module.audio.ac3.php

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<?php
//  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) {

                $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);
        }


}

?>