<?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 = array();

      private $BSIoffset = 0;

      const syncword = "\x0B\x77";

  
  	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

  		// syncinfo() {
  		// 	 syncword    16
  		// 	 crc1        16
  		// 	 fscod        2
  		// 	 frmsizecod   6
  		// } /* end of syncinfo */

  		$this->fseek($info['avdataoffset']);
  		$this->AC3header['syncinfo'] = $this->fread(5);
  
  		if (strpos($this->AC3header['syncinfo'], self::syncword) === 0) {
  			$thisfile_ac3_raw['synchinfo']['synchword'] = self::syncword;
  			$offset = 2;
  		} else {
  			if (!$this->isDependencyFor('matroska')) {
  				unset($info['fileformat'], $info['ac3']);
  				return $this->error('Expecting "'.getid3_lib::PrintHexBytes(self::syncword).'" at offset '.$info['avdataoffset'].', found "'.getid3_lib::PrintHexBytes(substr($this->AC3header['syncinfo'], 0, 2)).'"');
  			}
  			$offset = 0;
  			$this->fseek(-2, SEEK_CUR);
  		}
  
  		$info['audio']['dataformat']   = 'ac3';
  		$info['audio']['bitrate_mode'] = 'cbr';
  		$info['audio']['lossless']     = false;
  
  		$thisfile_ac3_raw['synchinfo']['crc1']       = getid3_lib::LittleEndian2Int(substr($this->AC3header['syncinfo'], $offset, 2));
  		$ac3_synchinfo_fscod_frmsizecod              = getid3_lib::LittleEndian2Int(substr($this->AC3header['syncinfo'], ($offset + 2), 1));

  		$thisfile_ac3_raw['synchinfo']['fscod']      = ($ac3_synchinfo_fscod_frmsizecod & 0xC0) >> 6;
  		$thisfile_ac3_raw['synchinfo']['frmsizecod'] = ($ac3_synchinfo_fscod_frmsizecod & 0x3F);

  		$thisfile_ac3['sample_rate'] = self::sampleRateCodeLookup($thisfile_ac3_raw['synchinfo']['fscod']);

  		if ($thisfile_ac3_raw['synchinfo']['fscod'] <= 3) {
  			$info['audio']['sample_rate'] = $thisfile_ac3['sample_rate'];
  		}

  		$thisfile_ac3['frame_length'] = self::frameSizeLookup($thisfile_ac3_raw['synchinfo']['frmsizecod'], $thisfile_ac3_raw['synchinfo']['fscod']);
  		$thisfile_ac3['bitrate']      = self::bitrateLookup($thisfile_ac3_raw['synchinfo']['frmsizecod']);

  		$info['audio']['bitrate'] = $thisfile_ac3['bitrate'];

  		$this->AC3header['bsi'] = getid3_lib::BigEndian2Bin($this->fread(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.

  			$this->error('Bit stream identification is version '.$thisfile_ac3_raw_bsi['bsid'].', but getID3() only understands up to version 8');
  		    unset($info['ac3']);

  			return false;
  		}
  
  		$thisfile_ac3_raw_bsi['bsmod'] = $this->readHeaderBSI(3);
  		$thisfile_ac3_raw_bsi['acmod'] = $this->readHeaderBSI(3);

  		$thisfile_ac3['service_type'] = self::serviceTypeLookup($thisfile_ac3_raw_bsi['bsmod'], $thisfile_ac3_raw_bsi['acmod']);
  		$ac3_coding_mode = self::audioCodingModeLookup($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);

  			$thisfile_ac3['center_mix_level'] = self::centerMixLevelLookup($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);

  			$thisfile_ac3['surround_mix_level'] = self::surroundMixLevelLookup($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);

  			$thisfile_ac3['dolby_surround_mode'] = self::dolbySurroundModeLookup($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';
  		}

  		$thisfile_ac3['channels_enabled'] = self::channelsEnabledLookup($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);

  			$thisfile_ac3['heavy_compression'] = self::heavyCompression($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';

  			$thisfile_ac3['room_type']    = self::roomTypeLookup($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);

  				$thisfile_ac3['heavy_compression2'] = self::heavyCompression($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';

  				$thisfile_ac3['room_type2']    = self::roomTypeLookup($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);

  			$this->AC3header['bsi'] .= getid3_lib::BigEndian2Bin($this->fread($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 sampleRateCodeLookup($fscod) {
  		static $sampleRateCodeLookup = 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($sampleRateCodeLookup[$fscod]) ? $sampleRateCodeLookup[$fscod] : false);

  	}

  	public static function serviceTypeLookup($bsmod, $acmod) {
  		static $serviceTypeLookup = array();
  		if (empty($serviceTypeLookup)) {

  			for ($i = 0; $i <= 7; $i++) {

  				$serviceTypeLookup[0][$i] = 'main audio service: complete main (CM)';
  				$serviceTypeLookup[1][$i] = 'main audio service: music and effects (ME)';
  				$serviceTypeLookup[2][$i] = 'associated service: visually impaired (VI)';
  				$serviceTypeLookup[3][$i] = 'associated service: hearing impaired (HI)';
  				$serviceTypeLookup[4][$i] = 'associated service: dialogue (D)';
  				$serviceTypeLookup[5][$i] = 'associated service: commentary (C)';
  				$serviceTypeLookup[6][$i] = 'associated service: emergency (E)';

  			}

  			$serviceTypeLookup[7][1]      = 'associated service: voice over (VO)';

  			for ($i = 2; $i <= 7; $i++) {

  				$serviceTypeLookup[7][$i] = 'main audio service: karaoke';

  			}
  		}

  		return (isset($serviceTypeLookup[$bsmod][$acmod]) ? $serviceTypeLookup[$bsmod][$acmod] : false);

  	}

  	public static function audioCodingModeLookup($acmod) {
  		// array(channel configuration, # channels (not incl LFE), channel order)
  		static $audioCodingModeLookup = array (
  			0 => array('channel_config'=>'1+1', 'num_channels'=>2, 'channel_order'=>'Ch1,Ch2'),
  			1 => array('channel_config'=>'1/0', 'num_channels'=>1, 'channel_order'=>'C'),
  			2 => array('channel_config'=>'2/0', 'num_channels'=>2, 'channel_order'=>'L,R'),
  			3 => array('channel_config'=>'3/0', 'num_channels'=>3, 'channel_order'=>'L,C,R'),
  			4 => array('channel_config'=>'2/1', 'num_channels'=>3, 'channel_order'=>'L,R,S'),
  			5 => array('channel_config'=>'3/1', 'num_channels'=>4, 'channel_order'=>'L,C,R,S'),
  			6 => array('channel_config'=>'2/2', 'num_channels'=>4, 'channel_order'=>'L,R,SL,SR'),
  			7 => array('channel_config'=>'3/2', 'num_channels'=>5, 'channel_order'=>'L,C,R,SL,SR'),
  		);
  		return (isset($audioCodingModeLookup[$acmod]) ? $audioCodingModeLookup[$acmod] : false);

  	}

  	public static function centerMixLevelLookup($cmixlev) {
  		static $centerMixLevelLookup;
  		if (empty($centerMixLevelLookup)) {
  			$centerMixLevelLookup = 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($centerMixLevelLookup[$cmixlev]) ? $centerMixLevelLookup[$cmixlev] : false);

  	}

  	public static function surroundMixLevelLookup($surmixlev) {
  		static $surroundMixLevelLookup;
  		if (empty($surroundMixLevelLookup)) {
  			$surroundMixLevelLookup = array(

  				0 => pow(2, -3.0 / 6),
  				1 => pow(2, -6.0 / 6),
  				2 => 0,
  				3 => 'reserved'
  			);
  		}

  		return (isset($surroundMixLevelLookup[$surmixlev]) ? $surroundMixLevelLookup[$surmixlev] : false);

  	}

  	public static function dolbySurroundModeLookup($dsurmod) {
  		static $dolbySurroundModeLookup = array(

  			0 => 'not indicated',
  			1 => 'Not Dolby Surround encoded',
  			2 => 'Dolby Surround encoded',
  			3 => 'reserved'
  		);

  		return (isset($dolbySurroundModeLookup[$dsurmod]) ? $dolbySurroundModeLookup[$dsurmod] : false);

  	}

  	public static function channelsEnabledLookup($acmod, $lfeon) {
  		$lookup = 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:

  				$lookup['surround_mono']  = true;

  				break;
  			case 6:
  			case 7:

  				$lookup['surround_left']  = true;
  				$lookup['surround_right'] = true;

  				break;
  		}

  		return $lookup;

  	}

  	public static function heavyCompression($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 roomTypeLookup($roomtyp) {
  		static $roomTypeLookup = array(

  			0 => 'not indicated',
  			1 => 'large room, X curve monitor',
  			2 => 'small room, flat monitor',
  			3 => 'reserved'
  		);

  		return (isset($roomTypeLookup[$roomtyp]) ? $roomTypeLookup[$roomtyp] : false);

  	}

  	public static function frameSizeLookup($frmsizecod, $fscod) {

  		$padding     = (bool) ($frmsizecod % 2);
  		$framesizeid =   floor($frmsizecod / 2);

  		static $frameSizeLookup = array();
  		if (empty($frameSizeLookup)) {
  			$frameSizeLookup = 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

  			$frameSizeLookup[$frmsizecod] += 2;

  		}

  		return (isset($frameSizeLookup[$framesizeid][$fscod]) ? $frameSizeLookup[$framesizeid][$fscod] : false);

  	}

  	public static function bitrateLookup($frmsizecod) {

  		$framesizeid =   floor($frmsizecod / 2);

  		static $bitrateLookup = 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($bitrateLookup[$framesizeid]) ? $bitrateLookup[$framesizeid] : false);

  	}
  
  
  }