PHP Calculate Duration of MP3

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

This was written in PHP5, and will not 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. For reference http://www.mp3-tech.org/programmer/frame_header.html was used as an mp3 frame spec.

[edit 2014-11-30: updated code to improve VBR support, improve CBR accuracy]

sample usage:

<?php
$mp3file = new MP3File("npr_304314290.mp3");//http://www.npr.org/rss/podcast.php?id=510282
$duration1 = $mp3file->getDurationEstimate();//(faster) for CBR only
$duration2 = $mp3file->getDuration();//(slower) for VBR (or CBR)
echo "duration: $duration1 seconds"."\n";
echo "estimate: $duration2 seconds"."\n";
echo MP3File::formatTime($duration2)."\n";
?>

sample output:

duration: 2902 seconds
estimate: 2902 seconds
00:48:22

mp3file.class.php

<?php
class MP3File
{
    protected $filename;
    public function __construct($filename)
    {
        $this->filename = $filename;
    }
 
    public static function formatTime($duration) //as hh:mm:ss
    {
        //return sprintf("%d:%02d", $duration/60, $duration%60);
        $hours = floor($duration / 3600);
        $minutes = floor( ($duration - ($hours * 3600)) / 60);
        $seconds = $duration - ($hours * 3600) - ($minutes * 60);
        return sprintf("%02d:%02d:%02d", $hours, $minutes, $seconds);
    }
 
    //Read first mp3 frame only...  use for CBR constant bit rate MP3s
    public function getDurationEstimate()
    {
        return $this->getDuration($use_cbr_estimate=true);
    }
 
    //Read entire file, frame by frame... ie: Variable Bit Rate (VBR)
    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($block)<10) { break; }
            //looking for 1111 1111 111 (frame synchronization bits)
            else if ($block[0]=="\xff" && (ord($block[1])&0xe0) )
            {
                $info = self::parseFrameHeader(substr($block, 0, 4));
                if (empty($info['Framesize'])) { return $duration; } //some corrupt mp3 files
                fseek($fd, $info['Framesize']-10, SEEK_CUR);
                $duration += ( $info['Samples'] / $info['Sampling Rate'] );
            }
            else if (substr($block, 0, 3)=='TAG')
            {
                fseek($fd, 128-10, SEEK_CUR);//skip over id3v1 tag size
            }
            else
            {
                fseek($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;//bytes to skip
            }
        }
        return 0;
    }
 
    public static function parseFrameHeader($fourbytes)
    {
        static $versions = array(
            0x0=>'2.5',0x1=>'x',0x2=>'2',0x3=>'1', // x=>'reserved'
        );
        static $layers = array(
            0x0=>'x',0x1=>'3',0x2=>'2',0x3=>'1', // x=>'reserved'
        );
        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 $samples = array(
            1 => array( 1 => 384, 2 =>1152, 3 =>1152, ), //MPEGv1,     Layers 1,2,3
            2 => array( 1 => 384, 2 =>1152, 3 => 576, ), //MPEGv2/2.5, Layers 1,2,3
        );
        //$b0=ord($fourbytes[0]);//will always be 0xff
        $b1=ord($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;//0xc => b1100
        $sample_rate = isset($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;//MPEGVersion
        $info['Layer'] = $layer;
        //$info['Protection Bit'] = $protection_bit; //0=> protected by 2 byte CRC, 1=>not protected
        $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);
    }
}

code snippets are licensed under Creative Commons CC-By-SA 3.0 (unless otherwise specified)

Angus on 2009-11-30 07:18:05

Great class, just what I was looking for
Thank you.

Shapu on 2010-01-14 17:14:49

Very usefull
Thanks alot !!

Barry Carlyon on 2010-02-17 14:40:29

Saves using the massive mp3 id3tag library I currently use for getting and setting tags.
Especially when all I'm after is the mp3 length...

Ravi on 2010-07-17 12:38:08

Hey Great work! Thanks for sharing.

Abhishek on 2010-08-31 21:24:04

Very useful and precise code..thanks a lot

Ravindra on 2010-10-01 09:24:47

Great Thanks. It is so handy class. till today I have used FFMPEG for to get the mp3 song duration.

DeQyd on 2010-11-24 23:33:20

maaad respect!

Jorge on 2013-09-11 08:05:07

Fantastic !! thank you very much !!

Charles on 2013-07-05 08:13:54

Very nice. I tried it and it worked out of the box. Thank you and God bless you

nguyenung on 2014-02-08 02:32:42

Thank you :)

developer on 2014-02-10 10:43:22

Great work! Fantastic !!
Patta... patta.. elakiri.. elakiri.. Thani ahata adenawa oi...

sonicoliver on 2014-05-05 19:50:07

Nice work, thank-you!

Lucas on 2014-08-04 14:28:37

Nice. That's great.
Fantastic!!

visitor on 2015-02-10 13:53:19

perfect! really nice from You

Eduardo on 2015-06-29 18:09:43

Justo lo que necesitaba, Gracias!!!

on 2015-07-31 16:37:17

great

Sven on 2015-11-03 22:06:15

Works correct after I changed the function getDuration
from "return round($duration)" to "return $duration"
and call both functions with parameter false.

Before I did that about 3 of 10 files were wrong (1 second more or less)

You may check this issue.
Many thanks anyhow!