Timers WIP

Added getID3

1 files changed, 497 insertions, 0 deletions

diff --git a/getid3/module.audio.ac3.php b/getid3/module.audio.ac3.php
new file mode 100644
index 0000000..9809a47
--- /dev/null
+++ b/getid3/module.audio.ac3.php
@@ -0,0 +1,497 @@
+<?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
+{
+
+	function getid3_ac3(&$fd, &$ThisFileInfo) {
+
+		///AH
+		$ThisFileInfo['ac3']['raw']['bsi'] = array();
+		$thisfile_ac3                      = &$ThisFileInfo['ac3'];
+		$thisfile_ac3_raw                  = &$thisfile_ac3['raw'];
+		$thisfile_ac3_raw_bsi              = &$thisfile_ac3_raw['bsi'];
+
+
+		// http://www.atsc.org/standards/a_52a.pdf
+
+		$ThisFileInfo['fileformat']            = 'ac3';
+		$ThisFileInfo['audio']['dataformat']   = 'ac3';
+		$ThisFileInfo['audio']['bitrate_mode'] = 'cbr';
+		$ThisFileInfo['audio']['lossless']     = false;
+
+		// An AC-3 serial coded audio bit stream is made up of a sequence of synchronization frames
+		// Each synchronization frame contains 6 coded audio blocks (AB), each of which represent 256
+		// new audio samples per channel. A synchronization information (SI) header at the beginning
+		// of each frame contains information needed to acquire and maintain synchronization. A
+		// bit stream information (BSI) header follows SI, and contains parameters describing the coded
+		// audio service. The coded audio blocks may be followed by an auxiliary data (Aux) field. At the
+		// end of each frame is an error check field that includes a CRC word for error detection. An
+		// additional CRC word is located in the SI header, the use of which, by a decoder, is optional.
+		//
+		// syncinfo() | bsi() | AB0 | AB1 | AB2 | AB3 | AB4 | AB5 | Aux | CRC
+
+		fseek($fd, $ThisFileInfo['avdataoffset'], SEEK_SET);
+		$AC3header['syncinfo'] = fread($fd, 5);
+		$thisfile_ac3_raw['synchinfo']['synchword'] = substr($AC3header['syncinfo'], 0, 2);
+
+		if ($thisfile_ac3_raw['synchinfo']['synchword'] != "\x0B\x77") {
+
+			$ThisFileInfo['error'][] = 'Expecting "\x0B\x77" at offset '.$ThisFileInfo['avdataoffset'].', found \x'.strtoupper(dechex($AC3header['syncinfo']{0})).'\x'.strtoupper(dechex($AC3header['syncinfo']{1})).' instead';
+			unset($thisfile_ac3);
+			return false;
+
+		} else {
+
+			// syncinfo() {
+			// 	 syncword    16
+			// 	 crc1        16
+			// 	 fscod        2
+			// 	 frmsizecod   6
+			// } /* end of syncinfo */
+
+			$thisfile_ac3_raw['synchinfo']['crc1']       = getid3_lib::LittleEndian2Int(substr($AC3header['syncinfo'], 2, 2));
+			$ac3_synchinfo_fscod_frmsizecod                        = getid3_lib::LittleEndian2Int(substr($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) {
+				$ThisFileInfo['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']);
+			$ThisFileInfo['audio']['bitrate'] = $thisfile_ac3['bitrate'];
+
+			$AC3header['bsi'] = getid3_lib::BigEndian2Bin(fread($fd, 15));
+			$ac3_bsi_offset = 0;
+
+			$thisfile_ac3_raw_bsi['bsid'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 5));
+			$ac3_bsi_offset += 5;
+			if ($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.
+				$ThisFileInfo['error'][] = 'Bit stream identification is version '.$thisfile_ac3_raw_bsi['bsid'].', but getID3() only understands up to version 8';
+				unset($thisfile_ac3);
+				return false;
+			}
+
+			$thisfile_ac3_raw_bsi['bsmod'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 3));
+			$ac3_bsi_offset += 3;
+			$thisfile_ac3_raw_bsi['acmod'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 3));
+			$ac3_bsi_offset += 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:
+					$ThisFileInfo['audio']['channelmode'] = 'mono';
+					break;
+				case 3:
+				case 4:
+					$ThisFileInfo['audio']['channelmode'] = 'stereo';
+					break;
+				default:
+					$ThisFileInfo['audio']['channelmode'] = 'surround';
+					break;
+			}
+			$ThisFileInfo['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.
+				$thisfile_ac3_raw_bsi['cmixlev'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 2));
+				$ac3_bsi_offset += 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.
+				$thisfile_ac3_raw_bsi['surmixlev'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 2));
+				$ac3_bsi_offset += 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.
+				$thisfile_ac3_raw_bsi['dsurmod'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 2));
+				$ac3_bsi_offset += 2;
+				$thisfile_ac3['dolby_surround_mode'] = $this->AC3dolbySurroundModeLookup($thisfile_ac3_raw_bsi['dsurmod']);
+			}
+
+			$thisfile_ac3_raw_bsi['lfeon'] = (bool) bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 1));
+			$ac3_bsi_offset += 1;
+			$thisfile_ac3['lfe_enabled'] = $thisfile_ac3_raw_bsi['lfeon'];
+			if ($thisfile_ac3_raw_bsi['lfeon']) {
+				//$ThisFileInfo['audio']['channels']++;
+				$ThisFileInfo['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.
+			$thisfile_ac3_raw_bsi['dialnorm'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 5));
+			$ac3_bsi_offset += 5;
+			$thisfile_ac3['dialogue_normalization'] = '-'.$thisfile_ac3_raw_bsi['dialnorm'].'dB';
+
+			$thisfile_ac3_raw_bsi['compre_flag'] = (bool) bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 1));
+			$ac3_bsi_offset += 1;
+			if ($thisfile_ac3_raw_bsi['compre_flag']) {
+				$thisfile_ac3_raw_bsi['compr'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 8));
+				$ac3_bsi_offset += 8;
+				$thisfile_ac3['heavy_compression'] = $this->AC3heavyCompression($thisfile_ac3_raw_bsi['compr']);
+			}
+
+			$thisfile_ac3_raw_bsi['langcode_flag'] = (bool) bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 1));
+			$ac3_bsi_offset += 1;
+			if ($thisfile_ac3_raw_bsi['langcode_flag']) {
+				$thisfile_ac3_raw_bsi['langcod'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 8));
+				$ac3_bsi_offset += 8;
+			}
+
+			$thisfile_ac3_raw_bsi['audprodie'] = (bool) bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 1));
+			$ac3_bsi_offset += 1;
+			if ($thisfile_ac3_raw_bsi['audprodie']) {
+				$thisfile_ac3_raw_bsi['mixlevel'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 5));
+				$ac3_bsi_offset += 5;
+				$thisfile_ac3_raw_bsi['roomtyp']  = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 2));
+				$ac3_bsi_offset += 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.
+				$thisfile_ac3_raw_bsi['dialnorm2'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 5));
+				$ac3_bsi_offset += 5;
+				$thisfile_ac3['dialogue_normalization2'] = '-'.$thisfile_ac3_raw_bsi['dialnorm2'].'dB';
+
+				$thisfile_ac3_raw_bsi['compre_flag2'] = (bool) bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 1));
+				$ac3_bsi_offset += 1;
+				if ($thisfile_ac3_raw_bsi['compre_flag2']) {
+					$thisfile_ac3_raw_bsi['compr2'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 8));
+					$ac3_bsi_offset += 8;
+					$thisfile_ac3['heavy_compression2'] = $this->AC3heavyCompression($thisfile_ac3_raw_bsi['compr2']);
+				}
+
+				$thisfile_ac3_raw_bsi['langcode_flag2'] = (bool) bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 1));
+				$ac3_bsi_offset += 1;
+				if ($thisfile_ac3_raw_bsi['langcode_flag2']) {
+					$thisfile_ac3_raw_bsi['langcod2'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 8));
+					$ac3_bsi_offset += 8;
+				}
+
+				$thisfile_ac3_raw_bsi['audprodie2'] = (bool) bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 1));
+				$ac3_bsi_offset += 1;
+				if ($thisfile_ac3_raw_bsi['audprodie2']) {
+					$thisfile_ac3_raw_bsi['mixlevel2'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 5));
+					$ac3_bsi_offset += 5;
+					$thisfile_ac3_raw_bsi['roomtyp2']  = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 2));
+					$ac3_bsi_offset += 2;
+
+					$thisfile_ac3['mixing_level2'] = (80 + $thisfile_ac3_raw_bsi['mixlevel2']).'dB';
+					$thisfile_ac3['room_type2']    = $this->AC3roomTypeLookup($thisfile_ac3_raw_bsi['roomtyp2']);
+				}
+
+			}
+
+			$thisfile_ac3_raw_bsi['copyright'] = (bool) bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 1));
+			$ac3_bsi_offset += 1;
+
+			$thisfile_ac3_raw_bsi['original']  = (bool) bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 1));
+			$ac3_bsi_offset += 1;
+
+			$thisfile_ac3_raw_bsi['timecode1_flag'] = (bool) bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 1));
+			$ac3_bsi_offset += 1;
+			if ($thisfile_ac3_raw_bsi['timecode1_flag']) {
+				$thisfile_ac3_raw_bsi['timecode1'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 14));
+				$ac3_bsi_offset += 14;
+			}
+
+			$thisfile_ac3_raw_bsi['timecode2_flag'] = (bool) bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 1));
+			$ac3_bsi_offset += 1;
+			if ($thisfile_ac3_raw_bsi['timecode2_flag']) {
+				$thisfile_ac3_raw_bsi['timecode2'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 14));
+				$ac3_bsi_offset += 14;
+			}
+
+			$thisfile_ac3_raw_bsi['addbsi_flag'] = (bool) bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 1));
+			$ac3_bsi_offset += 1;
+			if ($thisfile_ac3_raw_bsi['addbsi_flag']) {
+				$thisfile_ac3_raw_bsi['addbsi_length'] = bindec(substr($AC3header['bsi'], $ac3_bsi_offset, 6));
+				$ac3_bsi_offset += 6;
+
+				$AC3header['bsi'] .= getid3_lib::BigEndian2Bin(fread($fd, $thisfile_ac3_raw_bsi['addbsi_length']));
+
+				$thisfile_ac3_raw_bsi['addbsi_data'] = substr($AC3header['bsi'], $ac3_bsi_offset, $thisfile_ac3_raw_bsi['addbsi_length'] * 8);
+				$ac3_bsi_offset += $thisfile_ac3_raw_bsi['addbsi_length'] * 8;
+			}
+
+		}
+
+		return true;
+	}
+
+
+	function AC3sampleRateCodeLookup($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);
+	}
+
+	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][$acmod] : false);
+	}
+
+	function AC3audioCodingModeLookup($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);
+	}
+
+	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);
+	}
+
+	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);
+	}
+
+	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);
+	}
+
+	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 $AC3channelsEnabledLookup;
+	}
+
+	function AC3heavyCompression($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 - $lin_gain;
+	}
+
+	function AC3roomTypeLookup($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);
+	}
+
+	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][$fscod] : false);
+	}
+
+	function AC3bitrateLookup($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);
+	}
+
+
+}
+
+?>
\ No newline at end of file