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);
    });
});

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);
    });
});