Calculate the duration of an mp3 file using PHP

On a website where you upload an mp3 file, it is often useful to have a class that can analyze that mp3 file, extract some meta data about bitrate, song length, etc.

This was written in PHP5, and won't work on PHP4 web servers. Using this PHP class we can analyze an mp3 file and determine if it has a constant bitrate or a variable bitrate (CBR vs VBR), and determine its length, its bitrate (128 is common) and other data stored in the mp3 frame header.


mp3file.php (PHP Class)

<?php
class MP3File
{
    protected $filename;
    public function __construct($filename)
    {
        $this->filename = $filename;
    }
 
    public static function formatTime($duration)
    {
        $hours = floor($duration / 3600);
        $minutes = floor( ($duration - ($hours * 3600)) / 60);
        $seconds = $duration - ($hours * 3600) - ($minutes * 60);
        return sprintf("%02d:%02d:%02d", $hours, $minutes, $seconds);
    }
 
    public function getDurationEstimate()
    {
        return $this->getDuration($use_cbr_estimate=true);
    }
 
    public function getDuration($use_cbr_estimate=false)
    {
        $fd = fopen($this->filename, "rb");
 
        $duration=0;
        $block = fread($fd, 100);
        $offset = $this->skipID3v2Tag($block);
        fseek($fd, $offset, SEEK_SET);
        while (!feof($fd))
        {
            $block = fread($fd, 10);
            if (strlen($block)<10) { break; }
            else if ($block[0]=="\xff" && (ord($block[1])&0xe0) )
            {
                $info = self::parseFrameHeader(substr($block, 0, 4));
                if (empty($info['Framesize'])) { return $duration; } 
                fseek($fd, $info['Framesize']-10, SEEK_CUR);
                $duration += ( $info['Samples'] / $info['Sampling Rate'] );
            }
            else if (substr($block, 0, 3)=='TAG')
            {
                fseek($fd, 128-10, SEEK_CUR);
            }
            else
            {
                fseek($fd, -9, SEEK_CUR);
            }
            if ($use_cbr_estimate && !empty($info))
            { 
                return $this->estimateDuration($info['Bitrate'],$offset); 
            }
        }
        return round($duration);
    }
 
    private function estimateDuration($bitrate,$offset)
    {
        $kbps = ($bitrate*1000)/8;
        $datasize = filesize($this->filename) - $offset;
        return round($datasize / $kbps);
    }
 
    private function skipID3v2Tag(&$block)
    {
        if (substr($block, 0,3)=="ID3")
        {
            $id3v2_major_version = ord($block[3]);
            $id3v2_minor_version = ord($block[4]);
            $id3v2_flags = ord($block[5]);
            $flag_unsynchronisation  = $id3v2_flags & 0x80 ? 1 : 0;
            $flag_extended_header    = $id3v2_flags & 0x40 ? 1 : 0;
            $flag_experimental_ind   = $id3v2_flags & 0x20 ? 1 : 0;
            $flag_footer_present     = $id3v2_flags & 0x10 ? 1 : 0;
            $z0 = ord($block[6]);
            $z1 = ord($block[7]);
            $z2 = ord($block[8]);
            $z3 = ord($block[9]);
            if ( (($z0&0x80)==0) && (($z1&0x80)==0) && (($z2&0x80)==0) && (($z3&0x80)==0) )
            {
                $header_size = 10;
                $tag_size = (($z0&0x7f) * 2097152) + (($z1&0x7f) * 16384) + (($z2&0x7f) * 128) + ($z3&0x7f);
                $footer_size = $flag_footer_present ? 10 : 0;
                return $header_size + $tag_size + $footer_size;
            }
        }
        return 0;
    }
 
    public static function parseFrameHeader($fourbytes)
    {
        static $versions = array(
            0x0=>'2.5',0x1=>'x',0x2=>'2',0x3=>'1',
        );
        static $layers = array(
            0x0=>'x',0x1=>'3',0x2=>'2',0x3=>'1',
        );
        static $bitrates = array(
            'V1L1'=>array(0,32,64,96,128,160,192,224,256,288,320,352,384,416,448),
            'V1L2'=>array(0,32,48,56, 64, 80, 96,112,128,160,192,224,256,320,384),
            'V1L3'=>array(0,32,40,48, 56, 64, 80, 96,112,128,160,192,224,256,320),
            'V2L1'=>array(0,32,48,56, 64, 80, 96,112,128,144,160,176,192,224,256),
            'V2L2'=>array(0, 8,16,24, 32, 40, 48, 56, 64, 80, 96,112,128,144,160),
            'V2L3'=>array(0, 8,16,24, 32, 40, 48, 56, 64, 80, 96,112,128,144,160),
        );
        static $sample_rates = array(
            '1'   => array(44100,48000,32000),
            '2'   => array(22050,24000,16000),
            '2.5' => array(11025,12000, 8000),
        );
        static $samples = array(
            1 => array( 1 => 384, 2 =>1152, 3 =>1152, ),
            2 => array( 1 => 384, 2 =>1152, 3 => 576, ),
        );
        $b1=ord($fourbytes[1]);
        $b2=ord($fourbytes[2]);
        $b3=ord($fourbytes[3]);
 
        $version_bits = ($b1 & 0x18) >> 3;
        $version = $versions[$version_bits];
        $simple_version =  ($version=='2.5' ? 2 : $version);
 
        $layer_bits = ($b1 & 0x06) >> 1;
        $layer = $layers[$layer_bits];
 
        $protection_bit = ($b1 & 0x01);
        $bitrate_key = sprintf('V%dL%d', $simple_version , $layer);
        $bitrate_idx = ($b2 & 0xf0) >> 4;
        $bitrate = isset($bitrates[$bitrate_key][$bitrate_idx]) ? $bitrates[$bitrate_key][$bitrate_idx] : 0;
 
        $sample_rate_idx = ($b2 & 0x0c) >> 2;
        $sample_rate = isset($sample_rates[$version][$sample_rate_idx]) ? $sample_rates[$version][$sample_rate_idx] : 0;
        $padding_bit = ($b2 & 0x02) >> 1;
        $private_bit = ($b2 & 0x01);
        $channel_mode_bits = ($b3 & 0xc0) >> 6;
        $mode_extension_bits = ($b3 & 0x30) >> 4;
        $copyright_bit = ($b3 & 0x08) >> 3;
        $original_bit = ($b3 & 0x04) >> 2;
        $emphasis = ($b3 & 0x03);
 
        $info = array();
        $info['Version'] = $version;
        $info['Layer'] = $layer;
        //$info['Protection Bit'] = $protection_bit;
        $info['Bitrate'] = $bitrate;
        $info['Sampling Rate'] = $sample_rate;
        //$info['Padding Bit'] = $padding_bit;
        //$info['Private Bit'] = $private_bit;
        //$info['Channel Mode'] = $channel_mode_bits;
        //$info['Mode Extension'] = $mode_extension_bits;
        //$info['Copyright'] = $copyright_bit;
        //$info['Original'] = $original_bit;
        //$info['Emphasis'] = $emphasis;
        $info['Framesize'] = self::framesize($layer, $bitrate, $sample_rate, $padding_bit);
        $info['Samples'] = $samples[$simple_version][$layer];
        return $info;
    }
 
    private static function framesize($layer, $bitrate,$sample_rate,$padding_bit)
    {
        if ($layer==1)
            return intval(((12 * $bitrate*1000 /$sample_rate) + $padding_bit) * 4);
        else //layer 2, 3
            return intval(((144 * $bitrate*1000)/$sample_rate) + $padding_bit);
    }
}
?>

Using this class:

<?php
$mp3file = new MP3File("shook_ones.mp3");
$duration1 = $mp3file->getDurationEstimate();
$duration2 = $mp3file->getDuration();
echo "Duration: $duration1 seconds"."<br/>";
echo "Estimate: $duration2 seconds"."<br/>";
echo MP3File::formatTime($duration2)."<br/>";
?>

Output is something like:

    Duration: 326 seconds
    Estimate: 326 seconds
    00:5:26

That's all.