badger-am/lib/audio.js

// requirements
const fs = require('fs');
const path = require('path');
const async = require('async');
const metadata = require('musicmetadata');
const ffmpeg = require('fluent-ffmpeg');
const fse = require('fs-extra');
const util = require('./util');

// convert file to mp3 at specified bitrate
function convert(input, output, bitrate, callback) {
    output = path.join(path.dirname(output), path.basename(output, path.extname(output)) + '.mp3');
    async.series([
        function (asyncCallback) {
            fse.mkdirs(path.dirname(output), asyncCallback);
        },
        function (asyncCallback) {
            ffmpeg(path.normalize(input)).audioCodec('libmp3lame').audioBitrate(bitrate).save(output)
                .on('error', function (err) {
                    return asyncCallback(err);
                })
                .on('end', function () {
                    asyncCallback();
                });
        }
    ], function (err, results) {
        if (err) {
            return callback(err);
        }
        callback();
    });
}

// extract cover artwork
function extractArtwork(sourceFile, callback) {
    async.waterfall([
        function (asyncCallback) {
            extractMetadata(sourceFile, asyncCallback);
        },
        function (metadata, asyncCallback) {
            metadata.picture.forEach(function (picture) {
                const pic = path.join(path.dirname(sourceFile), path.basename(sourceFile, path.extname(sourceFile)) + '.' + picture.format);
                const stream = fs.createWriteStream(pic);
                stream.write(picture.data);
                stream.end();
                asyncCallback();
            });
        }
    ], function (err, result) {
        if (err) {
            return callback(err);
        }
        callback();
    });
}

// extract metadata for further processing
function extractMetadata(sourceFile, callback) {
    const stream = fs.createReadStream(sourceFile);
    metadata(stream, function (err, metadata) {
        if (err) {
            return callback(err);
        }
        stream.close();
        callback(null, metadata);
    });
}

// api
exports.convert = convert;
exports.extractArtwork = extractArtwork;
exports.extractMetadata = extractMetadata;