Ac3.php

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<?php
 
namespace GetId3\Module\Audio;
 
use GetId3\Handler\BaseHandler;
use GetId3\Lib\Helper;
 
//  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 Ac3 extends BaseHandler
{
    private $AC3header = array();
 
    private $BSIoffset = 0;
 
    public function analyze()
    {
        $info = &$this->getid3->info;
 
        $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);
 
        $magic = "\x0B\x77";
 
        if (strpos($this->AC3header['syncinfo'], $magic) === 0) {
            $thisfile_ac3_raw['synchinfo']['synchword'] = $magic;
            $offset = 2;
        } else {
            if (!$this->isDependencyFor('matroska')) {
                unset($info['fileformat'], $info['ac3']);
 
                return $this->error('Expecting "'.Helper::PrintHexBytes($magic).'" at offset '.$info['avdataoffset'].', found "'.Helper::PrintHexBytes(substr($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;
 
        $thisfile_ac3_raw['synchinfo']['crc1']       = Helper::LittleEndian2Int(substr($this->AC3header['syncinfo'], $offset, 2));
        $ac3_synchinfo_fscod_frmsizecod              = Helper::LittleEndian2Int(substr($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'];
 
        $this->AC3header['bsi'] = Helper::BigEndian2Bin($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 GetId3Core() 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);
 
            $this->AC3header['bsi'] .= Helper::BigEndian2Bin($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 $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 serviceTypeLookup($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 audioCodingModeLookup($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 centerMixLevelLookup($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 surroundMixLevelLookup($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 dolbySurroundModeLookup($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 channelsEnabledLookup($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 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) * Helper::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 $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 frameSizeLookup($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 bitrateLookup($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);
    }
}