<?php
/////////////////////////////////////////////////////////////////
/// getID3() by James Heinrich <info@getid3.org> //
// available at http://getid3.sourceforge.net //
// or http://www.getid3.org //
/////////////////////////////////////////////////////////////////
// See readme.txt for more details //
/////////////////////////////////////////////////////////////////
// //
// module.audio.ac3.php //
// module for analyzing AC-3 (aka Dolby Digital) audio files //
// dependencies: NONE //
// ///
/////////////////////////////////////////////////////////////////
class getid3_ac3 extends getid3_handler
{
private $AC3header = '';
private $BSIoffset = 0;
public function Analyze() {
$info = &$this->getid3->info;
///AH
$info['ac3']['raw']['bsi'] = array();
$thisfile_ac3 = &$info['ac3'];
$thisfile_ac3_raw = &$thisfile_ac3['raw'];
$thisfile_ac3_raw_bsi = &$thisfile_ac3_raw['bsi'];
// http://www.atsc.org/standards/a_52a.pdf
$info['fileformat'] = 'ac3';
// An AC-3 serial coded audio bit stream is made up of a sequence of synchronization frames
// Each synchronization frame contains 6 coded audio blocks (AB), each of which represent 256
// new audio samples per channel. A synchronization information (SI) header at the beginning
// of each frame contains information needed to acquire and maintain synchronization. A
// bit stream information (BSI) header follows SI, and contains parameters describing the coded
// audio service. The coded audio blocks may be followed by an auxiliary data (Aux) field. At the
// end of each frame is an error check field that includes a CRC word for error detection. An
// additional CRC word is located in the SI header, the use of which, by a decoder, is optional.
//
// syncinfo() | bsi() | AB0 | AB1 | AB2 | AB3 | AB4 | AB5 | Aux | CRC
fseek($this->getid3->fp, $info['avdataoffset'], SEEK_SET);
$this->AC3header['syncinfo'] = fread($this->getid3->fp, 5);
$thisfile_ac3_raw['synchinfo']['synchword'] = substr($this->AC3header['syncinfo'], 0, 2);
$magic = "\x0B\x77";
if ($thisfile_ac3_raw['synchinfo']['synchword'] != $magic) {
$info['error'][] = 'Expecting "'.getid3_lib::PrintHexBytes($magic).'" at offset '.$info['avdataoffset'].', found "'.getid3_lib::PrintHexBytes($thisfile_ac3_raw['synchinfo']['synchword']).'"';
unset($info['fileformat'], $info['ac3']);
return false;
}
$info['audio']['dataformat'] = 'ac3';
$info['audio']['bitrate_mode'] = 'cbr';
$info['audio']['lossless'] = false;
// syncinfo() {
// syncword 16
// crc1 16
// fscod 2
// frmsizecod 6
// } /* end of syncinfo */
$thisfile_ac3_raw['synchinfo']['crc1'] = getid3_lib::LittleEndian2Int(substr($this->AC3header['syncinfo'], 2, 2));
$ac3_synchinfo_fscod_frmsizecod = getid3_lib::LittleEndian2Int(substr($this->AC3header['syncinfo'], 4, 1));
$thisfile_ac3_raw['synchinfo']['fscod'] = ($ac3_synchinfo_fscod_frmsizecod & 0xC0) >> 6;
$thisfile_ac3_raw['synchinfo']['frmsizecod'] = ($ac3_synchinfo_fscod_frmsizecod & 0x3F);
$thisfile_ac3['sample_rate'] = $this->AC3sampleRateCodeLookup($thisfile_ac3_raw['synchinfo']['fscod']);
if ($thisfile_ac3_raw['synchinfo']['fscod'] <= 3) {
$info['audio']['sample_rate'] = $thisfile_ac3['sample_rate'];
}
$thisfile_ac3['frame_length'] = $this->AC3frameSizeLookup($thisfile_ac3_raw['synchinfo']['frmsizecod'], $thisfile_ac3_raw['synchinfo']['fscod']);
$thisfile_ac3['bitrate'] = $this->AC3bitrateLookup($thisfile_ac3_raw['synchinfo']['frmsizecod']);
$info['audio']['bitrate'] = $thisfile_ac3['bitrate'];
$this->AC3header['bsi'] = getid3_lib::BigEndian2Bin(fread($this->getid3->fp, 15));
$ac3_bsi_offset = 0;
$thisfile_ac3_raw_bsi['bsid'] = $this->readHeaderBSI(5);
if ($thisfile_ac3_raw_bsi['bsid'] > 8) {
// Decoders which can decode version 8 will thus be able to decode version numbers less than 8.
// If this standard is extended by the addition of additional elements or features, a value of bsid greater than 8 will be used.
// Decoders built to this version of the standard will not be able to decode versions with bsid greater than 8.
$info['error'][] = 'Bit stream identification is version '.$thisfile_ac3_raw_bsi['bsid'].', but getID3() only understands up to version 8';
unset($thisfile_ac3);
return false;
}
$thisfile_ac3_raw_bsi['bsmod'] = $this->readHeaderBSI(3);
$thisfile_ac3_raw_bsi['acmod'] = $this->readHeaderBSI(3);
$thisfile_ac3['service_type'] = $this->AC3serviceTypeLookup($thisfile_ac3_raw_bsi['bsmod'], $thisfile_ac3_raw_bsi['acmod']);
$ac3_coding_mode = $this->AC3audioCodingModeLookup($thisfile_ac3_raw_bsi['acmod']);
foreach($ac3_coding_mode as $key => $value) {
$thisfile_ac3[$key] = $value;
}
switch ($thisfile_ac3_raw_bsi['acmod']) {
case 0:
case 1:
$info['audio']['channelmode'] = 'mono';
break;
case 3:
case 4:
$info['audio']['channelmode'] = 'stereo';
break;
default:
$info['audio']['channelmode'] = 'surround';
break;
}
$info['audio']['channels'] = $thisfile_ac3['num_channels'];
if ($thisfile_ac3_raw_bsi['acmod'] & 0x01) {
// If the lsb of acmod is a 1, center channel is in use and cmixlev follows in the bit stream.
$thisfile_ac3_raw_bsi['cmixlev'] = $this->readHeaderBSI(2);
$thisfile_ac3['center_mix_level'] = $this->AC3centerMixLevelLookup($thisfile_ac3_raw_bsi['cmixlev']);
}
if ($thisfile_ac3_raw_bsi['acmod'] & 0x04) {
// If the msb of acmod is a 1, surround channels are in use and surmixlev follows in the bit stream.
$thisfile_ac3_raw_bsi['surmixlev'] = $this->readHeaderBSI(2);
$thisfile_ac3['surround_mix_level'] = $this->AC3surroundMixLevelLookup($thisfile_ac3_raw_bsi['surmixlev']);
}
if ($thisfile_ac3_raw_bsi['acmod'] == 0x02) {
// When operating in the two channel mode, this 2-bit code indicates whether or not the program has been encoded in Dolby Surround.
$thisfile_ac3_raw_bsi['dsurmod'] = $this->readHeaderBSI(2);
$thisfile_ac3['dolby_surround_mode'] = $this->AC3dolbySurroundModeLookup($thisfile_ac3_raw_bsi['dsurmod']);
}
$thisfile_ac3_raw_bsi['lfeon'] = (bool) $this->readHeaderBSI(1);
$thisfile_ac3['lfe_enabled'] = $thisfile_ac3_raw_bsi['lfeon'];
if ($thisfile_ac3_raw_bsi['lfeon']) {
//$info['audio']['channels']++;
$info['audio']['channels'] .= '.1';
}
$thisfile_ac3['channels_enabled'] = $this->AC3channelsEnabledLookup($thisfile_ac3_raw_bsi['acmod'], $thisfile_ac3_raw_bsi['lfeon']);
// This indicates how far the average dialogue level is below digital 100 percent. Valid values are 1–31.
// 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.
$thisfile_ac3_raw_bsi['dialnorm'] = $this->readHeaderBSI(5);
$thisfile_ac3['dialogue_normalization'] = '-'.$thisfile_ac3_raw_bsi['dialnorm'].'dB';
$thisfile_ac3_raw_bsi['compre_flag'] = (bool) $this->readHeaderBSI(1);
if ($thisfile_ac3_raw_bsi['compre_flag']) {
$thisfile_ac3_raw_bsi['compr'] = $this->readHeaderBSI(8);
$thisfile_ac3['heavy_compression'] = $this->AC3heavyCompression($thisfile_ac3_raw_bsi['compr']);
}
$thisfile_ac3_raw_bsi['langcode_flag'] = (bool) $this->readHeaderBSI(1);
if ($thisfile_ac3_raw_bsi['langcode_flag']) {
$thisfile_ac3_raw_bsi['langcod'] = $this->readHeaderBSI(8);
}
$thisfile_ac3_raw_bsi['audprodie'] = (bool) $this->readHeaderBSI(1);
if ($thisfile_ac3_raw_bsi['audprodie']) {
$thisfile_ac3_raw_bsi['mixlevel'] = $this->readHeaderBSI(5);
$thisfile_ac3_raw_bsi['roomtyp'] = $this->readHeaderBSI(2);
$thisfile_ac3['mixing_level'] = (80 + $thisfile_ac3_raw_bsi['mixlevel']).'dB';
$thisfile_ac3['room_type'] = $this->AC3roomTypeLookup($thisfile_ac3_raw_bsi['roomtyp']);
}
if ($thisfile_ac3_raw_bsi['acmod'] == 0x00) {
// If acmod is 0, then two completely independent program channels (dual mono)
// are encoded into the bit stream, and are referenced as Ch1, Ch2. In this case,
// a number of additional items are present in BSI or audblk to fully describe Ch2.
// This indicates how far the average dialogue level is below digital 100 percent. Valid values are 1–31.
// 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.
$thisfile_ac3_raw_bsi['dialnorm2'] = $this->readHeaderBSI(5);
$thisfile_ac3['dialogue_normalization2'] = '-'.$thisfile_ac3_raw_bsi['dialnorm2'].'dB';
$thisfile_ac3_raw_bsi['compre_flag2'] = (bool) $this->readHeaderBSI(1);
if ($thisfile_ac3_raw_bsi['compre_flag2']) {
$thisfile_ac3_raw_bsi['compr2'] = $this->readHeaderBSI(8);
$thisfile_ac3['heavy_compression2'] = $this->AC3heavyCompression($thisfile_ac3_raw_bsi['compr2']);
}
$thisfile_ac3_raw_bsi['langcode_flag2'] = (bool) $this->readHeaderBSI(1);
if ($thisfile_ac3_raw_bsi['langcode_flag2']) {
$thisfile_ac3_raw_bsi['langcod2'] = $this->readHeaderBSI(8);
}
$thisfile_ac3_raw_bsi['audprodie2'] = (bool) $this->readHeaderBSI(1);
if ($thisfile_ac3_raw_bsi['audprodie2']) {
$thisfile_ac3_raw_bsi['mixlevel2'] = $this->readHeaderBSI(5);
$thisfile_ac3_raw_bsi['roomtyp2'] = $this->readHeaderBSI(2);
$thisfile_ac3['mixing_level2'] = (80 + $thisfile_ac3_raw_bsi['mixlevel2']).'dB';
$thisfile_ac3['room_type2'] = $this->AC3roomTypeLookup($thisfile_ac3_raw_bsi['roomtyp2']);
}
}
$thisfile_ac3_raw_bsi['copyright'] = (bool) $this->readHeaderBSI(1);
$thisfile_ac3_raw_bsi['original'] = (bool) $this->readHeaderBSI(1);
$thisfile_ac3_raw_bsi['timecode1_flag'] = (bool) $this->readHeaderBSI(1);
if ($thisfile_ac3_raw_bsi['timecode1_flag']) {
$thisfile_ac3_raw_bsi['timecode1'] = $this->readHeaderBSI(14);
}
$thisfile_ac3_raw_bsi['timecode2_flag'] = (bool) $this->readHeaderBSI(1);
if ($thisfile_ac3_raw_bsi['timecode2_flag']) {
$thisfile_ac3_raw_bsi['timecode2'] = $this->readHeaderBSI(14);
}
$thisfile_ac3_raw_bsi['addbsi_flag'] = (bool) $this->readHeaderBSI(1);
if ($thisfile_ac3_raw_bsi['addbsi_flag']) {
$thisfile_ac3_raw_bsi['addbsi_length'] = $this->readHeaderBSI(6);
$this->AC3header['bsi'] .= getid3_lib::BigEndian2Bin(fread($this->getid3->fp, $thisfile_ac3_raw_bsi['addbsi_length']));
$thisfile_ac3_raw_bsi['addbsi_data'] = substr($this->AC3header['bsi'], $this->BSIoffset, $thisfile_ac3_raw_bsi['addbsi_length'] * 8);
$this->BSIoffset += $thisfile_ac3_raw_bsi['addbsi_length'] * 8;
}
return true;
}
private function readHeaderBSI($length) {
$data = substr($this->AC3header['bsi'], $this->BSIoffset, $length);
$this->BSIoffset += $length;
return bindec($data);
}
public static function AC3sampleRateCodeLookup($fscod) {
static $AC3sampleRateCodeLookup = array(
0 => 48000,
1 => 44100,
2 => 32000,
3 => 'reserved' // If the reserved code is indicated, the decoder should not attempt to decode audio and should mute.
);
return (isset($AC3sampleRateCodeLookup[$fscod]) ? $AC3sampleRateCodeLookup[$fscod] : false);
}
public static function AC3serviceTypeLookup($bsmod, $acmod) {
static $AC3serviceTypeLookup = array();
if (empty($AC3serviceTypeLookup)) {
for ($i = 0; $i <= 7; $i++) {
$AC3serviceTypeLookup[0][$i] = 'main audio service: complete main (CM)';
$AC3serviceTypeLookup[1][$i] = 'main audio service: music and effects (ME)';
$AC3serviceTypeLookup[2][$i] = 'associated service: visually impaired (VI)';
$AC3serviceTypeLookup[3][$i] = 'associated service: hearing impaired (HI)';
$AC3serviceTypeLookup[4][$i] = 'associated service: dialogue (D)';
$AC3serviceTypeLookup[5][$i] = 'associated service: commentary (C)';
$AC3serviceTypeLookup[6][$i] = 'associated service: emergency (E)';
}
$AC3serviceTypeLookup[7][1] = 'associated service: voice over (VO)';
for ($i = 2; $i <= 7; $i++) {
$AC3serviceTypeLookup[7][$i] = 'main audio service: karaoke';
}
}
return (isset($AC3serviceTypeLookup[$bsmod][$acmod]) ? $AC3serviceTypeLookup[$bsmod][$acmod] : false);
}
public static function AC3audioCodingModeLookup($acmod) {
static $AC3audioCodingModeLookup = array();
if (empty($AC3audioCodingModeLookup)) {
// array(channel configuration, # channels (not incl LFE), channel order)
$AC3audioCodingModeLookup = array (
0 => array('channel_config'=>'1+1', 'num_channels'=>2, 'channel_order'=>'Ch1,Ch2'),
1 => array('channel_config'=>'1/0', 'num_channels'=>1, 'channel_order'=>'C'),
2 => array('channel_config'=>'2/0', 'num_channels'=>2, 'channel_order'=>'L,R'),
3 => array('channel_config'=>'3/0', 'num_channels'=>3, 'channel_order'=>'L,C,R'),
4 => array('channel_config'=>'2/1', 'num_channels'=>3, 'channel_order'=>'L,R,S'),
5 => array('channel_config'=>'3/1', 'num_channels'=>4, 'channel_order'=>'L,C,R,S'),
6 => array('channel_config'=>'2/2', 'num_channels'=>4, 'channel_order'=>'L,R,SL,SR'),
7 => array('channel_config'=>'3/2', 'num_channels'=>5, 'channel_order'=>'L,C,R,SL,SR')
);
}
return (isset($AC3audioCodingModeLookup[$acmod]) ? $AC3audioCodingModeLookup[$acmod] : false);
}
public static function AC3centerMixLevelLookup($cmixlev) {
static $AC3centerMixLevelLookup;
if (empty($AC3centerMixLevelLookup)) {
$AC3centerMixLevelLookup = array(
0 => pow(2, -3.0 / 6), // 0.707 (–3.0 dB)
1 => pow(2, -4.5 / 6), // 0.595 (–4.5 dB)
2 => pow(2, -6.0 / 6), // 0.500 (–6.0 dB)
3 => 'reserved'
);
}
return (isset($AC3centerMixLevelLookup[$cmixlev]) ? $AC3centerMixLevelLookup[$cmixlev] : false);
}
public static function AC3surroundMixLevelLookup($surmixlev) {
static $AC3surroundMixLevelLookup;
if (empty($AC3surroundMixLevelLookup)) {
$AC3surroundMixLevelLookup = array(
0 => pow(2, -3.0 / 6),
1 => pow(2, -6.0 / 6),
2 => 0,
3 => 'reserved'
);
}
return (isset($AC3surroundMixLevelLookup[$surmixlev]) ? $AC3surroundMixLevelLookup[$surmixlev] : false);
}
public static function AC3dolbySurroundModeLookup($dsurmod) {
static $AC3dolbySurroundModeLookup = array(
0 => 'not indicated',
1 => 'Not Dolby Surround encoded',
2 => 'Dolby Surround encoded',
3 => 'reserved'
);
return (isset($AC3dolbySurroundModeLookup[$dsurmod]) ? $AC3dolbySurroundModeLookup[$dsurmod] : false);
}
public static function AC3channelsEnabledLookup($acmod, $lfeon) {
$AC3channelsEnabledLookup = array(
'ch1'=>(bool) ($acmod == 0),
'ch2'=>(bool) ($acmod == 0),
'left'=>(bool) ($acmod > 1),
'right'=>(bool) ($acmod > 1),
'center'=>(bool) ($acmod & 0x01),
'surround_mono'=>false,
'surround_left'=>false,
'surround_right'=>false,
'lfe'=>$lfeon);
switch ($acmod) {
case 4:
case 5:
$AC3channelsEnabledLookup['surround_mono'] = true;
break;
case 6:
case 7:
$AC3channelsEnabledLookup['surround_left'] = true;
$AC3channelsEnabledLookup['surround_right'] = true;
break;
}
return $AC3channelsEnabledLookup;
}
public static function AC3heavyCompression($compre) {
// The first four bits indicate gain changes in 6.02dB increments which can be
// implemented with an arithmetic shift operation. The following four bits
// indicate linear gain changes, and require a 5-bit multiply.
// We will represent the two 4-bit fields of compr as follows:
// X0 X1 X2 X3 . Y4 Y5 Y6 Y7
// The meaning of the X values is most simply described by considering X to represent a 4-bit
// signed integer with values from –8 to +7. The gain indicated by X is then (X + 1) * 6.02 dB. The
// following table shows this in detail.
// Meaning of 4 msb of compr
// 7 +48.16 dB
// 6 +42.14 dB
// 5 +36.12 dB
// 4 +30.10 dB
// 3 +24.08 dB
// 2 +18.06 dB
// 1 +12.04 dB
// 0 +6.02 dB
// -1 0 dB
// -2 –6.02 dB
// -3 –12.04 dB
// -4 –18.06 dB
// -5 –24.08 dB
// -6 –30.10 dB
// -7 –36.12 dB
// -8 –42.14 dB
$fourbit = str_pad(decbin(($compre & 0xF0) >> 4), 4, '0', STR_PAD_LEFT);
if ($fourbit{0} == '1') {
$log_gain = -8 + bindec(substr($fourbit, 1));
} else {
$log_gain = bindec(substr($fourbit, 1));
}
$log_gain = ($log_gain + 1) * getid3_lib::RGADamplitude2dB(2);
// The value of Y is a linear representation of a gain change of up to –6 dB. Y is considered to
// be an unsigned fractional integer, with a leading value of 1, or: 0.1 Y4 Y5 Y6 Y7 (base 2). Y can
// represent values between 0.111112 (or 31/32) and 0.100002 (or 1/2). Thus, Y can represent gain
// changes from –0.28 dB to –6.02 dB.
$lin_gain = (16 + ($compre & 0x0F)) / 32;
// The combination of X and Y values allows compr to indicate gain changes from
// 48.16 – 0.28 = +47.89 dB, to
// –42.14 – 6.02 = –48.16 dB.
return $log_gain - $lin_gain;
}
public static function AC3roomTypeLookup($roomtyp) {
static $AC3roomTypeLookup = array(
0 => 'not indicated',
1 => 'large room, X curve monitor',
2 => 'small room, flat monitor',
3 => 'reserved'
);
return (isset($AC3roomTypeLookup[$roomtyp]) ? $AC3roomTypeLookup[$roomtyp] : false);
}
public static function AC3frameSizeLookup($frmsizecod, $fscod) {
$padding = (bool) ($frmsizecod % 2);
$framesizeid = floor($frmsizecod / 2);
static $AC3frameSizeLookup = array();
if (empty($AC3frameSizeLookup)) {
$AC3frameSizeLookup = array (
0 => array(128, 138, 192),
1 => array(40, 160, 174, 240),
2 => array(48, 192, 208, 288),
3 => array(56, 224, 242, 336),
4 => array(64, 256, 278, 384),
5 => array(80, 320, 348, 480),
6 => array(96, 384, 416, 576),
7 => array(112, 448, 486, 672),
8 => array(128, 512, 556, 768),
9 => array(160, 640, 696, 960),
10 => array(192, 768, 834, 1152),
11 => array(224, 896, 974, 1344),
12 => array(256, 1024, 1114, 1536),
13 => array(320, 1280, 1392, 1920),
14 => array(384, 1536, 1670, 2304),
15 => array(448, 1792, 1950, 2688),
16 => array(512, 2048, 2228, 3072),
17 => array(576, 2304, 2506, 3456),
18 => array(640, 2560, 2786, 3840)
);
}
if (($fscod == 1) && $padding) {
// frame lengths are padded by 1 word (16 bits) at 44100
$AC3frameSizeLookup[$frmsizecod] += 2;
}
return (isset($AC3frameSizeLookup[$framesizeid][$fscod]) ? $AC3frameSizeLookup[$framesizeid][$fscod] : false);
}
public static function AC3bitrateLookup($frmsizecod) {
$framesizeid = floor($frmsizecod / 2);
static $AC3bitrateLookup = array(
0 => 32000,
1 => 40000,
2 => 48000,
3 => 56000,
4 => 64000,
5 => 80000,
6 => 96000,
7 => 112000,
8 => 128000,
9 => 160000,
10 => 192000,
11 => 224000,
12 => 256000,
13 => 320000,
14 => 384000,
15 => 448000,
16 => 512000,
17 => 576000,
18 => 640000
);
return (isset($AC3bitrateLookup[$framesizeid]) ? $AC3bitrateLookup[$framesizeid] : false);
}
}
?>
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