Reading duration of MP3 file from App script - google-apps-script

Question

I have a MP3 file in google drive. Is there a way I can get duraton of that MP3 file using google app script?

Answer 1

This page shows how to extract that information from an mp3 file by looking at the byte values.
So I wrote a short example and tested it. It seems to be working fine with all mp3 files I tried so far but there is no guarantee it will always work.
The getPlayTime function returns the play time in seconds.
function getPlayTime(file) {
var bitratesV1 = [0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320],
bitratesV2 = [0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160];
var bytes = file.getBlob().getBytes();
for(var pos = 0;pos < bytes.length; pos++) {
if(bytes[pos] === -1 && pos < bytes.length - 3 && (bytes[pos+1]&0xF0) === 0xF0) {
var isMpegVersion2 = (bytes[pos+1]&8) !== 8,
isLayer3 = (bytes[pos+1]&6) === 2,
bitRate = ((bytes[pos+2]&0xF0) >>> 4)&0xF;
if(!isLayer3) continue;
if(isMpegVersion2) bitRate = bitratesV2[bitRate];
else bitRate = bitratesV1[bitRate];
var playTime = bytes.length*8/(1000 * bitRate);
return playTime;
}
}
}
function test() {
var file = DriveApp.getFilesByName("music.mp3").next();
var playTime = getPlayTime(file);
Logger.log(playTime);
}
edit:
Here is a hopefully more accurate but also much slower version
function getRunTime(file) {
var playTime = 0, numFrames = 0;
var bitratesV1 = [0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320],
bitratesV2 = [0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160];
var bytes = file.getBlob().getBytes();
for(var pos = 0;pos < bytes.length; pos++) {
if(bytes[pos] === -1 && pos < bytes.length - 3 && (bytes[pos+1]&0xF0) === 0xF0) {
var isMpegVersion2 = (bytes[pos+1]&8) !== 8,
isLayer3 = (bytes[pos+1]&6) === 2,
bitRate = ((bytes[pos+2]&0xF0) >>> 4)&0xF;
if(!isLayer3) continue;
if(isMpegVersion2) bitRate = bitratesV2[bitRate];
else bitRate = bitratesV1[bitRate];
var pt = bytes.length*8/(1000 * bitRate);
if(!isNaN(pt) && isFinite(pt)) {
playTime += pt;
numFrames++;
}
}
}
return playTime/numFrames;
}