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<?php

/////////////////////////////////////////////////////////////////
/// getID3() by James Heinrich <info@getid3.org>               //
//  available at https://github.com/JamesHeinrich/getID3       //
//            or https://www.getid3.org                        //
//            or http://getid3.sourceforge.net                 //
//  see readme.txt for more details                            //
/////////////////////////////////////////////////////////////////
//                                                             //
// module.audio.aac.php                                        //
// module for analyzing AAC Audio files                        //
// dependencies: NONE                                          //
//                                                            ///
/////////////////////////////////////////////////////////////////

if (!defined('GETID3_INCLUDEPATH')) { // prevent path-exposing attacks that access modules directly on public webservers
    exit;
}

class getid3_aac extends getid3_handler
{
    /**
     * @return bool
     */
    public function Analyze() {
        $info = &$this->getid3->info;
        $this->fseek($info['avdataoffset']);
        if ($this->fread(4) == 'ADIF') {
            $this->getAACADIFheaderFilepointer();
        } else {
            $this->getAACADTSheaderFilepointer();
        }
        return true;
    }

    /**
     * @return bool
     */
    public function getAACADIFheaderFilepointer() {
        $info = &$this->getid3->info;
        $info['fileformat']          = 'aac';
        $info['audio']['dataformat'] = 'aac';
        $info['audio']['lossless']   = false;

        $this->fseek($info['avdataoffset']);
        $AACheader = $this->fread(1024);
        $offset    = 0;

        if (substr($AACheader, 0, 4) == 'ADIF') {

            // http://faac.sourceforge.net/wiki/index.php?page=ADIF

            // http://libmpeg.org/mpeg4/doc/w2203tfs.pdf
            // adif_header() {
            //     adif_id                                32
            //     copyright_id_present                    1
            //     if( copyright_id_present )
            //         copyright_id                       72
            //     original_copy                           1
            //     home                                    1
            //     bitstream_type                          1
            //     bitrate                                23
            //     num_program_config_elements             4
            //     for (i = 0; i < num_program_config_elements + 1; i++ ) {
            //         if( bitstream_type == '0' )
            //             adif_buffer_fullness           20
            //         program_config_element()
            //     }
            // }

            $AACheaderBitstream = getid3_lib::BigEndian2Bin($AACheader);
            $bitoffset          = 0;

            $info['aac']['header_type']                   = 'ADIF';
            $bitoffset += 32;
            $info['aac']['header']['mpeg_version']        = 4;

            $info['aac']['header']['copyright']           = substr($AACheaderBitstream, $bitoffset, 1) == '1';
            $bitoffset += 1;
            if ($info['aac']['header']['copyright']) {
                $info['aac']['header']['copyright_id']    = getid3_lib::Bin2String(substr($AACheaderBitstream, $bitoffset, 72));
                $bitoffset += 72;
            }
            $info['aac']['header']['original_copy']       = substr($AACheaderBitstream, $bitoffset, 1) == '1';
            $bitoffset += 1;
            $info['aac']['header']['home']                = substr($AACheaderBitstream, $bitoffset, 1) == '1';
            $bitoffset += 1;
            $info['aac']['header']['is_vbr']              = substr($AACheaderBitstream, $bitoffset, 1) == '1';
            $bitoffset += 1;
            if ($info['aac']['header']['is_vbr']) {
                $info['audio']['bitrate_mode']            = 'vbr';
                $info['aac']['header']['bitrate_max']     = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 23));
                $bitoffset += 23;
            } else {
                $info['audio']['bitrate_mode']            = 'cbr';
                $info['aac']['header']['bitrate']         = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 23));
                $bitoffset += 23;
                $info['audio']['bitrate']                 = $info['aac']['header']['bitrate'];
            }
            if ($info['audio']['bitrate'] == 0) {
                $this->error('Corrupt AAC file: bitrate_audio == zero');
                return false;
            }
            $info['aac']['header']['num_program_configs'] = 1 + getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 4));
            $bitoffset += 4;

            for ($i = 0; $i < $info['aac']['header']['num_program_configs']; $i++) {
                // http://www.audiocoding.com/wiki/index.php?page=program_config_element

                // buffer_fullness                       20

                // element_instance_tag                   4
                // object_type                            2
                // sampling_frequency_index               4
                // num_front_channel_elements             4
                // num_side_channel_elements              4
                // num_back_channel_elements              4
                // num_lfe_channel_elements               2
                // num_assoc_data_elements                3
                // num_valid_cc_elements                  4
                // mono_mixdown_present                   1
                // mono_mixdown_element_number            4   if mono_mixdown_present == 1
                // stereo_mixdown_present                 1
                // stereo_mixdown_element_number          4   if stereo_mixdown_present == 1
                // matrix_mixdown_idx_present             1
                // matrix_mixdown_idx                     2   if matrix_mixdown_idx_present == 1
                // pseudo_surround_enable                 1   if matrix_mixdown_idx_present == 1
                // for (i = 0; i < num_front_channel_elements; i++) {
                //     front_element_is_cpe[i]            1
                //     front_element_tag_select[i]        4
                // }
                // for (i = 0; i < num_side_channel_elements; i++) {
                //     side_element_is_cpe[i]             1
                //     side_element_tag_select[i]         4
                // }
                // for (i = 0; i < num_back_channel_elements; i++) {
                //     back_element_is_cpe[i]             1
                //     back_element_tag_select[i]         4
                // }
                // for (i = 0; i < num_lfe_channel_elements; i++) {
                //     lfe_element_tag_select[i]          4
                // }
                // for (i = 0; i < num_assoc_data_elements; i++) {
                //     assoc_data_element_tag_select[i]   4
                // }
                // for (i = 0; i < num_valid_cc_elements; i++) {
                //     cc_element_is_ind_sw[i]            1
                //     valid_cc_element_tag_select[i]     4
                // }
                // byte_alignment()                       VAR
                // comment_field_bytes                    8
                // for (i = 0; i < comment_field_bytes; i++) {
                //     comment_field_data[i]              8
                // }

                if (!$info['aac']['header']['is_vbr']) {
                    $info['aac']['program_configs'][$i]['buffer_fullness']        = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 20));
                    $bitoffset += 20;
                }
                $info['aac']['program_configs'][$i]['element_instance_tag']       = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 4));
                $bitoffset += 4;
                $info['aac']['program_configs'][$i]['object_type']                = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 2));
                $bitoffset += 2;
                $info['aac']['program_configs'][$i]['sampling_frequency_index']   = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 4));
                $bitoffset += 4;
                $info['aac']['program_configs'][$i]['num_front_channel_elements'] = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 4));
                $bitoffset += 4;
                $info['aac']['program_configs'][$i]['num_side_channel_elements']  = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 4));
                $bitoffset += 4;
                $info['aac']['program_configs'][$i]['num_back_channel_elements']  = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 4));
                $bitoffset += 4;
                $info['aac']['program_configs'][$i]['num_lfe_channel_elements']   = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 2));
                $bitoffset += 2;
                $info['aac']['program_configs'][$i]['num_assoc_data_elements']    = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 3));
                $bitoffset += 3;
                $info['aac']['program_configs'][$i]['num_valid_cc_elements']      = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 4));
                $bitoffset += 4;
                $info['aac']['program_configs'][$i]['mono_mixdown_present']       = (bool) getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 1));
                $bitoffset += 1;
                if ($info['aac']['program_configs'][$i]['mono_mixdown_present']) {
                    $info['aac']['program_configs'][$i]['mono_mixdown_element_number']    = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 4));
                    $bitoffset += 4;
                }
                $info['aac']['program_configs'][$i]['stereo_mixdown_present']             = (bool) getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 1));
                $bitoffset += 1;
                if ($info['aac']['program_configs'][$i]['stereo_mixdown_present']) {
                    $info['aac']['program_configs'][$i]['stereo_mixdown_element_number']  = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 4));
                    $bitoffset += 4;
                }
                $info['aac']['program_configs'][$i]['matrix_mixdown_idx_present']         = (bool) getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 1));
                $bitoffset += 1;
                if ($info['aac']['program_configs'][$i]['matrix_mixdown_idx_present']) {
                    $info['aac']['program_configs'][$i]['matrix_mixdown_idx']             = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 2));
                    $bitoffset += 2;
                    $info['aac']['program_configs'][$i]['pseudo_surround_enable']         = (bool) getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 1));
                    $bitoffset += 1;
                }
                for ($j = 0; $j < $info['aac']['program_configs'][$i]['num_front_channel_elements']; $j++) {
                    $info['aac']['program_configs'][$i]['front_element_is_cpe'][$j]     = (bool) getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 1));
                    $bitoffset += 1;
                    $info['aac']['program_configs'][$i]['front_element_tag_select'][$j] = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 4));
                    $bitoffset += 4;
                }
                for ($j = 0; $j < $info['aac']['program_configs'][$i]['num_side_channel_elements']; $j++) {
                    $info['aac']['program_configs'][$i]['side_element_is_cpe'][$j]     = (bool) getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 1));
                    $bitoffset += 1;
                    $info['aac']['program_configs'][$i]['side_element_tag_select'][$j] = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 4));
                    $bitoffset += 4;
                }
                for ($j = 0; $j < $info['aac']['program_configs'][$i]['num_back_channel_elements']; $j++) {
                    $info['aac']['program_configs'][$i]['back_element_is_cpe'][$j]     = (bool) getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 1));
                    $bitoffset += 1;
                    $info['aac']['program_configs'][$i]['back_element_tag_select'][$j] = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 4));
                    $bitoffset += 4;
                }
                for ($j = 0; $j < $info['aac']['program_configs'][$i]['num_lfe_channel_elements']; $j++) {
                    $info['aac']['program_configs'][$i]['lfe_element_tag_select'][$j] = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 4));
                    $bitoffset += 4;
                }
                for ($j = 0; $j < $info['aac']['program_configs'][$i]['num_assoc_data_elements']; $j++) {
                    $info['aac']['program_configs'][$i]['assoc_data_element_tag_select'][$j] = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 4));
                    $bitoffset += 4;
                }
                for ($j = 0; $j < $info['aac']['program_configs'][$i]['num_valid_cc_elements']; $j++) {
                    $info['aac']['program_configs'][$i]['cc_element_is_ind_sw'][$j]          = (bool) getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 1));
                    $bitoffset += 1;
                    $info['aac']['program_configs'][$i]['valid_cc_element_tag_select'][$j]   = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 4));
                    $bitoffset += 4;
                }

                $bitoffset = ceil($bitoffset / 8) * 8;

                $info['aac']['program_configs'][$i]['comment_field_bytes'] = getid3_lib::Bin2Dec(substr($AACheaderBitstream, $bitoffset, 8));
                $bitoffset += 8;
                $info['aac']['program_configs'][$i]['comment_field']       = getid3_lib::Bin2String(substr($AACheaderBitstream, $bitoffset, 8 * $info['aac']['program_configs'][$i]['comment_field_bytes']));
                $bitoffset += 8 * $info['aac']['program_configs'][$i]['comment_field_bytes'];


                $info['aac']['header']['profile']                           = self::AACprofileLookup($info['aac']['program_configs'][$i]['object_type'], $info['aac']['header']['mpeg_version']);
                $info['aac']['program_configs'][$i]['sampling_frequency']   = self::AACsampleRateLookup($info['aac']['program_configs'][$i]['sampling_frequency_index']);
                $info['audio']['sample_rate']                               = $info['aac']['program_configs'][$i]['sampling_frequency'];
                $info['audio']['channels']                                  = self::AACchannelCountCalculate($info['aac']['program_configs'][$i]);
                if ($info['aac']['program_configs'][$i]['comment_field']) {
                    $info['aac']['comments'][]                          = $info['aac']['program_configs'][$i]['comment_field'];
                }
            }
            $info['playtime_seconds'] = (($info['avdataend'] - $info['avdataoffset']) * 8) / $info['audio']['bitrate'];

            $info['audio']['encoder_options'] = $info['aac']['header_type'].' '.$info['aac']['header']['profile'];



            return true;

        } else {

            unset($info['fileformat']);
            unset($info['aac']);
            $this->error('AAC-ADIF synch not found at offset '.$info['avdataoffset'].' (expected "ADIF", found "'.substr($AACheader, 0, 4).'" instead)');
            return false;

        }

    }

    /**
     * @param int  $MaxFramesToScan
     * @param bool $ReturnExtendedInfo
     *
     * @return bool
     */
    public function getAACADTSheaderFilepointer($MaxFramesToScan=1000000, $ReturnExtendedInfo=false) {
        $info = &$this->getid3->info;

        // based loosely on code from AACfile by Jurgen Faul  <jfaulØgmx.de>
        // http://jfaul.de/atl  or  http://j-faul.virtualave.net/atl/atl.html


        // http://faac.sourceforge.net/wiki/index.php?page=ADTS // dead link
        // http://wiki.multimedia.cx/index.php?title=ADTS

        // * ADTS Fixed Header: these don't change from frame to frame
        // syncword                                       12    always: '111111111111'
        // ID                                              1    0: MPEG-4, 1: MPEG-2
        // MPEG layer                                      2    If you send AAC in MPEG-TS, set to 0
        // protection_absent                               1    0: CRC present; 1: no CRC
        // profile                                         2    0: AAC Main; 1: AAC LC (Low Complexity); 2: AAC SSR (Scalable Sample Rate); 3: AAC LTP (Long Term Prediction)
        // sampling_frequency_index                        4    15 not allowed
        // private_bit                                     1    usually 0
        // channel_configuration                           3
        // original/copy                                   1    0: original; 1: copy
        // home                                            1    usually 0
        // emphasis                                        2    only if ID == 0 (ie MPEG-4)  // not present in some documentation?

        // * ADTS Variable Header: these can change from frame to frame
        // copyright_identification_bit                    1
        // copyright_identification_start                  1
        // aac_frame_length                               13    length of the frame including header (in bytes)
        // adts_buffer_fullness                           11    0x7FF indicates VBR
        // no_raw_data_blocks_in_frame                     2

        // * ADTS Error check
        // crc_check                                      16    only if protection_absent == 0

        $byteoffset  = $info['avdataoffset'];
        $framenumber = 0;

        // Init bit pattern array
        static $decbin = array();

        // Populate $bindec
        for ($i = 0; $i < 256; $i++) {
            $decbin[chr($i)] = str_pad(decbin($i), 8, '0', STR_PAD_LEFT);
        }

        // used to calculate bitrate below
        $BitrateCache = array();


        while (true) {
            // breaks out when end-of-file encountered, or invalid data found,
            // or MaxFramesToScan frames have been scanned

            if (!getid3_lib::intValueSupported($byteoffset)) {
                $this->warning('Unable to parse AAC file beyond '.$this->ftell().' (PHP does not support file operations beyond '.round(PHP_INT_MAX / 1073741824).'GB)');
                return false;
            }
            $this->fseek($byteoffset);

            // First get substring
            $substring = $this->fread(9); // header is 7 bytes (or 9 if CRC is present)
            $substringlength = strlen($substring);
            if ($substringlength != 9) {
                $this->error('Failed to read 7 bytes at offset '.($this->ftell() - $substringlength).' (only read '.$substringlength.' bytes)');
                return false;
            }
            // this would be easier with 64-bit math, but split it up to allow for 32-bit:
            $header1 = getid3_lib::BigEndian2Int(substr($substring, 0, 2));
            $header2 = getid3_lib::BigEndian2Int(substr($substring, 2, 4));
            $header3 = getid3_lib::BigEndian2Int(substr($substring, 6, 1));

            $info['aac']['header']['raw']['syncword']          = ($header1 & 0xFFF0) >> 4;
            if ($info['aac']['header']['raw']['syncword'] != 0x0FFF) {
                $this->error('Synch pattern (0x0FFF) not found at offset '.($this->ftell() - $substringlength).' (found 0x0'.strtoupper(dechex($info['aac']['header']['raw']['syncword'])).' instead)');
                //if ($info['fileformat'] == 'aac') {
                //  return true;
                //}
                unset($info['aac']);
                return false;
            }

            // Gather info for first frame only - this takes time to do 1000 times!
            if ($framenumber == 0) {
                $info['aac']['header_type']                      = 'ADTS';
                $info['fileformat']                              = 'aac';
                $info['audio']['dataformat']                     = 'aac';

                $info['aac']['header']['raw']['mpeg_version']      = ($header1 & 0x0008) >> 3;
                $info['aac']['header']['raw']['mpeg_layer']        = ($header1 & 0x0006) >> 1;
                $info['aac']['header']['raw']['protection_absent'] = ($header1 & 0x0001) >> 0;

                $info['aac']['header']['raw']['profile_code']      = ($header2 & 0xC0000000) >> 30;
                $info['aac']['header']['raw']['sample_rate_code']  = ($header2 & 0x3C000000) >> 26;
                $info['aac']['header']['raw']['private_stream']    = ($header2 & 0x02000000) >> 25;
                $info['aac']['header']['raw']['channels_code']     = ($header2 & 0x01C00000) >> 22;
                $info['aac']['header']['raw']['original']          = ($header2 & 0x00200000) >> 21;
                $info['aac']['header']['raw']['home']              = ($header2 & 0x00100000) >> 20;
                $info['aac']['header']['raw']['copyright_stream']  = ($header2 & 0x00080000) >> 19;
                $info['aac']['header']['raw']['copyright_start']   = ($header2 & 0x00040000) >> 18;
                $info['aac']['header']['raw']['frame_length']      = ($header2 & 0x0003FFE0) >>  5;

                $info['aac']['header']['mpeg_version']     = ($info['aac']['header']['raw']['mpeg_version']      ? 2    : 4);
                $info['aac']['header']['crc_present']      = ($info['aac']['header']['raw']['protection_absent'] ? false: true);
                $info['aac']['header']['profile']          = self::AACprofileLookup($info['aac']['header']['raw']['profile_code'], $info['aac']['header']['mpeg_version']);
                $info['aac']['header']['sample_frequency'] = self::AACsampleRateLookup($info['aac']['header']['raw']['sample_rate_code']);
                $info['aac']['header']['private']          = (bool) $info['aac']['header']['raw']['private_stream'];
                $info['aac']['header']['original']         = (bool) $info['aac']['header']['raw']['original'];
                $info['aac']['header']['home']             = (bool) $info['aac']['header']['raw']['home'];
                $info['aac']['header']['channels']         = (($info['aac']['header']['raw']['channels_code'] == 7) ? 8 : $info['aac']['header']['raw']['channels_code']);
                if ($ReturnExtendedInfo) {
                    $info['aac'][$framenumber]['copyright_id_bit']   = (bool) $info['aac']['header']['raw']['copyright_stream'];
                    $info['aac'][$framenumber]['copyright_id_start'] = (bool) $info['aac']['header']['raw']['copyright_start'];
                }

                if ($info['aac']['header']['raw']['mpeg_layer'] != 0) {
                    $this->warning('Layer error - expected "0", found "'.$info['aac']['header']['raw']['mpeg_layer'].'" instead');
                }
                if ($info['aac']['header']['sample_frequency'] == 0) {
                    $this->error('Corrupt AAC file: sample_frequency == zero');
                    return false;
                }

                $info['audio']['sample_rate'] = $info['aac']['header']['sample_frequency'];
                $info['audio']['channels']    = $info['aac']['header']['channels'];
            }

            $FrameLength = ($header2 & 0x0003FFE0) >>  5;

            if (!isset($BitrateCache[$FrameLength])) {
                $BitrateCache[$FrameLength] = ($info['aac']['header']['sample_frequency'] / 1024) * $FrameLength * 8;
            }
            getid3_lib::safe_inc($info['aac']['bitrate_distribution'][$BitrateCache[$FrameLength]], 1);

            $info['aac'][$framenumber]['aac_frame_length']     = $FrameLength;

            $info['aac'][$framenumber]['adts_buffer_fullness'] = (($header2 & 0x0000001F) << 6) & (($header3 & 0xFC) >> 2);
            if ($info['aac'][$framenumber]['adts_buffer_fullness'] == 0x07FF) {
                $info['audio']['bitrate_mode'] = 'vbr';
            } else {
                $info['audio']['bitrate_mode'] = 'cbr';
            }
            $info['aac'][$framenumber]['num_raw_data_blocks']  = (($header3 & 0x03) >> 0);

            if ($info['aac']['header']['crc_present']) {
                //$info['aac'][$framenumber]['crc'] = getid3_lib::BigEndian2Int(substr($substring, 7, 2);
            }

            if (!$ReturnExtendedInfo) {
                unset($info['aac'][$framenumber]);
            }

            /*
            $rounded_precision = 5000;
            $info['aac']['bitrate_distribution_rounded'] = array();
            foreach ($info['aac']['bitrate_distribution'] as $bitrate => $count) {
                $rounded_bitrate = round($bitrate / $rounded_precision) * $rounded_precision;
                getid3_lib::safe_inc($info['aac']['bitrate_distribution_rounded'][$rounded_bitrate], $count);
            }
            ksort($info['aac']['bitrate_distribution_rounded']);
            */

            $byteoffset += $FrameLength;
            if ((++$framenumber < $MaxFramesToScan) && (($byteoffset + 10) < $info['avdataend'])) {

                // keep scanning

            } else {

                $info['aac']['frames']    = $framenumber;
                $info['playtime_seconds'] = ($info['avdataend'] / $byteoffset) * (($framenumber * 1024) / $info['aac']['header']['sample_frequency']);  // (1 / % of file scanned) * (samples / (samples/sec)) = seconds
                if ($info['playtime_seconds'] == 0) {
                    $this->error('Corrupt AAC file: playtime_seconds == zero');
                    return false;
                }
                $info['audio']['bitrate']    = (($info['avdataend'] - $info['avdataoffset']) * 8) / $info['playtime_seconds'];
                ksort($info['aac']['bitrate_distribution']);

                $info['audio']['encoder_options'] = $info['aac']['header_type'].' '.$info['aac']['header']['profile'];

                return true;

            }
        }
        // should never get here.
    }

    /**
     * @param int $samplerateid
     *
     * @return int|string
     */
    public static function AACsampleRateLookup($samplerateid) {
        static $AACsampleRateLookup = array();
        if (empty($AACsampleRateLookup)) {
            $AACsampleRateLookup[0]  = 96000;
            $AACsampleRateLookup[1]  = 88200;
            $AACsampleRateLookup[2]  = 64000;
            $AACsampleRateLookup[3]  = 48000;
            $AACsampleRateLookup[4]  = 44100;
            $AACsampleRateLookup[5]  = 32000;
            $AACsampleRateLookup[6]  = 24000;
            $AACsampleRateLookup[7]  = 22050;
            $AACsampleRateLookup[8]  = 16000;
            $AACsampleRateLookup[9]  = 12000;
            $AACsampleRateLookup[10] = 11025;
            $AACsampleRateLookup[11] = 8000;
            $AACsampleRateLookup[12] = 0;
            $AACsampleRateLookup[13] = 0;
            $AACsampleRateLookup[14] = 0;
            $AACsampleRateLookup[15] = 0;
        }
        return (isset($AACsampleRateLookup[$samplerateid]) ? $AACsampleRateLookup[$samplerateid] : 'invalid');
    }

    /**
     * @param int $profileid
     * @param int $mpegversion
     *
     * @return string
     */
    public static function AACprofileLookup($profileid, $mpegversion) {
        static $AACprofileLookup = array();
        if (empty($AACprofileLookup)) {
            $AACprofileLookup[2][0]  = 'Main profile';
            $AACprofileLookup[2][1]  = 'Low Complexity profile (LC)';
            $AACprofileLookup[2][2]  = 'Scalable Sample Rate profile (SSR)';
            $AACprofileLookup[2][3]  = '(reserved)';
            $AACprofileLookup[4][0]  = 'AAC_MAIN';
            $AACprofileLookup[4][1]  = 'AAC_LC';
            $AACprofileLookup[4][2]  = 'AAC_SSR';
            $AACprofileLookup[4][3]  = 'AAC_LTP';
        }
        return (isset($AACprofileLookup[$mpegversion][$profileid]) ? $AACprofileLookup[$mpegversion][$profileid] : 'invalid');
    }

    /**
     * @param array $program_configs
     *
     * @return int
     */
    public static function AACchannelCountCalculate($program_configs) {
        $channels = 0;
        for ($i = 0; $i < $program_configs['num_front_channel_elements']; $i++) {
            $channels++;
            if ($program_configs['front_element_is_cpe'][$i]) {
                // each front element is channel pair (CPE = Channel Pair Element)
                $channels++;
            }
        }
        for ($i = 0; $i < $program_configs['num_side_channel_elements']; $i++) {
            $channels++;
            if ($program_configs['side_element_is_cpe'][$i]) {
                // each side element is channel pair (CPE = Channel Pair Element)
                $channels++;
            }
        }
        for ($i = 0; $i < $program_configs['num_back_channel_elements']; $i++) {
            $channels++;
            if ($program_configs['back_element_is_cpe'][$i]) {
                // each back element is channel pair (CPE = Channel Pair Element)
                $channels++;
            }
        }
        for ($i = 0; $i < $program_configs['num_lfe_channel_elements']; $i++) {
            $channels++;
        }
        return $channels;
    }

}