javascript - 对如何在node.js中实现异步回调感到困惑

Question

ytdl(url, { filter: function(format) { return format.container === 'mp4'; } })
    .pipe(fs.createWriteStream('./songs/Battle-Scars.mp4'));

我是node.js新手，正在尝试实现一个youtube-mp3转换器，但我不知道如何使以下代码仅在上面的代码完成运行后运行。

var proc = new ffmpeg({ source: './songs/Battle-Scars.mp4'})
    .withAudioCodec('libmp3lame')
    .toFormat('mp3')
    .saveToFile('./songs/Battle-Scars.mp3', function(stdout, stderr) {
        console.log('file has been converted succesfully');
    });

提前感谢所有的帮助和感谢。

Answer 1

由于您正在使用流，因此您可能需要查看 finish event一旦写入流完成写入磁盘，您就可以触发它。

尝试如下:

var writeStream = fs.createWriteStream('./songs/Battle-Scars.mp4');

// Set up event listener
writeStream.on('finish', function () {
  var proc = new ffmpeg({ source: './songs/Battle-Scars.mp4'})
    .withAudioCodec('libmp3lame')
    .toFormat('mp3')
    .saveToFile('./songs/Battle-Scars.mp3', function(stdout, stderr) {
      console.log('file has been converted succesfully');
    });
});

ytdl(url, { filter: function(format) { return format.container === 'mp4'; } })
.pipe(writeStream);