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// +----------------------------------------------------------------------+
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// +----------------------------------------------------------------------+
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// | Copyright (c) 2002-2006 James Heinrich, Allan Hansen |
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// +----------------------------------------------------------------------+
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// | This source file is subject to version 2 of the GPL license, |
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// | that is bundled with this package in the file license.txt and is |
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// | available through the world-wide-web at the following url: |
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// | http://www.gnu.org/copyleft/gpl.html |
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// +----------------------------------------------------------------------+
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// | getID3() - http://getid3.sourceforge.net or http://www.getid3.org |
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// +----------------------------------------------------------------------+
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// | Authors: James Heinrich <info�getid3*org> |
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// | Allan Hansen <ah�artemis*dk> |
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// +----------------------------------------------------------------------+
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// | module.audio.ac3.php |
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// | Module for analyzing AC-3 (aka Dolby Digital) audio files |
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// | dependencies: NONE |
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// +----------------------------------------------------------------------+
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// $Id: module.audio.ac3.php,v 1.3 2006/11/02 10:48:01 ah Exp $
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class getid3_ac3 extends getid3_handler
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public function Analyze() {
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$getid3 = $this->getid3;
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// http://www.atsc.org/standards/a_52a.pdf
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$getid3->info['fileformat'] = 'ac3';
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$getid3->info['audio']['dataformat'] = 'ac3';
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$getid3->info['audio']['bitrate_mode'] = 'cbr';
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$getid3->info['audio']['lossless'] = false;
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$getid3->info['ac3']['raw']['bsi'] = array ();
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$info_ac3 = &$getid3->info['ac3'];
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$info_ac3_raw = &$info_ac3['raw'];
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$info_ac3_raw_bsi = &$info_ac3_raw['bsi'];
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// An AC-3 serial coded audio bit stream is made up of a sequence of synchronization frames
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// Each synchronization frame contains 6 coded audio blocks (AB), each of which represent 256
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// new audio samples per channel. A synchronization information (SI) header at the beginning
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// of each frame contains information needed to acquire and maintain synchronization. A
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// bit stream information (BSI) header follows SI, and contains parameters describing the coded
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// audio service. The coded audio blocks may be followed by an auxiliary data (Aux) field. At the
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// end of each frame is an error check field that includes a CRC word for error detection. An
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// additional CRC word is located in the SI header, the use of which, by a decoder, is optional.
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// syncinfo() | bsi() | AB0 | AB1 | AB2 | AB3 | AB4 | AB5 | Aux | CRC
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$this->fseek($getid3->info['avdataoffset'], SEEK_SET);
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$ac3_header['syncinfo'] = $this->fread(5);
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$info_ac3_raw['synchinfo']['synchword'] = substr($ac3_header['syncinfo'], 0, 2);
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if ($info_ac3_raw['synchinfo']['synchword'] != "\x0B\x77") {
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throw new getid3_exception('Expecting "\x0B\x77" at offset '.$getid3->info['avdataoffset'].', found \x'.strtoupper(dechex($ac3_header['syncinfo']{0})).'\x'.strtoupper(dechex($ac3_header['syncinfo']{1})).' instead');
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// } /* end of syncinfo */
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$info_ac3_raw['synchinfo']['crc1'] = getid3_lib::LittleEndian2Int(substr($ac3_header['syncinfo'], 2, 2));
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$ac3_synchinfo_fscod_frmsizecod = getid3_lib::LittleEndian2Int(substr($ac3_header['syncinfo'], 4, 1));
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$info_ac3_raw['synchinfo']['fscod'] = ($ac3_synchinfo_fscod_frmsizecod & 0xC0) >> 6;
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$info_ac3_raw['synchinfo']['frmsizecod'] = ($ac3_synchinfo_fscod_frmsizecod & 0x3F);
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$info_ac3['sample_rate'] = getid3_ac3::AC3sampleRateCodeLookup($info_ac3_raw['synchinfo']['fscod']);
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if ($info_ac3_raw['synchinfo']['fscod'] <= 3) {
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$getid3->info['audio']['sample_rate'] = $info_ac3['sample_rate'];
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$info_ac3['frame_length'] = getid3_ac3::AC3frameSizeLookup($info_ac3_raw['synchinfo']['frmsizecod'], $info_ac3_raw['synchinfo']['fscod']);
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$info_ac3['bitrate'] = getid3_ac3::AC3bitrateLookup($info_ac3_raw['synchinfo']['frmsizecod']);
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$getid3->info['audio']['bitrate'] = $info_ac3['bitrate'];
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$ac3_header['bsi'] = getid3_lib::BigEndian2Bin($this->fread(15));
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$info_ac3_raw_bsi['bsid'] = bindec(substr($ac3_header['bsi'], 0, 5));
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if ($info_ac3_raw_bsi['bsid'] > 8) {
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// Decoders which can decode version 8 will thus be able to decode version numbers less than 8.
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// If this standard is extended by the addition of additional elements or features, a value of bsid greater than 8 will be used.
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// Decoders built to this version of the standard will not be able to decode versions with bsid greater than 8.
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throw new getid3_exception('Bit stream identification is version '.$info_ac3_raw_bsi['bsid'].', but getID3() only understands up to version 8');
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$info_ac3_raw_bsi['bsmod'] = bindec(substr($ac3_header['bsi'], 5, 3));
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$info_ac3_raw_bsi['acmod'] = bindec(substr($ac3_header['bsi'], 8, 3));
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$info_ac3['service_type'] = getid3_ac3::AC3serviceTypeLookup($info_ac3_raw_bsi['bsmod'], $info_ac3_raw_bsi['acmod']);
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$ac3_coding_mode = getid3_ac3::AC3audioCodingModeLookup($info_ac3_raw_bsi['acmod']);
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foreach($ac3_coding_mode as $key => $value) {
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$info_ac3[$key] = $value;
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switch ($info_ac3_raw_bsi['acmod']) {
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$getid3->info['audio']['channelmode'] = 'mono';
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$getid3->info['audio']['channelmode'] = 'stereo';
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$getid3->info['audio']['channelmode'] = 'surround';
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$getid3->info['audio']['channels'] = $info_ac3['num_channels'];
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if ($info_ac3_raw_bsi['acmod'] & 0x01) {
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// If the lsb of acmod is a 1, center channel is in use and cmixlev follows in the bit stream.
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$info_ac3_raw_bsi['cmixlev'] = bindec(substr($ac3_header['bsi'], $offset, 2));
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$info_ac3['center_mix_level'] = getid3_ac3::AC3centerMixLevelLookup($info_ac3_raw_bsi['cmixlev']);
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if ($info_ac3_raw_bsi['acmod'] & 0x04) {
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// If the msb of acmod is a 1, surround channels are in use and surmixlev follows in the bit stream.
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$info_ac3_raw_bsi['surmixlev'] = bindec(substr($ac3_header['bsi'], $offset, 2));
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$info_ac3['surround_mix_level'] = getid3_ac3::AC3surroundMixLevelLookup($info_ac3_raw_bsi['surmixlev']);
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if ($info_ac3_raw_bsi['acmod'] == 0x02) {
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// When operating in the two channel mode, this 2-bit code indicates whether or not the program has been encoded in Dolby Surround.
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$info_ac3_raw_bsi['dsurmod'] = bindec(substr($ac3_header['bsi'], $offset, 2));
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$info_ac3['dolby_surround_mode'] = getid3_ac3::AC3dolbySurroundModeLookup($info_ac3_raw_bsi['dsurmod']);
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$info_ac3_raw_bsi['lfeon'] = $ac3_header['bsi']{$offset++} == '1';
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$info_ac3['lfe_enabled'] = $info_ac3_raw_bsi['lfeon'];
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if ($info_ac3_raw_bsi['lfeon']) {
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$getid3->info['audio']['channels'] .= '.1';
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$info_ac3['channels_enabled'] = getid3_ac3::AC3channelsEnabledLookup($info_ac3_raw_bsi['acmod'], $info_ac3_raw_bsi['lfeon']);
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// This indicates how far the average dialogue level is below digital 100 percent. Valid values are 1�31.
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// The value of 0 is reserved. The values of 1 to 31 are interpreted as -1 dB to -31 dB with respect to digital 100 percent.
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$info_ac3_raw_bsi['dialnorm'] = bindec(substr($ac3_header['bsi'], $offset, 5));
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$info_ac3['dialogue_normalization'] = '-'.$info_ac3_raw_bsi['dialnorm'].'dB';
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$info_ac3_raw_bsi['compre_flag'] = $ac3_header['bsi']{$offset++} == '1';
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if ($info_ac3_raw_bsi['compre_flag']) {
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$info_ac3_raw_bsi['compr'] = bindec(substr($ac3_header['bsi'], $offset, 8));
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$info_ac3['heavy_compression'] = getid3_ac3::AC3heavyCompression($info_ac3_raw_bsi['compr']);
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$info_ac3_raw_bsi['langcode_flag'] = $ac3_header['bsi']{$offset++} == '1';
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if ($info_ac3_raw_bsi['langcode_flag']) {
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$info_ac3_raw_bsi['langcod'] = bindec(substr($ac3_header['bsi'], $offset, 8));
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$info_ac3_raw_bsi['audprodie'] = $ac3_header['bsi']{$offset++} == '1';
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if ($info_ac3_raw_bsi['audprodie']) {
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$info_ac3_raw_bsi['mixlevel'] = bindec(substr($ac3_header['bsi'], $offset, 5));
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$info_ac3_raw_bsi['roomtyp'] = bindec(substr($ac3_header['bsi'], $offset, 2));
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$info_ac3['mixing_level'] = (80 + $info_ac3_raw_bsi['mixlevel']).'dB';
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$info_ac3['room_type'] = getid3_ac3::AC3roomTypeLookup($info_ac3_raw_bsi['roomtyp']);
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if ($info_ac3_raw_bsi['acmod'] == 0x00) {
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// If acmod is 0, then two completely independent program channels (dual mono)
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// are encoded into the bit stream, and are referenced as Ch1, Ch2. In this case,
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// a number of additional items are present in BSI or audblk to fully describe Ch2.
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// This indicates how far the average dialogue level is below digital 100 percent. Valid values are 1�31.
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// The value of 0 is reserved. The values of 1 to 31 are interpreted as -1 dB to -31 dB with respect to digital 100 percent.
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$info_ac3_raw_bsi['dialnorm2'] = bindec(substr($ac3_header['bsi'], $offset, 5));
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$info_ac3['dialogue_normalization2'] = '-'.$info_ac3_raw_bsi['dialnorm2'].'dB';
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$info_ac3_raw_bsi['compre_flag2'] = $ac3_header['bsi']{$offset++} == '1';
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if ($info_ac3_raw_bsi['compre_flag2']) {
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$info_ac3_raw_bsi['compr2'] = bindec(substr($ac3_header['bsi'], $offset, 8));
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$info_ac3['heavy_compression2'] = getid3_ac3::AC3heavyCompression($info_ac3_raw_bsi['compr2']);
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$info_ac3_raw_bsi['langcode_flag2'] = $ac3_header['bsi']{$offset++} == '1';
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if ($info_ac3_raw_bsi['langcode_flag2']) {
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$info_ac3_raw_bsi['langcod2'] = bindec(substr($ac3_header['bsi'], $offset, 8));
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$info_ac3_raw_bsi['audprodie2'] = $ac3_header['bsi']{$offset++} == '1';
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if ($info_ac3_raw_bsi['audprodie2']) {
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$info_ac3_raw_bsi['mixlevel2'] = bindec(substr($ac3_header['bsi'], $offset, 5));
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$info_ac3_raw_bsi['roomtyp2'] = bindec(substr($ac3_header['bsi'], $offset, 2));
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$info_ac3['mixing_level2'] = (80 + $info_ac3_raw_bsi['mixlevel2']).'dB';
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$info_ac3['room_type2'] = getid3_ac3::AC3roomTypeLookup($info_ac3_raw_bsi['roomtyp2']);
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$info_ac3_raw_bsi['copyright'] = $ac3_header['bsi']{$offset++} == '1';
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$info_ac3_raw_bsi['original'] = $ac3_header['bsi']{$offset++} == '1';
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$info_ac3_raw_bsi['timecode1_flag'] = $ac3_header['bsi']{$offset++} == '1';
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if ($info_ac3_raw_bsi['timecode1_flag']) {
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$info_ac3_raw_bsi['timecode1'] = bindec(substr($ac3_header['bsi'], $offset, 14));
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$info_ac3_raw_bsi['timecode2_flag'] = $ac3_header['bsi']{$offset++} == '1';
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if ($info_ac3_raw_bsi['timecode2_flag']) {
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$info_ac3_raw_bsi['timecode2'] = bindec(substr($ac3_header['bsi'], $offset, 14));
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$info_ac3_raw_bsi['addbsi_flag'] = $ac3_header['bsi']{$offset++} == '1';
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if ($info_ac3_raw_bsi['addbsi_flag']) {
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$info_ac3_raw_bsi['addbsi_length'] = bindec(substr($ac3_header['bsi'], $offset, 6));
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$ac3_header['bsi'] .= getid3_lib::BigEndian2Bin($this->fread($info_ac3_raw_bsi['addbsi_length']));
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$info_ac3_raw_bsi['addbsi_data'] = substr($ac3_header['bsi'], 119, $info_ac3_raw_bsi['addbsi_length'] * 8);
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public static function AC3sampleRateCodeLookup($fscod) {
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static $lookup = array (
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3 => 'reserved' // If the reserved code is indicated, the decoder should not attempt to decode audio and should mute.
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return (isset($lookup[$fscod]) ? $lookup[$fscod] : false);
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public static function AC3serviceTypeLookup($bsmod, $acmod) {
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static $lookup = array (
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0 => 'main audio service: complete main (CM)',
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1 => 'main audio service: music and effects (ME)',
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2 => 'associated service: visually impaired (VI)',
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3 => 'associated service: hearing impaired (HI)',
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4 => 'associated service: dialogue (D)',
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5 => 'associated service: commentary (C)',
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6 => 'associated service: emergency (E)',
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7 => 'main audio service: karaoke'
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if ($bsmod == 7 && $acmod == 1) {
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return 'associated service: voice over (VO)';
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return (isset($lookup[$bsmod]) ? $lookup[$bsmod] : false);
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public static function AC3audioCodingModeLookup($acmod) {
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// array (channel configuration, # channels (not incl LFE), channel order)
293
static $lookup = array (
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0 => array ('channel_config'=>'1+1', 'num_channels'=>2, 'channel_order'=>'Ch1,Ch2'),
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1 => array ('channel_config'=>'1/0', 'num_channels'=>1, 'channel_order'=>'C'),
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2 => array ('channel_config'=>'2/0', 'num_channels'=>2, 'channel_order'=>'L,R'),
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3 => array ('channel_config'=>'3/0', 'num_channels'=>3, 'channel_order'=>'L,C,R'),
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4 => array ('channel_config'=>'2/1', 'num_channels'=>3, 'channel_order'=>'L,R,S'),
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5 => array ('channel_config'=>'3/1', 'num_channels'=>4, 'channel_order'=>'L,C,R,S'),
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6 => array ('channel_config'=>'2/2', 'num_channels'=>4, 'channel_order'=>'L,R,SL,SR'),
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7 => array ('channel_config'=>'3/2', 'num_channels'=>5, 'channel_order'=>'L,C,R,SL,SR')
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return (isset($lookup[$acmod]) ? $lookup[$acmod] : false);
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public static function AC3centerMixLevelLookup($cmixlev) {
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0 => pow(2, -3.0 / 6), // 0.707 (�3.0 dB)
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1 => pow(2, -4.5 / 6), // 0.595 (�4.5 dB)
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2 => pow(2, -6.0 / 6), // 0.500 (�6.0 dB)
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return (isset($lookup[$cmixlev]) ? $lookup[$cmixlev] : false);
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public static function AC3surroundMixLevelLookup($surmixlev) {
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0 => pow(2, -3.0 / 6),
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1 => pow(2, -6.0 / 6),
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return (isset($lookup[$surmixlev]) ? $lookup[$surmixlev] : false);
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public static function AC3dolbySurroundModeLookup($dsurmod) {
342
static $lookup = array (
343
0 => 'not indicated',
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1 => 'Not Dolby Surround encoded',
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2 => 'Dolby Surround encoded',
348
return (isset($lookup[$dsurmod]) ? $lookup[$dsurmod] : false);
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public static function AC3channelsEnabledLookup($acmod, $lfeon) {
356
'ch1' => $acmod == 0,
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'ch2' => $acmod == 0,
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'left' => $acmod > 1,
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'right' => $acmod > 1,
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'center' => (bool)($acmod & 0x01),
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'surround_mono' => $acmod == 4 || $acmod == 5,
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'surround_left' => $acmod == 6 || $acmod == 7,
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'surround_right' => $acmod == 6 || $acmod == 7,
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public static function AC3heavyCompression($compre) {
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// The first four bits indicate gain changes in 6.02dB increments which can be
373
// implemented with an arithmetic shift operation. The following four bits
374
// indicate linear gain changes, and require a 5-bit multiply.
375
// We will represent the two 4-bit fields of compr as follows:
376
// X0 X1 X2 X3 . Y4 Y5 Y6 Y7
377
// The meaning of the X values is most simply described by considering X to represent a 4-bit
378
// signed integer with values from �8 to +7. The gain indicated by X is then (X + 1) * 6.02 dB. The
379
// following table shows this in detail.
381
// Meaning of 4 msb of compr
399
$fourbit = str_pad(decbin(($compre & 0xF0) >> 4), 4, '0', STR_PAD_LEFT);
400
if ($fourbit{0} == '1') {
401
$log_gain = -8 + bindec(substr($fourbit, 1));
403
$log_gain = bindec(substr($fourbit, 1));
405
$log_gain = ($log_gain + 1) * (20 * log10(2));
407
// The value of Y is a linear representation of a gain change of up to �6 dB. Y is considered to
408
// be an unsigned fractional integer, with a leading value of 1, or: 0.1 Y4 Y5 Y6 Y7 (base 2). Y can
409
// represent values between 0.111112 (or 31/32) and 0.100002 (or 1/2). Thus, Y can represent gain
410
// changes from �0.28 dB to �6.02 dB.
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$lin_gain = (16 + ($compre & 0x0F)) / 32;
414
// The combination of X and Y values allows compr to indicate gain changes from
415
// 48.16 � 0.28 = +47.89 dB, to
416
// �42.14 � 6.02 = �48.16 dB.
418
return $log_gain - $lin_gain;
423
public static function AC3roomTypeLookup($roomtyp) {
425
static $lookup = array (
426
0 => 'not indicated',
427
1 => 'large room, X curve monitor',
428
2 => 'small room, flat monitor',
431
return (isset($lookup[$roomtyp]) ? $lookup[$roomtyp] : false);
436
public static function AC3frameSizeLookup($frmsizecod, $fscod) {
438
$padding = (bool)($frmsizecod % 2);
439
$frame_size_id = floor($frmsizecod / 2);
441
static $lookup = array (
442
0 => array (128, 138, 192),
443
1 => array (40, 160, 174, 240),
444
2 => array (48, 192, 208, 288),
445
3 => array (56, 224, 242, 336),
446
4 => array (64, 256, 278, 384),
447
5 => array (80, 320, 348, 480),
448
6 => array (96, 384, 416, 576),
449
7 => array (112, 448, 486, 672),
450
8 => array (128, 512, 556, 768),
451
9 => array (160, 640, 696, 960),
452
10 => array (192, 768, 834, 1152),
453
11 => array (224, 896, 974, 1344),
454
12 => array (256, 1024, 1114, 1536),
455
13 => array (320, 1280, 1392, 1920),
456
14 => array (384, 1536, 1670, 2304),
457
15 => array (448, 1792, 1950, 2688),
458
16 => array (512, 2048, 2228, 3072),
459
17 => array (576, 2304, 2506, 3456),
460
18 => array (640, 2560, 2786, 3840)
462
if (($fscod == 1) && $padding) {
463
// frame lengths are padded by 1 word (16 bits) at 44100
464
$lookup[$frmsizecod] += 2;
466
return (isset($lookup[$frame_size_id][$fscod]) ? $lookup[$frame_size_id][$fscod] : false);
471
public static function AC3bitrateLookup($frmsizecod) {
473
static $lookup = array (
494
$frame_size_id = floor($frmsizecod / 2);
495
return (isset($lookup[$frame_size_id]) ? $lookup[$frame_size_id] : false);
b'\\ No newline at end of file'
added
removed
modules/getid3/module.audio.ac3.php
