Node.js MP3 Header Parsing

npm install mp3-header

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``js
const fs = require("fs");
const Mp3Header = require("mp3-header").Mp3Header;

const HEADER_LENGTH = 4;

fs.open("filename.mp3", 'r', function(err, fd) {

var buffer = new Buffer(HEADER_LENGTH);

// The offset in the mp3 file where there is a valid MP3 frame
var offset = 0;

fs.read(fd, buffer, 0, HEADER_LENGTH, offset, function(err, bytesRead, buffer) {

if (err) {
return fs.close(fd);
}

var header = new Mp3Header(buffer);
if (header.parsed && header.is_valid) {
console.info("MP3 Sample Rate: ", header.mpeg_samplerate);
}

fs.close(fd);
});
});
`

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`js
const fs = require("fs");
const XingHeader = require("mp3-header").XingHeader;

const MAX_FRAME_LENGTH = 2881; // Theoretical max mp3 frame length

fs.open( "filename.mp3", 'r', function(err, fd) {

var buffer = new Buffer(MAX_FRAME_LENGTH);

// The offset in the mp3 file where there is a valid Xing header
var offset = 0;

fs.read(fd, buffer, 0, MAX_FRAME_LENGTH, offset, function(err, bytesRead, buffer) {

if (err) {
return fs.close(fd);
}

var header = new XingHeader(buffer);
if (header.parsed && header.is_valid) {
console.info("Number of audio frames: ", header.xing_frames);
}

fs.close(fd);
});
});
`

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The package exports two classes for parsing MP3 file headers: Mp3Header and XingHeader.

Mp3Header is the one that takes care of parsing the MPEG header of an MP3 audio frame, and provides informations about the encoding.

XingHeader is an extension Mp3Header that also takes care of parsing the metadata related to the Xing table of the MP3 file.

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Once you parse a header, these are the properties you can access from the package classes:


| Parameter | Type | Present in | Example |
| -------------------------- | -------- | ------------ | --------- |
| parsed | Boolean | Both | true |
| is_valid | Boolean | Both | true |
| mpeg_version | Integer | Both | 2 |
| mpeg_layer | Integer | Both | 3 |
| mpeg_has_padding | Boolean | Both | true |
| mpeg_channels | Integer | Both | 1 (mono) or 2 (stereo) |
| mpeg_bitrate | Integer | Both | 128000 |
| mpeg_samplerate | Integer | Both | 44100 |
| mpeg_num_samples | Integer | Both | 1152 |
| mpeg_frame_length | Integer | Both | 384 |
| xing_offset | Integer | XingHeader | 21 |
| xing_frames | Integer | XingHeader | 223 |
| xing_bytes | Integer | XingHeader | 43008 |
| xing_keyword | String | XingHeader | Xing (VBR) or Info (CBR) |
| xing_flags | Integer | XingHeader | |
| xing_has_frames | Boolean | XingHeader | true |
| xing_has_bytes | Boolean | XingHeader | true |
| xing_frames_offset | Integer | XingHeader | |
| xing_bytes_offset | Integer | XingHeader | |

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grunt test`

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* https://www.codeproject.com/Articles/8295/MPEG-Audio-Frame-Header
* http://gabriel.mp3-tech.org/mp3infotag.html

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MIT