the last 5 bytes of the frame.
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The last 5 bytes *must* be reserved for this to work correctly (otherwise you'll be
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overwriting mpeg audio data) */
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short int *leftpcm = glopts->buffer[0];
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short int *rightpcm = glopts->buffer[1];
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int i, leftMax, rightMax;
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unsigned char rhibyte, rlobyte, lhibyte, llobyte;
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// Get the position (in butes) of the end of the mpeg audio frame
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int frameEnd = buffer_sstell(bs) / 8;
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// find the maximum in the left and right channels
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leftMax = rightMax = -1;
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for (i = 0; i < TWOLAME_SAMPLES_PER_FRAME; i++) {
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if (abs(leftpcm[i]) > leftMax)
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leftMax = abs(leftpcm[i]);
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if (abs(rightpcm[i]) > rightMax)
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rightMax = abs(rightpcm[i]);
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}
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// fix any overflows
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if (leftMax > 32767)
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leftMax = 32767;
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if (rightMax > 32767)
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rightMax = 32767;
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// convert max value to hi/lo bytes and write into buffer
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lhibyte = leftMax / 256;
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llobyte = leftMax - 256 * lhibyte;
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// Write the left channel into the last two bytes of the frame
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bs->buf[frameEnd - 1] = llobyte;
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bs->buf[frameEnd - 2] = lhibyte;
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bs->buf[frameEnd - 3] = 0;
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// Only write the right channel energy info
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// if we're in stereo mode.
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if (glopts->mode != TWOLAME_MONO) {
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rhibyte = rightMax / 256;
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rlobyte = rightMax - 256 * rhibyte;
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bs->buf[frameEnd - 4] = rlobyte;
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bs->buf[frameEnd - 5] = rhibyte;
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}
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}
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// vim:ts=4:sw=4:nowrap:
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